Global GNSS, a subsidiary of Polosoft Technologies, has launched a new mobile application named GNSS Surveyor, which is designed for the geospatial industry.
The application GNSS Surveyor provides location information and quality position data in real-time with sub-meter to centimeter accuracy. It needs to be connected to any external GNSS receiver via Bluetooth.
Features of the application include:
A one-touch configured command to communicate directly with the GNSS Bluetooth device.
Location information and quality of the position data in real-time with centimeter accuracy.
GPS data such as position, height, satellites and velocity.
Constellation information for GPS, GLONASS, Galileo, BeiDou, QZSS and SBAS satellites in the orbit.
Direct IP feature for RTK corrections data.
DMS to DD conversion or vice versa.
Real-time kinematic (RTK) correction data can be forwarded to a high-accuracy external device. The internal NTRIP client loads the RTCM data from the internet.
With GNSS Surveyor, location information is collected as latitude and longitude, altitude, speed or pace, bearing and UTC time.
GNSS precision includes global coverage, centimeter-level accuracy, fast time to first fix, multi-constellation and multi-band, and highest security, the company said.
Navigation uses include ground robotics navigation, lane-level navigation, heavy machine navigation, industrial navigation and tracking and commercial UAV.
Virtual Surveyor drone surveying and mapping software has added new functionality that enables users to process larger projects without buying more powerful computers or cloud services, according to the company. This addition is one of several included in Virtual Surveyor 6.2.
“Our objective with Version 6.2 is to make our users more productive while saving them money by eliminating the need to invest in new hardware or processing services,” said Tom Op ‘t Eyndt, CEO of Virtual Surveyor in Belgium. “We have addressed the fact that drones are capturing more data at higher resolution, resulting in enormous files sizes.”
According to the company, Virtual Surveyor 6.2 solves the problem of large files by offering enhanced clipping and mosaicking functionality. The new version allows users to merge multiple smaller processed pieces of orthophotos and digital surface models into a single project and create smooth edges between these pieces with the new clipping tool. The mosaic can then be exported to a new tiff file or serve as the basis for a full area virtual survey.
In addition, Virtual Surveyor 6.2 offers a 3D Fly Through capability that allows users to select spatial bookmarks and waypoints in their scene and create a movie that allows the viewer to fly through the terrain in three dimensions.
Virtual Surveyor 6.2 also features improved surface handling for volume calculations. This feature was developed primarily for users who measure volumetrics of material piles in drone survey data. This capability makes it easy to represent topographies as triangles, contour lines or outlines without creating three different objects, the company said.
Other enhanced features of Virtual Surveyor 6.2 include a renumbering tool that allows users to select a set of times, features or geometries in the data set and automatically number them sequentially from any chosen starting number; concave hull extraction that allows users to select a section line to create a surface for a curved roadway; and boundary selection that allows users to trace around an unwanted feature and delete that object and all the points within it.
“The advantage of Virtual Surveyor is that it combines the interpretation skill of a professional surveyor with computing power to create standard survey products,” said Op ‘t Eyndt. “Surveyors can now accomplish more in Version 6.2 without expensive upgrades to other aspects of their workflow.”
Sokkia introduced the latest addition to its GNSS integrated receiver line — the GRX3. According to the company, the GRX3 is designed to provide a smaller, lighter and fully integrated GNSS solution.
Photo: Sokkia
“The multi-constellation GRX3 receiver is built to offer a complete and versatile solution to provide best-in-class positioning performance for a wide variety of precision applications,” said Alok Srivastava, director of product management.
“Whether using the receiver for GNSS post-processed surveying, or RTK using wireless technologies including network RTK option with a cellular-equipped field computer, a SiteComm RTK rover, or paired with a Sokkia total station for fusion positioning, the GRX3 provides the most advanced and powerful GNSS technology available in a more compact and lightweight housing that can withstand the harshest of environmental conditions. Combine it with one of Sokkia’s data collectors and field software for maximum versatility and convenience, increasing fieldwork efficiency from start to finish.”
The receiver features Sokkia Tilt technology, which includes a 9-axis inertial measurement unit and ultra-compact eCompass designed to compensate for mis-leveled field measurements by as much as 15 degrees.
“The GRX3 is designed as a ‘future-proof’ solution with an advanced GNSS chipset with Universal Tracking Channels technology that automatically tracks signals from all available and planned constellations — including GPS, GLONASS, Galileo, Beidou, IRNSS, QZSS, SBAS,” Srivastava said.
The receiver has been tested to meet IP67 certification for protection against harsh environmental weather conditions.
Topcon Positioning Group released a new workflow bundle designed to modernize concrete FFL (floor flatness and levelness) applications.
A new ClearEdge3D development and sales partnership with a leader and pioneer in 3D laser scanning software for construction QA/QC, Rithm, is prominently advancing the Topcon concrete application offering with a new hardware and software bundle option.
It is part of the Topcon comprehensive approach to modernize core concrete applications such as layout, quality control and concrete screed with the latest capabilities in precise positioning technology.
Implementing Rithm on projects for wet, or dry concrete scanning is designed to allow the opportunity to perform FFL analysis directly from scan data loaded into the Autodesk Navisworks software. Operators can find floor flatness and levelness mistakes in near real time from scan-to-finish. The data Rithm provides allows project teams to easily visualize high and low areas with elevation and deviation heat-maps and contour maps.
“By bundling this software with Topcon’s GLS-2000 scanner, contractors can improve their QA workflows to reduce floor profiling costs by performing FFL analysis in-house in near real time,” said Alok Srivastava, Topcon director of product management. “Through the integration with Navisworks, Rithm provides contractors fast, and detailed ASTM E1155 compliant FFL reports with streamlined floor flatness and levelness analysis, thereby cutting down time on waiting for scanning analysis, increasing productivity.
“The integrated workflow including the GLS-2000, post-processing with MAGNET Collage and QA analysis with Rithm software achieves an optimized end-to-end workflow — from the hardware to software end deliverables,” said Srivastava.
The new real-time FFL application is part of an overarching Topcon approach to modernize concrete applications with precise positioning technology.
Topcon GT series robotic total stations combined with integrated MAGNET software incorporate a BIM-integrated workflow to layout and verify construction quality in the field.
Additionally, Topcon offers machine control systems for robotic concrete screed applications. After importing an easily created 3D model, concrete can be poured and placed more efficiently with advanced screed technology designed to dramatically speed up the screed process and increase quality with precision-guided machine control.
“With our real-time position information constantly updating, you efficiently manage material as it’s placed — delivering the highest quality in a fraction of the time,” Srivastava said.
Orthometric height support (survey-grade elevations) enables Arrow GNSS receivers to collect high-accuracy, survey-grade vertical data with any data-collection software.
Eos Positioning Systems Inc. has added support for GEOID height models within its Arrow Series GNSS receivers. Eos manufactures high-accuracy GNSS receivers for any app running on iOS/Android/Windows devices and using the Eos Arrow Series.
“You can use Arrow Series receivers with any data-collection software in the world, and benefit from accurate orthometric heights,” Eos CTO Jean-Yves Lauture said. “Our Arrow receivers will output accurate GNSS elevations no matter which data-collection software you use to capture it.”
Image: Eos Positioning
With support for GEOID models, Arrow receivers automatically output survey-grade elevations to all iOS and Android data collection software. Support will also soon be available for Windows devices.
The Arrow receivers now support the entire United States to provide survey-grade elevation in NAVD88 orthometric heights through the GEOID12B (US) model. The Arrow receivers also support the Canadian CGG2013a and HTv2.0 GEOID models for the CGVD2013 and CGVD28 vertical datums, respectively. Additional GEOID models for other countries are planned.
“Eos is intensely focused on supporting high-accuracy GIS, engineering, surveying and construction users by supporting the latest GEOID elevation models within our GNSS monitoring software,” Lauture said. “Our roadmap remains focused on high-accuracy BYOD users by supporting all iOS, Android and Windows users with this capability.”
The problem is that typical Bluetooth GNSS receivers usually provide inaccurate, built-in elevation models. This inaccuracy is reflected in the Mean Sea Level elevation output by those receivers. By outputting orthometric height, the Arrow now solves this problem and turns any smartphone or tablet into a 3D, survey-grade accurate data collection device, the company said.
Eos has designed this new feature so that users will easily be able to update to new GEOID models as they become available.
Field technicians in pipeline, construction, engineering, architecture, water and any other industry are finally able to enjoy GNSS location with survey-grade vertical accuracy on their iOS and Android devices, with the data-collection app of their choice and their Eos Arrow receivers.
Tersus GNSS Inc. has released the Tersus GeoCaster, a Networked Transport of RTCM via Internet Protocol (NTRIP) caster software. The software expands the company’s product line and provides users with better and more comprehensive services.
The Tersus NTRIP caster software is designed to allow GNSS correction data such as RTCM corrections to be repeated and sent to different end users via the internet.
Screenshot: Tersus GNSS
“GeoCaster has a user-friendly interface, and it not only supports multiple bases online simultaneously but also supports multiple rovers for one base,” said Xiaohua Wen, founder and CEO of Tersus GNSS Inc. “Our users can have a real-time review of detailed statistics and can modify user-defined permissions manually.”
Tersus GeoCaster supports configurable bases online simultaneously and configurable rovers for one base. GeoCaster supports NTRIP protocol and operates continuously.
The software is designed for end users involved in applications such as surveying, construction engineering, deformation monitoring, automated vehicle, precision agriculture, unmanned aerial vehicle, machine control and robotics.
This is the first release of GeoCaster. Version 2.0, targeted at the first quarter of 2019, is expected to offer higher accuracy and longer baseline applications.
Mountainous areas present special problems for surveyors, overcome by the expanded availability of multi-GNSS. (Photo: Trimble)
Today’s GNSS satellites transmit on three or more carrier frequencies. The quality of the data in these signals from GPS, BeiDou, Galileo, GLONASS and QZSS reveals the expected measurement precisions. This article explores the noise of the range residual and ionospheric residual to indicate the oncoming capabilities.
Today, four GNSSs transmit various codes on various carrier frequencies: the USA’s GPS, Russia’s GLONASS, Europe’s Galileo and China’s BeiDou. Most of the carrier phase and pseudorange data are available using civilian GNSS receivers. Improvements in signal quality as well as reliability of the satellites are foreseen through the generations, as well as the introduction of new signals, such as L1C, L2C, L5 carrier and codes, and M-codes, on top of the existing L1-C/A code and the P(Y) code on both L1 and L2. Improvements are also seen in boosting the transmitting power.
This article investigates the use of two approaches to analyze the relative noise in the various carrier phase and pseudorange observable for GPS, BeiDou, Galileo, GLONASS and Japan’s Quasi-Zenith Satellite System (QZSS) augmentation. Two approaches analyze the relative noise in the observables: the range residual and the ionospheric residual. Both techniques can also be used to detect cycle slips.
Range Residual
UAV survey operations benefit from multi-GNSS receivers. (Photo: Septentrio)
The range residual is simply the change from one epoch to the next in the difference in the range calculated using the pseudorange and the range calculated by the carrier phase on a specific frequency. The pseudorange values are scaled using the wavelength to an equivalent range in units of the carrier’s cycles rather than meters. Equation 1 illustrates the range residual between the pseudorange ρ on a specific carrier frequency and the carrier phase observable φ, using the wavelength λ of the carrier to scale the pseudorange. The values of these observables are compared between adjacent epochs.
RR = (p/λ) – φ (1)
Two adjacent epochs are used, as then the integer ambiguity value, as well as the ionospheric and tropospheric errors, and satellite and receiver clock errors are the same, or negligibly different at such small (<1 s) epoch intervals. Therefore, these are all canceled out, and the resulting value is the measurement receiver and observable noise. The pseudorange observable will be significantly noisier than the carrier phase observable, therefore this method is a good way to calculate the measurement noise for the pseudoranges.
Ionospheric Residual
Surveyors work the Berezitovy mine in the North Amur region of Russia. (Photo: Javad GNSS)
If the carrier waves traveled only through a vacuum, then a phase observation from a specific satellite to a specific GNSS receiver could be scaled and converted to an equivalent phase measurement on another frequency using the frequencies of the carrier waves. However, as the signal passes through the ionosphere, systematic errors that are frequency dependent are introduced, so it is not possible to directly convert from one carrier phase value to another for a specific range measurement. The error is known as the ionospheric residual, and this will change slowly over time as the satellite passes overhead and the ionosphere being passed through changes, and also as the ionosphere slowly changes its characteristics over time, mainly due to the sun’s activities.
Equation 2 shows the calculation, using L1 and L2 carrier phase readings and corresponding frequencies, used to calculate the ionospheric residual. Again, the difference in the ionospheric residual values between adjacent epochs is used, as in the same way as the range residual values, external noise sources are eliminated.
(2)
Results
The results presented here are a subset of a much larger set. Figure 1 illustrates the range residuals for L1 and L2 as well as the L1L2 ionospheric residual for PRN32 (Block IIA satellite).
Figure 1. L1 range residual (left) L2 range residual (center) and L1L2 ionospheric residual (right) for GPS PRN32 (Block IIA) satellite. (Charts: Authors)
Figure 2 illustrates the L1 and L5 range residuals and the L2 (C-code) L5 ionospheric residual for PRN01 (Block IIF satellite).Both figures’ data are for the complete passing of the satellites from horizon over and back down again.The data for PRN32 is all that exists in the datafile, as this satellite only transmits L1 CA code and P(Y) code, as well as L2 P(Y) code, and corresponding carrier values.
Figure 2. L1 range residual (left) L5 range residual (center) and L2 (C code) L5 ionospheric residual (right) for GPS PRN01 (Block IIF) satellite. (Charts: Authors)
PRN01 is a block IIF satellite, and data for L1 CA code, L2 P(Y) code as well as L2 C-code, L5 code, and corresponding carrier phase values are recorded in the datafile.The block IIF satellites can result in four range residual values and five ionospheric residual combinations.Figure 2 only illustrates three of these combinations.The data were obtained from the Curtin University GNSS repository on Sept. 1, 2015, gathered at a 1-Hz epoch interval; 29,908 epoch of data were gathered for PRN32, and 26,073 epochs for PRN01.
It can be seen from these figures that the L1 range residuals are similar in characteristics for both PRN01 and PRN32.The values are noisy at the start and the end of the time series, indicating that the CA code is more prone to noise at low elevations.Comparing these to the L2 (PRN32) and L5 (PRN01) range residuals, we can see that both the L2 and L5 range residuals are not as prone to low elevation noise. Also, the two L2 and L5 range residuals are visually similar in characteristcs.By comparing the L1L2 and L2L5 ionospheric residuals (Figure 1, right, and Figure 2, right), we can see that the L1L2 combination is slightly noisier than the L2L5, in particular at low elevation angles.
If we compare BeiDou ionospheric residual results, we can see the comparison of noise on the three ionospheric residual combinations, B1B2, B1B3 and B2B3, as well as the results from the three types of satellite orbits, ie MEO, IGSO and GEO. Figure 3 illustrates the ionospheric residual results for PRN07 (IGSO) for the three frequency combinations, from data gathered on a static pillar located on top of the University of Nottingham Ningbo China’s Science and Engineering Building.
Figure 3. Ionospheric residual results for BeiDou PRN07 (IGSO) for combinations B1B2 (left), B1B3 (center), B2B3 (right). (Chart: Authors)
Figure 4 illustrates the ionospheric residual results for PRN01 (GEO) for the three frequency combinations.
Figure 4. Ionospheric residual results for BeiDou PRN01 (GEO) for combinations B1B2 (left), B1B3 (center), B2B3 (right). (Chart: Authors)
Figure 5 illustrates the ionospheric residual results for PRN12 (MEO) for the three frequency combinations. Here it can be seen that the B2B3 combination is generally less noisy than the B1B2 and B1B3. In addition to this, it can be seen that when the MEO and IGSO satellites are at lower elevation angles, the observables also become noisier. The GEO satellites have a constant elevation angle, and do not experience this phenomenon.
Figure 5. Ionospheric residual results for BeiDou PRN12 (MEO) for combinations B1B2 (left), B1B3 (center), B2B3 (right). (Charts: Authors)
Detailed Results
The data, gathered on a single GNSS receiver located at the University of Curtin’s GNSS research center, was downloaded in BINEX format and converted into RINEX 3.02 format using RTKLIB software. Software was developed by the authors in Matlab in order to interrogate the data files and implement the range residual and ionospheric residual algorithms. RINEX 3.02 format was chosen due to its compatibility with multi-GNSS and multi-frequencies.
Industrial UAV applications such as construction draw benefits from multi-GNSS receivers’ capabilities. (Photo: Skycatch, Swift Navigation)
Results are presented for both ionospheric residual and range residual results for various GNSS. These results have been calculated with varying elevation mask angles, ranging from 0° to 55° at 5° intervals. The RMS values of the resulting ionospheric residuals and range residuals were calculated and plotted against the respective elevation mask angle for each satellite and frequency combinations. This illustrates the influence of the elevation mask angle used on the results.
Typically, tens of thousands of epochs of data were used for every plotted point in the following figures. Further to this, not only are the results for the various frequencies and frequency combinations for the various GNSS illustrated, but also the various satellite types, MEO, GEO and IGSO, and various satellite Blocks for GNSS. GPS Block IIA (PRN04 and PRN32), Block IIR (PRN14), Block IIR-M (PRN31) and Block IIF (PRN01, PRN26, PRN25) data were all analyzed. Thus, the comparison of the various frequencies within each satellite system are illustrated, as well as the variations by comparing the various satellite constellation types and the various generations of GPS satellites.
Surveying accuracy is critical to roadway construction. (Photo: Leica Geosystems)
The BeiDou data illustrated are MEO (C12, C14, C11), IGSO (C09, C10, C07) and GEO (C01, C02). The data used were gathered on Sept. 1, 2015, in order to include GPS Block IIA satellites (PRN04 and PRN32). PRN32 was retired in June 2016, and PRN04 was taken out of active service in November 2015, but the satellite was reactivated in March 2018, this time broadcasting PRN18.
Figure 6 illustrates RMS of the range residual results for GPS (a), BeiDou (b), Galileo (c), GLONASS (d) and QZSS (e) respectively. These figures have been drawn so that the y-axis ranges are the same for each, hence illustrating the relative values.
Figure 6A illustrates the range residual results for GPS. It can be seen that the L1 CA code results are the noisiest, with PRN14 being the noisiest, followed by PRN31, PRN26, PRN01, PRN04, PRN25 and PRN32. It can also be seen with these results that lower elevation angle mask increases the noise level. Both the L2 and L5 code results are less noisy.
Figure 6A. RMS range residual results for GPS. (Chart: Authors)
Looking at the detail, the L5 code results is less noisy than the L2 and affected less than the L1 results by the changes in elevation mask angles used. Interestingly enough, the data file includes both the L2 P(Y) code and L2C code results. L2C only exists on the Block IIR-M and Block IIF satellites. The L2C code results are generally noisier than the L2 P(Y) code.
Figure 6B illustrates the results for the range residuals for the BeiDou satellites. Here it can be seen that the B1 code is affected more by low elevation mask angles than B2 and B3. It can also be seen that both the geostationary satellites’ B1 results stand out, with satellite C02 being noisier than C01. The B2 and B3 values for both these GEO satellites are bunched up with the majority of the other results towards the middle of the figure. The pairs of B2 and B3 results for the GEO satellites are close to each other in values, and the pairs of B2 and B3 results for the other satellites are also close to each other.
Figure 6B. RMS range residual results for BeiDou. (Chart: Authors)
It can also be seen that the range residual results for BeiDou are generally less noisy than than GPS, in units of cycles.
Similarly, for Galileo, Figure 6C, the E1 results are worst, and affected more by low elevation masks. Again, generally the Galileo results are seen to be improved over GPS. The GLONASS results, Figure 6D, illustrate that the L1C results are generally noisier, and then the L1P, followed by L2C and L2P. PRN09 is also consistently generally noisier than PRN10. Finally, Figure 6E illustrates the results for QZSS. Again, L1C is the noisiest and affected most by low elevation mask angles.
Figure 6C. RMS range residual results for Galileo. (Chart: Authors)Figure 6D. RMS range residual results for GLONASS. (Chart: Authors)Figure 6E. RMS range residual results for QZSS. (Chart: Authors)
Figure 7 illustrates the ionspheric residual results for the same satellites as Figure 6. This time, however, the resulting ionospheric residual values are calculated using pairs of data from the same satellite on different carrier frequencies. The range residual results compare the code and carrier from specific satellites and frequencies.
Figure 7(a) shows that the ionospheric residual results are affected by low elevation masks, and that the L1L2CW (L1 CA code and L2 P(Y) code available on all the satellites) combinations are the noisiest, followed by L2L5WX (L2 P(Y) code and L5 code available on Block IIF satellites, PRN 26, PRN01, PRN25), followed by L1L2CX (L1 CA code and L2 C code available on Block IIF and Block IIR-M satellites, PRN31, PRN26, PRN01 and PRN25), followed by L1L5CX (L1 CA code and L5 code, Block IIF satellites, PRN01, PRN25, PRN26) and finally the least noisy were the L2L5XX results (L2 C code and L5 code available on Block IIF satellites, PRN26, PRN25 and PRN01).
Figure 7A. Ionospheric residual results for GPS. (Chart: Authors)
Figure 7(b) illustrates the BeiDou ionospheric residual plots, illustrating that satellite C14 is much noisier for all three combinations of B1B3, BB1B2 and B2B3 in that order. The B1B2 combinations for the satellites are generally the noisiest, and then the B1B3 and B2B3 combinations are intertwined. The Galileo results again illustrate that the E1 combinations are generally noisier, and again we see the effect of low elevation angle masks, Figure 7(c). Generally, however, the Galileo results are less noisy than GPS, as are the BeiDou results.
Figure 7B. Ionospheric residual results for BeiDou. (Chart: Authors)Figure 7C. Ionospheric residual results for Galileo. (Chart: Authors)
The GLONASS results are again generally the noisiest, and again PRN09 is noisier than PRN10, with the L1P combinations being noisier, Figure 7(d). Figure 7(e) for QZSS shows that there are generally two groups of results. The upper set consists of L1L2ZX, L1L5ZX, L1L2XX, L1L5XX, L1L6ZX and L1L6XX from highest to lowest noise respectively. The lower, less noisy, group consists of L1L2CX, L1L5CX, L2L5XX, L2L6XX, L1L6CX and L5L6XX from highest to lowest noise respectively. Further details about the various codes and carrier values can be found in the RINEX 3.02 manual produced by the IGS.
Figure 7D. Ionospheric residual results for GLONASS. (Chart: Authors)Figure 7E. Ionospheric residual results for QZSS.(Chart: Authors)
Conclusions
A surveyor checks an urban construction project. (Photo: Topcon)
These preliminary results illustrate that there are differences in the noise values for various GNSS, frequencies as well as satellite generations and orbit types. It can be seen that generally L1, B1 and E1 have noisier results, and are affected moreso by low elevation mask data, and hence multipath. It can also be seen that newer generations of satellites do indeed produce better quality data.
Some specific satellites produce lower quality data such as GLONASS PRN09 and BeiDou C14. This could be due to multipath produced at the satellite.
Today roughly 100 GNSS transmit data, and typically users can gather data from 30 to 50 at any time. Positioning requires nowhere near this number of satellites, therefore decisions are needed as to which satellites and which data to use in a positioning solution. Our findings imply that our approach could be used in such decision-making in GNSS processing software, helping the software to choose the optimum satellites to draw from in a positioning solution.
Acknowledgments
This work described in this article was first presented at the FIG 2018 conference held in Istanbul, Turkey. The authors acknowledge the use of data supplied from the Curtin University GNSS Centre.
Manufacturers
The GNSS receiver used is a Trimble NET R9, and the antenna is a Trimble TRM 59800.00 SCIS choke ring antenna. A ComNav K508 GNSS receiver supplied some of the BeiDou results.
GETHIN WYN ROBERTS is an associate professor at Fróðskaparsetur, the University of the Faroe Islands. He is past Chairman of the FIG’s Commission 6, Engineering Surveys, and previously held posts at the University of Nottingham both in the UK and in China. He holds a Ph.D. in engineering surveying and geodesy from the University of Nottingham.
CRAIG M. HANCOCK is an associate professor in Geodesy and Surveying Engineering and the head of the Department of Civil Engineering at the University of Nottingham, Ningbo, China as well as the head of the Geospatial and Geohazards Research Group. He holds a PhD from the University of Newcastle Upon Tyne.
XU TANG is a research fellow at the University of Nottingham, Ningbo, China. He holds a PhD from Nanjing University.
Calendar pages allows seem to fly by quickly, and 2018 was no different. While many of the items discussed in last year’s review continued to be topics of advancement, there are several new sources of technology, data collection and potential issues for surveyors going into the new year.
Let’s look back at the stories that affected the surveyor and their use of GNSS technology in 2018.
FCC broadband accuracy
The race across America to provide better broadband coverage hit a snag late in 2018 when critics of the Federal Communications Commission (FCC) voiced their displeasure with the accuracy of maps produced to depict the coverage of broadband access.
These critics are pressuring the FCC to verify internet coverage and speed of data availability in rural areas as reported by the broadband companies.
The FCC unveiled a new broadband map in February 2018. (Image: FCC)
These broadband companies are only required to report on the advertised availability and data speeds and not the actual coverage/speed of the installed networks. Critics of the FCC have found that information used from the broadband providers overstates the available speeds and number of internet service providers, thus allowing the FCC to produce mapping of broadband that is not correct.
Because of this incorrect reporting, it is estimated that almost 40 percent of rural America doesn’t have access to broadband data with no formal plan of rectifying this situation. The FCC has stated that they will investigate these coverage maps in order to determine if monies distributed to broadband providers were not used in accordance with the promised delivery of coverage and data speed.
Why does this matter to surveyors? As previously discussed in past columns, the reliance on the real-time network capability of GNSS is one of the biggest time and production savers for the surveyor and for those working in rural America is no exception.
Not just in small towns but out in the open where large parcels are being surveyed for many different reasons, including pipelines, wind and solar installations and title conveyances. By having broadband available use by surveyors, these tasks can be accomplished with shorter timeframes and less steps to keep critical data in compliance with established coordinate systems.
While this bill received lots of attention because of the FAA implications, the portion of the bill concentrating on geospatial oversight will have a lasting effect on the governance and development of the national mapping industry.
For many years, the ever-developing amount and sources of geospatial data has been growing within several different agencies of the United States government. This bill was established to help streamline the efforts and availability of geospatial data by assigning specific agencies to oversee the development and introduction of new technologies.
The biggest takeaway from this bill will be the reduction of agencies working on concurrent data sets for public and private use and therefore streamlining the opportunities to introduce newly acquired information into critical programs, (such as FEMA floodplain mapping, GAO asset management, etc.).
Part of the reason I wish to highlight this bill was the efforts of the National Society of Professional Surveyors (NSPS) to keep the state professional licensing laws intact, the use of private sector businesses for providing surveying services, and to keep quality-based selection (QBS) as the primary tool for awarding contracts for procurement services.
Because of the actions and reasoning by NSPS, the authors of the bill withdrew the language that would allow “low bid” opportunities within these contract awards. This influence by NSPS is a prime example of how a profession can influence legislation through our democratic process.
Galileo implementation, Beidou installation, GPS Block III launches
SpaceX’s Falcon 9 rocket orbited the first GPS III satellite on Dec. 23, 2018. (Photo: SpaceX)
In November 2018, the FCC opened a new chapter in GNSS observation by approving a waiver to allow GNSS receivers to utilize Galileo transmissions for location determination without a specific FCC license. Traditionally, the FCC would require licensing of public, receive-only GNSS equipment used with any foreign-based systems but worked with several US agencies to create a waiver to allow faster implementation to use the Galileo signals.
It should also be noted that the Chinese government has been rapidly building the latest stage of their own GNSS constellation, the BeiDou system. The United States and China have been promoting cooperation to allow each side to better understand the current workings of GPS and BeiDou, (GPS-BeiDou Statement). China is currently completing its third phase of the navigation system that potentially will surpass the United States GPS constellation in data availability and accuracy, (See GPS World“Directions 2019: BeiDou accelerates global deployment,” December 2018).
Not to be outdone, the U.S. has begun its implementation of their next wave of satellites, the GPS III containing the latest technology, the L1C civil signal, with improved accuracy and anti-jamming programming. On Dec. 23, the SpaceX Falcon 9 rocket delivered the GPS III SV01 into its intended orbit (SpaceX Launch) with more launches scheduled for additional satellite vehicles in 2019.
These efforts to increase satellite coverage and accuracy will only improve the use of GNSS receivers by surveyors. While I look forward to software and receiver upgrades to take advantage of the newer birds, we still need a backup plan in case of international conflicts and a reduction/discontinuation of GNSS service.
GPS and terrestrial backup
The Frank LoBiondo U.S. Coast Guard Authorization Act of 2018, which also included the National Timing Security and Resilience Act, was signed into law on Dec. 4 and directs the Secretary of Transportation to establish a terrestrial back system for the U.S. satellite navigation system within a two-year period (see “GPS to get terrestrial backup system”).
The bill lays out specific conditions for the backup plan:
terrestrial
wireless
synchronized to UTC
difficult to disrupt
able to penetrate underground and inside buildings
capable of deployment to remote locations
expandable to provide position, navigation and timing (PNT), and
able to work in concert with similar systems such as eLoran.
However, this bill did not provide any funding for the creation of this system but now allows the introduction of appropriations in future bills and acts. As I have written in past columns (see “The day GPS went away,” September 2017), it won’t be a matter of if but when something happens to our current GNSS capabilities and we need to develop this backup plan yesterday.
Dual-band GNSS cellphones as the new norm
My last submission featured the latest in chipset for cellphones and utilizing dual-frequency GNSS signal reception. Xiaomi, based in Beijing, China, introduced the Mi 8 phone with a dual-frequency GNSS chip in the Spring of 2018 to rave reviews.
This chip frequency reception (E1/L1+E5/L5) is targeted to embrace the Galileo and GPS constellations for increased accuracies (within a decimeter) well beyond the current norm for smartphones (typically 1-3 meters +/-).
Since then, Xiaomi has released the Mi Mix 3 and Huawei has released the Mate 20, Mate 20 Pro and Mate 20 X, all with dual-frequency chipsets. However, all of these phones are not available in the U.S., and the security issues with Huawei has been well documented (CNBC Report, February 2018).
The reason I still bring these up for the surveyor is because soon we will have dual-frequency capability on the phone in our pockets here in the U.S. Such phones can greatly increase efficiencies, especially when used during reconnaissance efforts. I believe many more phone manufacturers will begin to incorporate dual-frequency chips in their future models to increase location accuracies for the users and take advantage of upcoming network enhancements (see GPS World“Dual-frequency GNSS smartphone hits the market,” June 2018.)
Surveyors vs. technology disruptors
The Mi 8 smartphone offers dual-frequency capability. (Image: Xiaomi)
One of the biggest stories in the surveying world made national headlines after a start-up “GEO-spatial” consultant created by retired bankers was sued by the Mississippi Board of Licensure for Professional Engineer and Surveyors for having “engaged, and continues to engage in the practice of surveying while not licensed by the Board.” (Madison County, Mississippi, Chancery Court.) While the initial suit remained under the national radar, the countersuit by the consultant and subsequent articles in national websites brought the situation to the front page.
The issue at hand is the creation of “plats” combining a legal description for a parcel with a high-resolution photo (captured by various means, including UAV) and depicting said legal description on the photo for use by banks and other financial institutions for risk evaluation. Their argument is that they have “First Amendment rights” to provide public information (the legal description) on a recent aerial photograph in order to provide an exhibit for lenders to review and make loan decisions. Banks are now paying much less in fees to this company for an exhibit instead of a Plat of Survey provided by a licensed surveyor, yet the exhibit provides no assurance (or certification) to its validity and/or any metadata for the represented information.
The subsequent articles by both Bloomberg and Ars Technica writers liken the situation to Airbnb versus hotels and Uber/Lyft versus taxi drivers as a new “disruption in technology” brings forth change to previously licensed professions. In fact, the author of the Bloomberg article stated, “the clients are sophisticated, and they’re not complaining.”
Using this mentality, we could apply it to any licensed profession and allow services normally regulated by laws to be administered by non-professionals, as long as the client “is sophisticated and not complaining.” This means anyone can provide accounting, medical, dental or even law services if the client is satisfied. As previously published here, (see GPS World“Accuracy, precision and boundary retracement in surveying” July 2017), a boundary survey is not simply a mathematical figure from a legal description. It takes a trained person to know how to properly relate a legal description to a physical parcel and professional licensing provides that assurance (and protection) to the public.
This situation falls squarely in the GNSS wheelhouse for surveyors, especially as technology advances and accuracies become smaller with progress, (i.e. GPS Block III, BeiDuo, Galileo, etc.) and the ability to measure with higher positional accuracy, (i.e. Xiaomi Mi 8 and other to follow).
The surveying profession has joked for years that when these technologies do come forward, many unlicensed “professionals” will come forward with their measuring devices (phones) and locate property lines as part of their service.
But for now, it isn’t just the physical location by GNSS measurement we should worry about; it is the high-resolution photo software, GIS data sources and those folks enterprising enough to put all this information together. The surveying profession will need to ramp up its message to public to help better define what the licensed surveyor provides versus the “we can do it much cheaper and faster” stories. More often than not, you get what you pay for.
Data collection advancements
Emlid Reach RS with iPad. (Photo: Tim Burch)
While 2018 didn’t see any revolutionary changes to GNSS data collection, several small advances are noteworthy. Besides the previously mentioned dual-frequency cellphones, we are also seeing more integration with the cellphones themselves as data collectors in conjunction with stand-alone GNSS receivers (see GPS World“University research uses smartphones for precision GNSS,” September 2018).
Several of the major survey equipment manufacturers are joining a group of small GNSS start-ups by introducing single- and dual-frequency receivers to work with both Android- and iOS-based phones and tablets for more cost-effective positional solutions.
Another trend that is becoming very popular is the use of post-processing kinematic (PPK) solutions with many of the newest models of multi-rotor and fixed wing UAVs. The early (and expensive) trend of aerial vehicles produced by the major surveying equipment manufacturers insisted on installation of a dual-frequency RTK receiver in order to provide a more robust control system for the orthometric photo process. Because there is still a need to combine the still photos from the UAV flight via various “stitching” software, the need (and expense) of RTK within the receiver, while a nice feature, has become overkill for most aerial needs. However, there are times and applications when a fixed-RTK location could be useful, especially during emergency situations when needing to utilize the UAV for live streaming purposes.
The last big trend to gain popularity comes from Propeller, a young tech company from Australia that provides both a control point product and data reduction/reporting service. Their revolutionary ground control point (GCP) target, the Aeropoint, is becoming a very popular item for UAV pilots worldwide. These 24-inch (61-CM) square foam targets contain a single-frequency GNSS receiver that collects RINEX data while performing your UAV flight. Spread these targets around your site, setup and perform your survey, then download the target data to the Propeller app on your phone/tablet. The app automatically uploads the data to the company’s site and processes the geographical location for each target into your chosen coordinate system. It truly is that simple and the Propeller folks have made it easy to use. Their online software, Propeller Platform, is also available for photo/data processing and site analysis/visualization/volume computations. They, too, are now teaming with DJI to offer PPK solutions combining Aeropoint data along with Phantom 4 RTK photo data in a convenient, streamlined process.
For 2018, our firm (SPACECO Inc) expanded our UAV program in several ways to take advantage of these trends. First, we been using the Emlid Reach RS single-frequency GNSS receiver utilizing a Bluetooth connection to an iOS-based tablet to GCP’s for our UAV program. The receiver’s low cost and ease of use with an RTN network has been a pleasant change from typical surveying equipment. We also use Propeller’s Aeropoints in locations where the RTN coverage is not readily available. For sites that are substantial (typically 300 acres+), we often send our data to the Propeller Platform for photo stitching and data reduction to take advantage of their computing power.
WingtraOne. (Photo: Brian Kravets, SPACECO Inc.)
Lastly, we wanted to expand our fleet of quad-rotor UAV’s to include a fixed wing model for larger sites. A visit with the Wingtra crew at InterGeo 2017 in Berlin convinced me that a vertical take-off and land (VTOL) model would be a great addition, so we took delivery of our WingtraOne this past summer. The ease of use and amount of project space the Wingtra can cover was already great but we’ve added the PPK module to reduce the amount of GCP’s necessary, especially in inaccessible areas. All these additions to our survey department (carefully vetted and purchased; no freebies from any of the manufacturers!) have provided new ways to expand our services to our clients and allows us the opportunity to enjoy what we do along the way. It is my pleasure to report from personal experience that these trends are solid and will continue to increase our abilities and productivity for days to come.
What’s next for 2019?
Some of the items I see gaining traction in 2019 will include additional sensors for UAV’s (LiDAR, hyperspectral, infrared), continued improvement in cost effectiveness of laser scanners and LiDAR, increased interest in SLAM (simultaneous localization and mapping) technology and, of course, more geolocation services tied into autonomous vehicles/delivery. Will 2019 be the year Amazon drops my packages by UAV at my front door? As fast as these technologies are developing, I wouldn’t bet against it.
The Faro Focus scanner attached to a Stormbee UAV. (Photo: Stormbee)
3D measurement and imaging company Faro has joined with UAV provider Stormbee to offer an integrated airborne 3D scanning solution designed to quickly gather large area data for crash scene documentation, security pre-planning and military applications.
The integrated solution includes the Faro Focus laser scanner, the Stormbee S series UAV and the Beeflex software suite.
The airborne solution enables wide-area scanning missions, such as highways, train infrastructure, and buildings. While these would take days when scanned from the ground, they can now be completed in just hours without interrupting traffic or setting foot in a zone of interest.
The Faro Focus laser scanner. (Photo: Faro)
The solution further enhances productivity by allowing users to capture complex environments where traditionally would be inaccessible to ground based scanning and levels of accuracy and detail from the air with exceptional.
The data can then download to FARO Zone for crash reconstruction, security pre-planning, military reconnaissance.
The Faro–Stormbee airborne solution has no need for control points, meaning is quicker to start scanning an area compared to other lidar drones. Drone pilots can fly with ease as it goes up to 100 meters (328 feet) in the air. With the drone’s integrated redundancy, even if a propeller or battery fails the UAV still flies.
“Stormbee has developed and validated its UAV credibility from real-life testing in the most rigorous environments,” said Liesbeth Buyck, CEO of Stormbee. “As a result, we are confident that this turnkey solution, that includes the Stormbee UAV and the FARO Focus laser scanner, creates a new reliability and quality benchmark for airborne 3D data capture solutions.”
Users can create centimeter-level accurate point clouds directly from the in-flight data. The user-friendly Beeflex software takes little training to use and can be exported directly into Faro Scene or Faro Zone 3D software for further analysis or to combine aerial scans with the detail-rich data from terrestrial scanners.
The Faro scanner can detach from the drone and be used as a terrestrial scanner or even a mobile mapper. This flexibility allows users to use one scanner in the air, on land or affixed to a vehicle.
Combined with Faro’s Focus laser scanner compact design, IP54 rating and laser technology users can scan a vast variety of scenarios, from large areas (railways, cities), areas with no light (tunnels, burned buildings), and hard-to-document areas (cluttered crime scenes, inside dumpsters).
RINEX 3.04 contains updates to support planned GLONASS CDMA signals, as well as new BeiDou III and QZSS II signals.
The International GNSS Service (IGS) and Radio Technical Commission Maritime Service, Special Committee -104 (RTCM SC-104) RINEX Working Group, announced the availability of RINEX 3.04.
RINEX 3.04 supports all publicly available signals from existing GNSS constellations: the U.S. GPS, Russia’s GLONASS, Europe’s Galileo, China’s BeiDou, Japan’s Quasi Zenith Satellite System (QZSS) and the Indian Regional Navigation Satellite System (IRNSS).
In addition to the new signals, the RINEX 3.04 text has been edited to improve the description of messages, fields and overall readability.
The RINEX 3.04 data standard documentation is available here:
Added new signals to the GLONASS (Table 5), QZSS II (Table 8) and BeiDou III (Table 9) signal tables and updated Table A23
Added section 9.12 to describe new signals from the GLONASS, QZSS II and BeiDou III constellations and to describe the differences between QZSS I and QZSS II
Updated Appendix Table A2 SYS/#/OBS TYPES to show new signal codes for: GLONASS, QZSS II and BeiDou III
Modified Appendix Table A5 TIME SYSTEM CORR section to clarify the GNSS time system and UTC difference fields
Added numerous small corrections and text improvements as listed in the RINEX 3.04 Revision History section.
Allystar Technology Co. Ltd., headquartered in Shenzhen, China, has released a multi-band multi-GNSS chipset, the HD9310. The new product is based on the Cynosure III architecture integrating multi-band multi-system GNSS RF and baseband.
A multi-band, multi-system system-on-chip, it supports BeiDou-3 and is capable of tracking all global civil navigation systems (GPS, BeiDou, Galileo, GLONASS, IRNSS, QZSS and SBAS) in all bands (L1, L2, L5, L6), said Simon Sun, Allystar general manager.
Photo: Allystar Technology
Designed for high-precision applications, the HD9310 measures 5.0mm x 5.0mm. The architecture integrates floating-point arithmetic units based on ARM CortexM4, 160 KB RAM, 32KB backup RAM with VBAT, 386 KB embedded FLASH and peripheral interfaces UART, I2C, SPI, GPIO, CAN.
In terms of the manufacturing processes, it adopts a 40nm process and incorporates a variety of advanced design technologies, endowing it with very power consumption: less than 50mA.
The quad-flat no-leads package allows customers to reduce printed circuit board and bill of materials costs while reducing the number of peripheral devices. This chip supports CAN interface and can be widely used in vehicle management, car navigation, wearable devices, GIS data collection, precision agriculture, smart logistics, driverless, engineering survey and other fields.
“The HD9310 supports three options of RF setting — A, B, C — for product developers to quickly bring their ideas to the different application and markets,” added Shi Xian Yang, high precision project manager at Allystar.
Three available options for the HD9310 chipset. Graphic: Allystar Technology
Option A, focused on L5 band, L5/E5, maximizes measurement accuracy and improves multipath mitigation based on higher chip rate.
Option B is focused on L2 band, and suitable for relative position applications, for example, real-time kinematic (RTK), because worldwide continuously operating reference stations (CORS) commonly support L1/L2/L1OF/L2OF.
Option C is focused on the L6 band and is designed for PPP applications, receiving state space representation (SSR)-type corrections to be broadcast from satellites in the coming future, and supporting B3I already.
The HD9310 comes with built-in support for standard RTCM Protocol (MSM), supporting multi-band multi-system high-precision raw data output, including pseudo range, phase range, Doppler, SNR for any kind of 3rd party integration and application.
Module. Allystar Technology also has launched a multi-band multi-GNSS module, TAU1302, which integrates the HD9310 chipset and measures 12 × 16 × 2.3 millimeters.
With the features of small size, low power consumption (<50 mA), and ease of integration and mass production, HD9310 is suitable for high-precision applications such as vehicle management, car navigation, wearable devices, GIS data collection, precision agriculture, smart logistics, driverless, engineering survey and other fields.
Customer samples of the HD9310 chipset are available now.
On Aug. 10, the National Geodetic Survey (NGS) released its latest experimental geoid model, xGeoid18. In early 2019, NGS is scheduled to release its next hybrid geoid model, Geoid18.
NGS’ 2018 experimental geoid model, xGeoid18, and the next hybrid geoid model, Geoid18, are not the same. This column will address the latest experimental geoid model, xGeoid18, and the future hybrid geoid model, Geoid18, and why it’s important to understand that they are very different and cannot be interchanged.
In my October 2015 column, I described the differences between NGS’ hybrid geoid models and their experimental geoid models. It has been three years since I wrote the newsletter that addressed the differences between the experimental geoid model and hybrid geoid models. NAPGD2022 is now only about three years away. There will be significant differences between NAVD 88 and NAPGD2022 height.
My June 2017 column provided an estimate of the differences based on the 2016 experimental geoid model, xGeoid16b. These differences between NAVD 88 and NAPGD2022 will vary from state to state, as well as within an individual State. Products referenced to NAVD 88 will be different from products referenced to NAPGD2022. Users will need to prepare for the NAPGD2022 and develop implementation plans. Users should obtain an understanding of the differences between NAPGD2022 and NAVD 88.
Photo: National Geodetic Survey. Click to enlarge.
If the user clicks on the xGeoid18 button (see orange arrow in the box titled “NGS’ Experimental Geoid Web Site”), the experimental geoid model xGeoid18 web page appears (see box titled “NGS’ Experimental Geoid Models 2018 Web Site”).
Once users get to the xGeoid18 web site, they can obtain estimates of xGeoid18 values for any latitude and longitude by clicking on the button titled “Interactive Geoid Computation.” See red arrow in box titled “NGS’ Experimental Geoid Models 2018 Web Site.”
Input Page of xGeoid18 Interactive Web Page Using the Sample Dataset
Users should note that the output of the xGeoid18 interactive web service provides the results in IGS08 epoch 2022.00. The output provides an estimate of the NAVD 88 orthometric height based on GEOID12B, an estimate of the NAPGD2022 orthometric height based on xGeoid18b, and the difference between NAPGD2022 and NAVD 88. The box titled “Output from xGeoid18 Interactive Web Page Using the Sample Dataset” shows the output from the interactive web service using the sample dataset provided by the web service.
The sample dataset has four stations — a station in California, Louisiana, Michigan and Maine. The results indicate that the differences will vary from state to state — the difference between NAPGD2022 and NAVD 88 in California using xGeoid18b is -0.722 meters, in Louisiana the difference is -0.274 meters, in Michigan the difference is -0.646 meters, and in Maine the difference is -0.307 meters (see box titled “Output from xGeoid18 Interactive Website Using the Sample Dataset”). More detailed estimates of differences between NAPGD2022 and NAVD 88 based on xGeoid16b can be found in my June 2017 column.
Output from xGeoid18 Interactive Website Using the Sample Dataset
Note: The GRS80 ellipsoid is used for both NAD83 and IGS08.
Users can find technical information on xGeoid18 by clicking on the link labeled as Technical Details on the xGeoid18 website (see blue arrow in box titled “NGS’ Experimental Geoid Models 2018 Web Site”). The box titled “Excerpt from Technical Details for xGEOID18 Models” provides an excerpt of the technical details of xGeoid18.
Summary xGEOID18 is identical to xGEOID17 in the area bordered by 5˚ ≤ φ ≤ 85˚, 170˚ ≤ λ ≤ 350˚, which includes CONUS, Alaska, Hawaii, and Puerto Rico. Therefore, for information on xGEOID18 in those areas, the user should refer to the Technical Details of xGEOID17.
For extended areas down to the equator and above latitude 85˚ north, the geoid is computed from the NGA’s Preliminary Geopotential Model 2017 (PGM17).
The geoid models for Guam/central Northern Marianas Islands and American Samoa are computed in the closest way as xGEOID17 using the shipborne gravity, altimetric gravity and the reference gravity model PGM17.
The deflections of the vertical are computed from all the geoid grids and the plumb curvature correction is applied by using the classical Bouguer reduction.
As the technical detail webpage states, xGEOID18 is identical to xGEOID17 in the area bordered by 5˚ ≤ φ ≤ 85˚, 170˚ ≤ λ ≤ 350˚, which includes CONUS, Alaska, Hawaii and Puerto Rico. Therefore, for information on xGEOID18 in those areas, the user should refer to the Technical Details of xGEOID17. The box titled “Excerpt from Technical Details for xGEOID17 Models” provides an excerpt of the technical details of xGeoid17. This link provides figures that show the contribution of the airborne gravity data to the geoid models. See boxes titled “Excerpt from Technical Details for xGEOID17 Models” and “Figure (2,3,4,5) from Technical Details for xGEOID17 Models.” As stated in the technical details, users can examine each of the regional plots to see where the incorporation of GRAV-D data has changed the values of the xGeoid17B model.
The xGEOID17A and xGEOID17B models are identical except that xGEOID17B includes the available GRAV-D airborne gravity data. The difference between the two models shows the contribution of the airborne gravity data to the geoid models. Since the differences are only in areas where the GRAV-D airborne gravity data has been used, examining the regional plots given below will illustrate the varying levels of improvement due to GRAV-D, seen in different parts of the country.
Figure 1. CONUS – Contribution of GRAV-D airborne gravity [units in cm]
Figure 2 from Technical Details for xGEOID17 Models
Figure 2. Alaska – Contribution of GRAV-D airborne gravity [units in cm]
Figure 3 from Technical Details for xGEOID17 Models
Figure 3. Gulf Coast – Contribution of GRAV-D airborne gravity [units in cm]
Figure 4 from Technical Details for xGEOID17 Models
Figure 4. Northeast – Contribution of GRAV-D airborne gravity [units in cm]
Figure 5 from Technical Details for xGEOID17 Models
Figure 5. Pacific Coast – Contribution of GRAV-D airborne gravity [units in cm]
What does mean to a user today? A station can now have a published ellipsoid height, modeled GEOID12B value, a published NAVD 88 orthometric height, and several xGeoid modeled values. This can lead to confusion if the user is not careful about providing the correct metadata associated with their data and results.
The box titled “Excerpt from The NGS Data Sheet for Station E 116 (PID GA0589)” provides the output from NGS data sheet retrieval program. The first item to note is that if you compute the GNSS-derived orthometric height (HGNSS) using the formula:
Equation: National Geodetic Survey
the computed value does not equal the published NAVD 88 leveling-derived orthometric height. In this example, the two heights differ by 2.3 cm. As explained in a previous column, GEOID12B is a hybrid geoid model that is distorted to be consistent with NAVD 88 published heights. It is a model and the documentation states that “The relative accuracy of GEOID12B to NAVD88 is characterized by a misfit of +/-1.7 centimeters nationwide.” The box titled “Excerpt from The NGS Data Sheet for Station E 116 (PID GA0589)” provides the computations and the results.
Excerpt from The NGS Data Sheet for Station E 116 (PID GA0589)
Users can also obtain a xGeoid18B value for the station. The box titled “xGeoid18 Output for Station E 116 (PID GA0589)” provides the output of the xGeoid18 using NGS’ xGeoid18 interactive web service. It should be noted that the xGeoid18 output only provides the NAVD 88 orthometric height using GEOID12B; it does not include the published NAVD 88 orthometric height from the NGS Datasheet.
xGeoid18 Output for Station E 116 (PID GA0589)
Note: The GRS80 ellipsoid is used for both NAD83 and IGS08.
The box titled “Different Height Values for Station E 116 (PID GA0589)” provides three different height values that are currently available from NGS web services. These different heights could lead to confusion if users are not careful. Most users won’t be using the experimental geoid interactive web service to compute an estimate of an orthometric height but all users should provide the appropriate metadata to avoid any confusion.
Different Height Values for Station E 116 (PID GA0589)
Chart: National Geodetic Survey
The hybrid geoid model GEOID18 is currently being developed and is not ready to be published, but there is a web page that highlights that it will replace GEOID12B in early 2019 [see box titled “Hybrid GEOID18 Website“] GEOID18 values will be similar to GEOID12B because both hybrid geoid models are made to be consistent with published NAVD 88 values. Saying that, there will be differences especially in areas where the GPS on BMs program identified stations that have moved since the last time they were leveled and, therefore, they were not used in GEOID18.
My last column provided an update and status report on stations observed in support of the 2018 GPS on BMs program. Many stations with potential invalid published orthometric heights have been identified by the GPS on BM program. This information will be very useful to the surveying and mapping community as well as to NGS. Once NGS publishes the next hybrid geoid model, GEOID18, OPUS results will probably provide an estimate of the NAVD 88 orthometric height computed using GEOID18 similar to what it does now using GEOID12B. In my opinion, the results of GEOID18 will be better than GEOID12B in most areas of the United States and will be helpful in identifying stations that have moved since they were last leveled.
NGS’ official date for accepted data for inclusion in the next hybrid geoid model, GEOID18, ended September 21, 2018. Continuing to submit your results to OPUS Shared will provide a way for others to analyze the results to determine whether a station has an issue that requires attention. New OPUS shared results will be very useful for evaluating the reliability of the model. After the hybrid geoid model, GEOID18, is published, NGS’ GPS-on-Bench-Mark Program will expand to include other regions and will focus on data to improve NGS datum transformation tools. Further columns will address differences between GEOID12B and GEOID18 after GEOID18 officially replaces GEOID12B.
