U-blox has released its tiny EVA-M8Q high-sensitivity GNSS module in a 7 millimeter by 7 millimeter package. EVA-M8Q supports GPS, GLONASS, BeiDou and Galileo, the company said in a news release.
The EVA-M8Q completes the company’s lineup of receivers in the miniature and EVA form-factor package.
The EVA-M8Q is TCXO-based and is optimized to provide the highest acquisition and tracking sensitivity, the company says, making it suitable for use with small antennas either in covert applications such as asset tracking and stolen vehicle recovery, or in portable devices; the previously announced EVA-M8M is better suited to cost-sensitive systems.
“The key differentiator of the EVA-M8Q to the other cost effective EVA variants is the sensitivity,” says Stéphane Vincent, product strategy director, positioning, u-blox. “This, along with the accuracy provided by concurrent reception of three GNSS constellations, enables an end-system and its antennas to be easily hidden within a vehicle or other high-value asset that need to be tracked.”
The ease of manufacturing offered by the Quad Flat No-leads (QFN)-like package suits requirements for medium- to high-volume production. While the highly integrated module of the EVA-M8 series allows OEMs to achieve a faster time-to-market.
EVA-M8 series are the smallest u-blox modules featuring GPS, BeiDou, Galileo and GLONASS reception. Three out of the four GNSS constellations can be received concurrently, which leads to high positioning accuracy. The series also features anti-spoofing and anti-jamming technology to provide superior security and integrity protection.
Samples of the EVA-M8Q are available now. The modules will be in full production in Q4 2016.
Features
Complete GNSS solution in 7 millimeter by 7 millimeter package.
Sensitivity — ideal for small or covert installations.
High accuracy from three concurrent GNSS.
Highly integrated module leads to faster time-to-market.
Harxon has released a mini base radio — HX-DU8609T — designed for customers who want to quickly set up a local data-transfer network.
HX-DU8609T is a versatile data radio providing a flexible solution for applications that require reliable data transfer, low cost, small size and rugged construction. It has a wide (60-Mhz) bandwidth that covers 410-470 MHz combined with an IP67 sealed housing, suitable for harsh environment conditions such as driving tests, construction equipment and precision farming.
The sophisticated 5-10 Watt mini base radio is compatible with existing Harxon modems and other products, the company said. Both 12.5- and 25-kHz channel widths are software-selectable. Output of more than 10 Watts enables long connection distances.
The HX-DU8609T is equipped with a DB9 connector, digital tube, LED and keypad, used to indicate the current operating status as well as for changing the operating channel and power level of the radio modem.
To save on registration rates for ION GNSS+ 2016, the 29th annual meeting of the Institute of Navigation Satellite Division, complete your early bird registration by Friday, Aug. 12.
If you book your hotel room for ION GNSS+ 2016 before you register, you will receive $200 off your conference registration. To qualify for the discount, enter your hotel confirmation number from the Hilton Portland & Executive Tower, The Quality Inn Downtown Convention Center or the Courtyard by Marriott Portland Downtown/Convention Center at the start of the registration process. You will need your valid hotel confirmation from one of these official ION GNSS+ hotels to claim the discount during registration.
Keynote Address: The Positioning System of the Brain
Join Professor John O’Keefe, winner of the Nobel Prize in Physiology and Medicine for the discovery of cells that constitute a positioning system in the brain, as he explains how animals and humans find their way and the “cognitive map” that forms the framework for identifying where you are, where other things are in your environment and how to get from one place to another.
30th Anniversary Celebration
Celebrate 30 years of ION GPS, ION GNSS and ION GNSS+ with a 1980’s style celebration, featuring the decade’s best food, games and music. 1980’s dress is encouraged; raffle tickets for prizes will be given to those who attend in costume. This event is included with all registrations.
A team of Rohde & Schwarz engineers have found a new way to hack Pokémon Go, the massively popular app that debuted last month.
The engineers are generating GNSS data with a Rohde & Schwarz signal generator, and feeding the signal directly into the mobile device, making it possible to collect dozens of Pokemon right in the lab.
The team produced a video showing the hack, which has received almost 400,000 views on YouTube, and received coverage from Bloomberg and The Verge.
The Munich-based Rohde & Schwarz team provides the following hardware diagram of the setup:
The team also describes the technical details:
“The setup is a little proof of concept by simulating GPS signals with an HIL — hardware in the loop — interface, which can also be used for a flight simulator or similar applications.
“A R&S-SMBV100A vector signal generator serves as a source to simulate real-life GNSS RF signals. We use a custom PC software with a joystick controller for the ultimate gaming experience *wink* — it may as well be controlled with a mouse. This software streams HIL commands to the signal generator over a LAN interface and interpolates position and velocity changes. The interpolation will be done according to a desired inertia model — pedestrian/car/plain — we actually used a slow car here with a maximum speed of ~15km/h. This is useful, for instance, if you assume that cars will not make 90° turns.
“We set the GNSS coordinates of the signal generator to some arbitrary position in the world and start the HIL mode — this will result in a ban if you jump quickly from Moscow to Sydney! You have to wait a reasonable amount of time in between.
“The signal generator simulates a real-life GNSS RF signal, which is fed indirectly into the mobile phone and to a u-blox M8 GNSS receiver. This is why we use an RF splitter. The losses from antenna to device are roughly 30 dB. We therefore generate a signal of -80 dBm in order to achieve the common GNSS signal strength of -110 dBm at the device. The idea behind the shielding box is to protect the device from the signal from outside. You could also build the setup in a cellar.
“We use the corresponding u-center v8.11 software, which is connected to the GNSS receiver to visualize our current position using a Google Maps plug-in. The u-blox is connected via USB to the computer.
“By doing so, we create a closed-loop realtime GNSS simulation with user feedback and interaction.”
Clarion has adopted Furuno’s GV-86 in the NXR16 for in-car navigation and positioning. Clarion is a Japanese manufacturer of in-vehicle infotainment head units, including car navigation systems and car audio systems.
Clarion thoroughly evaluated the Furuno receiver for its robustness in heavy-use environments and the company’s long-term supply-chain capability.
The NXR16, which debuted in June, is designed to fill the needs of professional-use customers in the auto-leasing and rent-a-car industry. It supports multi-language and multi-display features that satisfy the increasing number of foreign tourists using rental-cars.
Clarion’s NXR16 car navigation system.
Furuno’s GV-86 is a dead-reckoning-enabled GNSS receiver that concurrently receives GPS, SBAS and QZSS satellite signals. Its dead-reckoning function enables it to provide high-accuracy positioning in environments where no GNSS signals can be received, such as tunnels, underground car parking and deep urban canyons.
The dead-reckoning function is realized by integrating the information from a gyro sensor and a velocity sensor.
Rockwell Collins is bringing its NavFire Precision Positioning Service (PPS) GPS to Leonardo-Finmeccanica’s Vulcano family for naval and artillery applications.
NavStrike military GPS offers high performance GPS for tightly coupled GPS/INS integrations.
Derived from the field-proven 12-channel NavFire Precise Positioning Service GPS receiver, Rockwell Collins’ NavStrike military GPS offers high performance GPS for tightly coupled GPS/inertial navigation system (GPS/INS) integrations.
“We have customized the NavFire receivers for the particular caliber of the ammunition, and provided full support to the customer during and after the firing trials,” said Claude Alber, vice president and managing director, Europe, Middle East and Africa for Rockwell Collins. “In the end, our product perfectly matched the demanding performance requirements of our customer.”
The NavFire GPS includes the Selective Availability Anti-Spoofing Module (SAASM) to allow decryption of precision GPS observations through over-the-air rekeying. The positioning information is used by the guidance system of the projectile.
Nearly 30 years ago, Rockwell Collins assisted the U.S. Air Force in developing GPS technology and that legacy continued when the company created the world’s first all-digital miniature GPS receiver under contract with DARPA. Over the years, Rockwell Collins has produced more than 50 GPS products and delivered more than 1 million GPS receivers for commercial avionics and government applications. This recent GPS contract continues this legacy to create leading edge military navigation solutions.
A: Solving for jamming, intentional or unintentional, in the design of any GNSS technology platform is no longer an option. How much any one company spends is largely a function of how much is spent on engineering overall and of how much has already been invested upfront on jamming mitigation. The required level of jamming resistance of any PNT solution also depends very much on the particular application, which in turn influences the budget allocated.
A: GNSS jamming is a growing concern, and an assessment of risks and an element of testing against the most applicable real world threats should be included as part of every developer’s engineering process. Spirent has decades of experience in providing test equipment and services to engineers working to understand and mitigate jamming threats. We have seen increased investment by designers and integrators of PNT systems that are driven to provide robust/resilient solutions to their customers.
A: While some receivers already incorporate jamming protection (e.g., CW excision), more sophisticated methods (for example, against broad-band jamming and spoofing) should be incorporated into perspective products. The percentage of R&D budget depends on a line of business. For manufactures pursuing applications such as military and critical infrastructure, the number can be as high as 50 percent. For many civilian applications a potential impact of jamming is less damaging. Yet, from 10 percent to 20 percent should be still allocated.
Pointer Telocation Ltd. – a developer, manufacturer and operator of Mobile Resource Management (MRM) — signed a contract July 18 with CET RIO (the Rio de Janeiro Transit Authority) to provide technology and integration services during the 2016 Olympic Games, managing the vehicles and personnel responsible for transit control, emergency and contingencies.
More than 200 vehicles will be monitored in real time which will be managing, controlling and supporting the traffic management systems starting Aug. 5 and throughout the games.
The system will use Pointer’s Web Fleet Software Platform and will be integrated into the CET Control Center as well as the COR (the city’s Operation Center), providing a unified view of traffic information throughout Rio.
“We are very pleased to be playing an important role in the smooth running of the Olympic Games this summer,” said David Mahlab, chief executive officer of Pointer. “Our selection by Rio’s Transit Authority for this very high profile event and mission critical task, demonstrates a strong level of trust in our solution. We look forward to successfully delivering on this contract, and we believe this will provide us with very strong references for further work in the region.”
The Air Force has released a Request for Proposal (RFP) for launch services for the GPS III-3 mission, scheduled to launch in 2019. Proposals are due Sept. 19; the contract will be a standalone contract for a single GPS III launch.
The United Launch Alliance (ULA) and SpaceX are expected to compete for the contract. In April, SpaceX was chosen to launch the GPS III-2 satellite in May 2018. ULA chose not to compete.
The RFP seeks an Evolved Expendable Launch Vehicle (EELV) Launch Service. The draft RFP was released on June 14 to obtain industry feedback to inform the Final RFP. After extensive industry engagements, the Final RFP was released on Aug. 3 with proposals due back to the Air Force no later than Sept. 19 in accordance with the solicitation instructions.
After evaluating proposals through a competitive, best-value source selection process, the Air Force will award a firm-fixed price contract that will provide the government with a total launch solution including launch vehicle production, mission integration and launch operations for the GPS III-3 satellite.
Artist’s concept of the nextgen GPS III satellite (courtesy of the USAF).
The Air Force’s acquisition strategy for this solicitation achieves a balance between mission success/operational needs, and lowering launch costs, through reintroducing competition for national security space missions, the Air Force said in a press release.
“Launch system certification is a key element (high technical bar) within this solicitation to provide insight into the technical capabilities and rigorous processes that demonstrate a launch vehicle contractor’s ability to design, develop, manufacture, and launch national security space missions and contributes to the overall flight worthiness process,” said Lt. Gen. Samuel Greaves, Space and Missile Systems Center commander and Air Force program executive officer for Space. Prior to contract award, the contracting officer will verify that the Offeror has a certified launch system as part of a responsibility determination resulting in a high technical bar.
“Through this competitive solicitation for GPS III launch services, we hope to continue fostering competition in order to promote innovation and reduce cost to the taxpayer while maintaining our laser focus on mission success,” Greaves said.
GPS III is expected to provide improved anti-jamming capabilities as well as improved accuracy for precision, navigation, and timing. It will incorporate the common L1C signal which is compatible with the European Space Agency’s Galileo global navigation satellite system and compliment current services with the addition of new civil and military signals.
The first GPS III satellite undergoes system-level thermal vacuum testing. (Photo: Lockheed Martin)
This is the second competitive launch service solicitation under the current Phase 1A procurement strategy. The Phase 1A procurement strategy reintroduces competition for national security space launch services. Under the previous Phase 1 strategy, ULA was the only certified launch provider. In 2013, ULA was awarded a sole-source contract for launch services as part of an Air Force “Block Buy” of 36 rocket cores that resulted in significant savings for the government through FY 2017.
In May 2015, Space Exploration Technologies (SpaceX) was certified for EELV launches resulting in two launch service providers that are qualified to design, produce, qualify and deliver a launch capability and provide the mission assurance support required to deliver national security space satellites to orbit.
Geneq’s iSXBlue receivers are now fully compatible with Esri’s Collector for ArcGIS 10.4. for iOS, according to Geneq.
The high sub-metric accuracy which characterizes the iSXBlue receivers is thus available in real time for field workers and Collector users.
Users of the high-recision receivers can take advantage of new features of data collection with the Collector software, particularly:
Detailed information about the location and its related accuracy
An easy way of setting a minimal precision value during data collection
A new simple interface for Bluetooth connection setting with the iSXBlue receiver
New correction profile setting to define datum transformations
Capture GNSS metadata (accuracy, correction type, DOP,…) and attach it to features you collect
Improved notifications for receiver changes or configuration issues
Users that need centimeter accuracy can use Geneq’s iSXBlue RTN software, available at the Apple App Store. iSXBlue RTN allows users to receive and use RTK corrections via an Internet Protocol (IP) connection (NTRIP or DIP) along with iSXBlue receivers.
TerraGo Edge 3.9.5 is now out. The new version offers a number of new, powerful features for iOS, Android and web users, the company announced.
TerraGo Edge is a mobile platform that combines customizable smart forms and workforce management with advanced GPS and GIS features for fast, accurate asset inspections, field surveys, site audits and mobile data collection projects.
“Quality management guides everything we do and the newest version of TerraGo Edge will help us eliminate data entry errors and capture mobile inspection data efficiently and correctly the first time,” said Matthew Colvin, junior team lead, Corrosion Service. “TerraGo’s agile development teams have worked together with us, listened to our ideas and rapidly turned them into valuable features, versus waiting months or years for a new version. For our fast-paced engineering projects, this translates directly into continuous quality improvement, service innovation and successful projects for our customers.”
“We work closely with our customers as part of our agile development process so we can deliver customer-driven innovation with each and every release of TerraGo Edge,” said Dave Basil, vice president of product development at TerraGo. “In this release, we were able to provide measurement tools and quality assurance features that we think are the best in the market. It’s not because we designed them internally, but based on the assessment of our end users, who tested them under real-life working conditions and gave us the feedback and insights you can’t get from sitting at a keyboard, allowing us to design the optimal user experience.”
Upcoming Survey Scene newsletters will carry additional columns in this series.
Basic procedures and tools for determining valid published NAVD 88 GNSS-derived orthometric heights for constraints
These columns have provided the reader with basic concepts, routines and procedures for understanding, analyzing, evaluating and estimating GNSS-derived ellipsoid and orthometric heights.
In my last column, Part 7 (June 2016), we analyzed the changes in adjusted heights due to different leveling-derived NAVD 88 height constraints and compared the results with the published NAVD 88 leveling-derived orthometric heights. My column demonstrated how every constraint has an influence on the final set of adjusted heights.
As mentioned in previous columns, when incorporating new geodetic data into the National Spatial Reference System (NSRS), it is important to maintain consistency between neighboring stations. If the station has moved since the last time its height was established then not constraining the published value and superseding the height is the appropriate action to take. As I emphasized in Part 6 (April 2016), if the difference is not due to movement but due to some other reason such as the results of a previous adjustment distribution correction then superseding the height may not be the appropriate action to take. In Part 6, we looked at the network design of the NAVD 88 project and estimated the potential NAVD 88 distribution correction between two benchmarks involved in the original NAVD 88 general adjustment. It was also mentioned in the last newsletter that all of the analysis and recommendations have been based on using the latest scientific geoid model xGeoid15b.
However, in practice, GNSS-derived orthometric heights are incorporated into the NAVD 88 using the latest hybrid geoid model, i.e., GEOID12B. I recommend first performing the analysis using the scientific geoid model because the hybrid geoid model has been warped to be consistent with the published NAVD 88 values. This was described in detail in my October 2015 newsletter. The analysis using the scientific geoid should be included in the project report especially if the user finds significant differences between the results using the two different geoid models. In my last column, I stated that “maintaining consistency between closely spaced stations is extremely important when incorporating data into an existing network. Based on the information so far and the results using GEOID12B, I would not recommend constraining the published NAVD 88 heights of stations PHANIEL and PLAZA in the final NAVD 88 GNSS-derived orthometric height adjustment. These two stations resulted in significant changes in relative adjusted heights when they were constrained. (See Part 6.)”
It was also noted in a previous column (Part 5, February 2016) that 10 of the 2015 GNSS Rowan County Height Modernization project’s stations have published NAVD 88 GNSS-derived orthometric heights. These station are denoted as Height Modernization stations and are important because they are on the edge of the network where there’s a void of published NAVD 88 leveling-derived orthometric heights. In this newsletter, for these 10 stations we will look at the differences between their published NAVD 88 heights and their adjusted GNSS-derived orthometric heights from the Rowan County project.
First, we need to briefly look at one of the leveling-derived stations — Station PLAZA — that was identified as a potential outlier in Part 7. In that column, I provided the following information about station PLAZA:
The geodetic data and information for station PLAZA is listed below:
As described in Part 6 (April 2016), station PLAZA and station FIFTH have a large relative difference between the adjusted GNSS-derived orthometric height and the published NAVD 88 orthometric height value (-3.2 cm);
Four other stations in the vicinity have small relative differences between the adjusted GNSS-derived orthometric heights and the published NAVD 88 orthometric heights values, 37 DRD (0.6 cm), Midtown (-0.1 cm), Midway (1.0 cm), and J 181 (1.1 cm) — indicating a problem with station PLAZA;
Station FIFTH and PLAZA are only 400 meters apart, and their adjusted heights were established in two different adjustments: station FIFTH was leveled in 2013 (adjustment date of March 2015) and station PLAZA was leveled to in 1989 (adjustment date of September 1997) — indicating a potential inconsistency between adjustments;
PLAZA’s datasheet states that “the station was recovered as described in 2012 except the area between the curb and sidewalk has been filled with concrete. Mark is now part of the sidewalk but does not appear to have been disturbed.”
Based on the available information to date, I would not recommend constraining the published height of station PLAZA in the final adjustment. Once again, this station’s published height should not be superseded by the GNSS project until new leveling has been performed between station FIFTH and PLAZA.
As I mentioned, Station PLAZA’s published height should not be superseded by the GNSS project until new leveling has been performed between station FIFTH and PLAZA. Well, ask and you will receive. Gary Thompson, the director of the North Carolina Geodetic Survey, had one of his field crews, which was in the area, relevel the section between station FIFTH and PLAZA. The newly leveled results changed the leveling-derived height of PLAZA relative to FIFTH by 3.5 cm. The new leveling-derived orthometric height of PLAZA now agrees with the GNSS-derived orthometric height to within a centimeter.
This means that the published height of PLAZA should not be constrained in the final adjustment and should be superseded by the GNSS-derived orthometric height. If the leveling data is submitted to NGS for inclusion into the NAVD 88, then the NAVD 88 height resulting from the new leveling data should be constrained in the final adjustment.
Now, let’s look at the 2015 GNSS Rowan County Height Modernization project’s stations that have published NAVD 88 GNSS-derived orthometric heights. The user can identify stations that have been established following NGS Height Modernization procedures by looking at NGS datasheets. The datasheets for Height Modernization stations have the following statement at the top of the datasheet: “This is a Height Modernization Survey Station.” In addition to that statement, the NAVD 88 orthometric height is published to the centimeter level with the attribute code of “GPS OBS.” (See the example titled “Excerpt from the NGS Datasheet for Station GOODMAN.)
Excerpt from the NGS Datasheet for Station GOODMAN
1 National Geodetic Survey, Retrieval Date = JULY 2, 2016
DL9977 ***********************************************************************
DL9977 HT_MOD – This is a Height Modernization Survey Station.
DL9977 DESIGNATION – GOODMAN
DL9977 PID – DL9977
DL9977 STATE/COUNTY- NC/STANLY
DL9977 COUNTRY – US
DL9977 USGS QUAD – GOLD HILL (1983)
DL9977
DL9977 *CURRENT SURVEY CONTROL
DL9977 ______________________________________________________________________
DL9977* NAD 83(2011) POSITION- 35 30 06.47415(N) 080 15 37.24680(W) ADJUSTED
DL9977* NAD 83(2011) ELLIP HT- 171.358 (meters) (06/27/12) ADJUSTED
DL9977* NAD 83(2011) EPOCH – 2010.00
DL9977* NAVD 88 ORTHO HEIGHT – 201.76 (meters) 661.9 (feet) GPS OBS
DL9977 ______________________________________________________________________
DL9977 NAVD 88 orthometric height was determined with geoid model GEOID09
DL9977 GEOID HEIGHT – -30.377 (meters) GEOID09
DL9977 GEOID HEIGHT – -30.402 (meters) GEOID12B
DL9977 NAD 83(2011) X – 879,427.184 (meters) COMP
DL9977 NAD 83(2011) Y – -5,123,507.841 (meters) COMP
DL9977 NAD 83(2011) Z – 3,683,429.929 (meters) COMP
DL9977 LAPLACE CORR – 1.70 (seconds) DEFLEC12B
DL9977
DL9977 Network accuracy estimates per FGDC Geospatial Positioning Accuracy
DL9977 Standards:
DL9977 FGDC (95% conf, cm) Standard deviation (cm) CorrNE
DL9977 Horiz Ellip SD_N SD_E SD_h (unitless)
DL9977 ——————————————————————-
DL9977 NETWORK 0.41 0.80 0.18 0.15 0.41 -0.01103221
DL9977 ——————————————————————-
DL9977 Click here for local accuracies and other accuracy information.
DL9977
The procedures for analyzing the published NAVD 88 GNSS-derived orthometric heights are the same as those used to analyze the NAVD 88 leveling-derived orthometric heights. These procedures and routines have been documented in my previous columns. There is, however, one major difference between incorporating new leveling data into NAVD 88 and incorporating new GNSS data into NAVD 88. That is, when a station gets superseded in a leveling network adjustment due to previous adjustment distribution corrections, to maintain consistency the older leveling data in the area are readjusted to be consistent with the newly observed leveling data and latest published adjusted heights.
An adjustment distribution correction from the NAVD 88 general adjustment was discussed in the Part 7 (See Figure 6, “An Example of an Estimate of the NAVD 88 Distribution Correction Between two Stations Established with Old Leveling Data and Large Loops.”). So, what’s the difference?
Both NAVD88 leveling-derived orthometric heights and GNSS-derived orthometric heights are based on adjustments constraining NAVD 88 published orthometric heights. However, GNSS-derived orthometric heights are also computed using the latest NGS hybrid geoid model. If a station’s GNSS-derived orthometric height gets superseded, the previous GNSS data are not readjusted to be consistent with the latest observations and published heights. Once again, if the station physically moved then superseding the height is the appropriate action and there is no requirement to readjust the older GNSS data.
However, if the station did not physically move then the new published height may be inconsistent with its neighboring stations. I’m not saying that this is right or wrong, I’m only mentioning it so the user considers this information in their analysis.
The procedures outlined in NGS’ NGS 59 document, which was discussed in Part 5, were developed to minimize the effect due to different geoid models and superseded heights. (See excerpt titled “Four Basic Control Requirements for Estimating GNSS-Derived Orthometric Heights.”) The requirements include surrounding the project with valid NAVD 88 benchmarks and, if necessary, enlarging the project area to occupy enough leveling-derived benchmarks. The intent of these requirements are to help control any small relative differences between previously published hybrid geoid models. It should be noted that some of the latest hybrid geoid models are significantly different the older hybrid geoid models.
Therefore, when comparing a project’s adjusted heights with published NAVD 88 GNSS-derived orthometric heights, the user needs to consider which hybrid geoid model was used to establish the published GNSS-derived orthometric height. The NGS datasheet provides the hybrid geoid model and geoid height value used to establish the height. This was highlighted on the datasheet for station GOODMAN (see the example titled “Excerpt From the NGS Datasheet for Station GOODMAN). The statement NAVD 88 orthometric height was determined with geoid model GEOID09means that station GOODMAN’s GNSS-derived orthometric height was established in a GNSS project using the hybrid geoid model GEOID09. The question is, what’s the difference between GEOID09 and the latest hybrid model?
The datasheet provides the hybrid geoid model value used to establish the height (in this example, GEOID09 = -30.377 m) as well as the latest hybrid geoid model value (in this example, GEOID12B = -30.402 m). Based on station GOODMAN’s published datasheet, the difference is only 2.5 cm. This difference may be much larger in the mountains of North Carolina.
Four Basic Control Requirements
for Estimating GNSS-Derived Orthometric Heights:
Requirement 1: GNSS-occupy stations with valid NAVD 88 orthometric heights; stations should be evenly distributed throughout project.
Requirement 2: For project areas less than 20 km on a side, surround project with valid NAVD 88 benchmarks, i.e., minimum number of stations is four; one in each corner of project. [NOTE: The user may have to enlarge the project area to occupy enough benchmarks, even if the project area extends beyond the original area of interest.]
Requirement 3: For project areas greater than 20 km on a side, keep distances between valid GNSS-occupied NAVD 88 benchmarks to less than 20 km.
Requirement 4: For projects located in mountainous regions, occupy valid benchmarks at the base and summit of mountains, even if the distance is less than 20 km.
Station BLACK BEAR, located in the mountains near Asheville, North Carolina, is an example of a significant difference between GEOID09 and GEOID12B; the difference is -14.9 cm. (See the example titled “Excerpt from the NGS Datasheet for Station BLACK BEAR.) This may not be a problem if all stations in the area are effected by the same difference but that’s not the case in this area.
Station BUCK is a nearby station (about 11 km away from BLACK BEAR) and according to the NGS database “mark_source option”, stations BLACK BEAR and BUCK were involved in the same GNSS project so their GNSS-derived orthometric heights most likely were established in the same adjustment project. [NOTE: The use of the “mark_source” option of the NGS datasheet was described in Part 7.] The GEOID09 and GEOID12B difference at station BUCK is 1.0 cm. The relative difference in hybrid geoid models between stations BLACK BEAR and BUCK is almost 16 cm.
Excerpt from the NGS Datasheet for Station BLACK BEAR
PROGRAM = datasheet95, VERSION = 8.9
1 National Geodetic Survey, Retrieval Date = JULY 26, 2016
DM2549 ***********************************************************************
DM2549 HT_MOD – This is a Height Modernization Survey Station.
DM2549 DESIGNATION – BLACK BEAR
DM2549 PID – DM2549
DM2549 STATE/COUNTY- NC/YANCEY
DM2549 COUNTRY – US
DM2549 USGS QUAD – MT MITCHELL (1946)
DM2549
DM2549 *CURRENT SURVEY CONTROL
DM2549 ______________________________________________________________________
DM2549* NAD 83(2011) POSITION- 35 46 00.04321(N) 082 15 54.04248(W) ADJUSTED
DM2549* NAD 83(2011) ELLIP HT- 1974.465 (meters) (06/27/12) ADJUSTED
DM2549* NAD 83(2011) EPOCH – 2010.00
DM2549* NAVD 88 ORTHO HEIGHT – 2004.48 (meters) 6576.4 (feet) GPS OBS
DM2549 ______________________________________________________________________
DM2549 NAVD 88 orthometric height was determined with geoid model GEOID09
DM2549 GEOID HEIGHT – -29.990 (meters) GEOID09
DM2549 GEOID HEIGHT – -29.841 (meters) GEOID12B
DM2549 NAD 83(2011) X – 697,556.510 (meters) COMP
DM2549 NAD 83(2011) Y – -5,135,618.055 (meters) COMP
DM2549 NAD 83(2011) Z – 3,708,370.482 (meters) COMP
DM2549 LAPLACE CORR – -6.14 (seconds) DEFLEC12B
DM2549
DM2549 Network accuracy estimates per FGDC Geospatial Positioning Accuracy
DM2549 Standards:
DM2549 FGDC (95% conf, cm) Standard deviation (cm) CorrNE
DM2549 Horiz Ellip SD_N SD_E SD_h (unitless)
DM2549 ——————————————————————-
DM2549 NETWORK 0.47 0.86 0.21 0.17 0.44 -0.05699591
DM2549 ——————————————————————-
DM2549 Click here for local accuracies and other accuracy information.
DM2549
Figure 1 is a contour plot of the differences between GEOID12A and GEOID09 in the area surrounding stations BLACK BEAR and BUCK. [NOTE: The ESRI raster plots are based on GEOID12A not GEOID12B. GEOID12A is identical to GEOID12B everywhere, except in Puerto Rico and Virgin Island region. Therefore, in North Carolina, GEOID12A is equivalent to GEOID12B.] Looking at the plot it is obvious that there is a significant difference between the two hybrid geoid models in this region of North Carolina. What does this mean to someone performing a new GNSS-derived orthometric height adjustment in the area? If they occupied station BLACK BEAR and compared their adjusted GNSS-derived orthometric height using GEOID12B to the NAVD 88 published GNSS-derived orthometric height that was established using GEOID09, they most likely will get a large residual due to the difference between the two hybrid geoid models. As previously mentioned in this newsletter, NGS’ NGS 59 guidelines were developed to minimize the effects of different hybrid geoid models, but in these extreme cases the procedures may not have been able to minimize the total effect. It is important for the user to understand the differences between the various published hybrid models and experimental geoid models being developed by NGS. This topic was discussed in detail in the October 2015 newsletter.
Figure 1. A contour plot of the differences between GEOID12A and GEOID09 in the area surrounding stations BLACK BEAR and BUCK.
Now, let’s look at the published NAVD 88 GNSS-derived orthometric heights occupied in the Rowan County Height Modernization project. Table 1 is a list of the stations occupied in the Rowan County project that have published NAVD 88 GNSS-derived orthometric heights. The table provides the hybrid geoid model value used to establish the published NAVD 88 height as well as the latest hybrid geoid model value, GEOID12B. Figure 2 is a contour plot of the differences between the GEOID12A and GEOID09 in the Rowan County Height Modernization project area. Looking at the plot, the user can see that most of the differences are all less than 3 cm between GEOID12A and GEOID09 in the Rowan County Project area.
Figure 2. A contour Plot of the differences between GEOID12A and GEOID09 in the Rowan County Height Modernization project area.
As we can see from Table 1, all of the differences between the two hybrid geoid models are less than or equal to 2.5 cm. (See highlighted rows and column in Table 1.)
Figure 2 plots the adjusted GNSS-derived orthometric height (using GEOID12B) from a minimally constrained adjustment minus the published NAVD 88 GNSS-derived orthometric heights. Most of the differences are less than 3 cm which for some stations could be a result of the difference hybrid geoid models to establish the published GNSS-derived orthometric heights.
Looking at figure 2, almost all of the differences between the GNSS-derived orthometric heights (using GEOID12B) from the minimum-constraint least squares compared with the published NAVD 88 GNSS-derived orthometric heights are less than 3 cm. No station appears to be an obvious outlier. The fact that all differences except for one are negative is interesting and is worth investigating at a later date. More analysis will need to be performed to understand if this is significant or not. Table 2 provides the adjusted GNSS-derived heights from a minimally constrained adjustment minus the published heights (both ellipsoid and orthometric).
The last item to look at is a comparison of the adjusted heights from a constrained adjustment where all valid published leveling-derived heights were constrained. Figure 3 and Table 2 provide the constrained adjustment results (where all of leveling-derived published heights except for the 3 suspect heights were constrained) compared with the published NAVD 88 GNSS-derived orthometric heights. All of the differences are less than +/- 2 cm except for station NATHAN which is -2.1 cm. All of the relative differences of closely-spaced stations are less than 2 cm and most are less than 1 cm. This means constraining these stations should not adversely influence the unconstrained stations. Note that after constraining the published NAVD 88 leveling-derived heights, the negative bias is gone but the differences do not appear to be random. That is, the northern stations are all negative and the southern stations are positive (See figure 3).
Figure 3. A plot of the constrained adjustment results (where all of leveling-derived published heights except for the 3 suspect heights were constrained) compared with the published NAVD 88 GNSS-derived orthometric heights.
These newsletters have focused on procedures and routines for establishing GNSS-derived orthometric heights. There are many ways to analyze and investigate GNSS data and adjustment results. I have provided some basic concepts that I believe are important for users to understand. The selection of constraints is a very important part of establishing accurate and consistent NAVD 88 GNSS-derived orthometric heights. It is just as important to document all decisions and results so others know how the published heights were established. NGS has a prescribed set of data and information that are required when submitted data for inclusion into the NSRS. This information is available from the NGS website (see section titled “MATERIALS NEEDED TO SUBMIT FOR THE PROJECT” in the document “adjustment_guidelines.pdf.”). We will address submitting the results in future columns.
In my next column, I will focus on the NGS GPS on BMS (GPSBM) dataset. This is the dataset used to create the hybrid geoid models; I mentioned this in Part 3. As mentioned in Part 3, the hybrid geoid model is designed to fit the published NAVD 88 leveling-derived orthometric heights. This file can be used to identify potential issues in the NAVD 88 network. GNSS users should be familiar with this dataset and how it can be useful to their analysis. My next column will address this topic.
U-blox has released its tiny EVA-M8Q high-sensitivity GNSS module in a 7 millimeter by 7 millimeter package. EVA-M8Q supports GPS, GLONASS, BeiDou and Galileo, the company said in a news release.
