Three years ago, engineering survey company G & C Sadlier Design was engaged to perform a route selection and centerline pegging survey for a gas pipeline duplication between Somerton in Victoria and Young in New South Wales, Australia. To accomplish the work, G & C Sadlier Design turned to FOIF GNSS receivers.
So far, about 225 kilometers have been surveyed and constructed, with 306 kilometers still to be surveyed, designed and built, according to surveyor Greg Sadlier. The current focus is a 100-kilometer section in Victoria and a 70-kilometer section in New South Wales. Recently completed are two linear static control surveys over 80 kilometers in Northern Victoria and 70 kilometers at the end of the project near Young in New South Wales.
“These surveys have been done using a FOIF F60 Base GNSS receiver and two FOIF A30 Rover receivers. (Two one-man survey crews are used),” Sadlier said. The procedure is to set up the F60 base over a point with known coordinates and elevation, approximately in the center of the alignment to be surveyed.
The base was set first, to record 1-second data to the datacard over the duration of the survey. One surveyor started the base, and surveyed forward to the end of the alignment, and the other rover crew started at the beginning of the alignment and surveyed towards the base. The rovers were also set to record 1 second data to the datacard.
“The control points were 0.75-m steel star pickets driven flush with the ground surface, and witnessed with a galvanized 1.5-m steel star picket,” Sadlier explained. “Each rover point was surveyed for 20 minutes plus 1 minute per kilometer of the distance to the base. That is, a point that is 35 Km from the base will be occupied for 55 minutes or 3300 epochs. With the control points at easy accessed positions, usually roads crossing the alignment, at intervals of about 8 kilometres mean that the survey of 80 Km is completed in one day.
“We have found the FOIF GNSS receivers are very easy to use, and the epoch readout on screen is very reassuring that the data is being stored, and easily confirms that the correct amount has been stored. The data is easily downloaded from the card and converted to Rinex format with FOIF RnxTransform. The data was post processed by a third party.”
The control survey results were adjusted (Helmert adjustment) onto check Permanent Marks at both ends. “This made a rotation of 0°00’00.001” and a shift of 0.007 meters E and 0.005 meter N. An elevation difference of .035 meters was manually adjusted out over the 80 kilometers,” Sadlier said.
“We are now using the control survey while surveying the route selection and features survey,” Sadlier said. “We have two RTK base locations at the 25-kilometer mark and 52-kilometer marks, and using our VHF radio solution have coverage over the entire job with a 10-kilometer overlap in the center.
“We have found that RTK observed control readings of 180 epochs return residuals of less than 010 meters for both coordinate and elevation for all the static control points. Very impressive results considering the length of the survey,” Sadlier said.
The engineering firm has yet to process the New South Wales data, but expects the same or better, Sadlier said, as the overall length is a little less and the surveyed control points were in more open country with less tree cover.
The Kenya Department of Surveys has acquired eight Spectra Precision Focus 30 total stations and an additional eight Epoch 50 GNSS receivers as part of an ongoing major effort to adjudicate land and prepare deeds, according to Spectra Precision.
Until recently, 67 percent of Kenya had yet to be adjudicated even as the work was supposed to be completed within 20 years after it was commissioned in 1957 by the British colonial government, according to the Lands Cabinet Ministry of Kenya. To rectify the problem, the government of President Uhuru Kenyatta two years ago began a major new push to produce three million titles by 2017. So far, the Land Surveys Department reports that 800,000 title deeds had been prepared and are being distributed.
Oakar Services Ltd., an East Africa geospatial firm, provided the consulting services that led to the Department of Land Survey’s purchase of the Spectra Precision total stations and GNSS receivers.
On the day of the solstice, June 21, geospatial professionals around the world and members of Land Surveyors United (a global support network for land surveyors) will be simultaneously recording survey-grade GPS data from thousands of points around the globe, to gain a more accurate understanding of the earth’s surface.
Measurements made on Survey Earth in a Day 4D (SEIAD) will serve as comparative data from prior events and to expand upon the database of logged points. “This year it will be called 4D, as we will be layering the data from our previous three years into a single map, representing points data gathered from thousands of locations around the planet by professional surveyors,” organizers said. “This day is the largest geospatial event in history as it allows surveyors to participate in their own location. With close to 3,000 more members than we had last year, we are hoping that all of you will participate from your location on June 21.”
In 2012 the first Survey Earth event was held, establishing many new understandings between geospatial and geomatics professionals and the general public on geospatial issues, organizers said. “With a mission not only to learn more about the Earth’s surface but also monitor its changes over time, and the changes in public perspective, as a global community, we may be more capable of assessing our future,” organizers said.
The conference will open with keynote speeches by Chris Cappelli (Esri Inc.) on “The Age of the Location Platform: How Mapping and GIS are Transforming the Work Environment” and Prof. Georg Gartner (TU Wien, Vienna University of Applied Sciences), president of the International Cartographic Association, on “The Future of the Map – the Map of the Future.”
“The agenda for the INTERGEO conference in Stuttgart is packed with exciting topics that are the focus of ongoing political debate on the digital world and will play a key role in shaping the way we work in future,” reads a statement by INTERGEO. “With keynote speeches and plenary talks delivered in English and simultaneous interpreting provided for one strand of the conference on the second day, it is clear that INTERGEO is also becoming increasingly significant on an international scale.”
The major topic of discussion at 2014’s INTERGEO remains a key part of the conference this year — INSPIRE examines geo-issues from a European perspective, providing practical examples and focusing on further development of the European directive. Other central themes include geodata as a basis for construction management and land development, a major concern for future development at regional and local level, as well as issues relating to property markets and valuation. These subjects are all crucial when it comes to discussing the “smart cities” and “smart villages” of the future, according to INTERGEO.
Another highlight of INTERGEO in Stuttgart this year will be the panel discussion on the second day on “Geospatial Information – A Key Element for Emerging Markets.” The high-profile panel of speakers include Bengt Kjellson (UN-GGIM Europe), Ola Rollen (Hexagon), Steve Berglund (Trimble) and Chris Cappelli (Esri Inc.).
A further key topic at the conference that is set to have a profound effect on the working world is geoinformation and mobility. DDGI and DVW will be addressing this together and discussing practical examples in two event strands.
The contributions on big data will focus on the rapid development of data capture, processing and presentation as well as the direct integration of data into business processes. Geoinformation as an element of networked processes is a subject of major international significance, as evidenced by the conference’s high-profile speakers. “In terms of digitization, the conference will be key to paving the path to Geospatial 4.0 and the networking of digital geodata,” said Prof. Karl-Friedrich Thöne, president of the event’s host, DVW, adding, “INTERGEO is the ideal forum for creating processes that could eventually benefit the entire value-added chain.”
As important as data may be in the digital world, it is also crucial to have the right visualization concepts in place. This will be demonstrated through presentations on the German Cartographers’ Day, which will form part of INTERGEO this year.
Together with free live technical support provided by practicing professional land surveyors via phone, email, message board and text messaging, JAVAD GNSS is pleased to announce the release of another innovative product, RAMS, Remote Assistance and Monitoring Services for J-Field software. J-Field is the field controller software developed for the TRIUMPH-LS GNSS receiver and the VICTOR-LS field controller. RAMS is currently available to all users of J-Field, JAVAD’s powerhouse software for survey data collection, stakeout, and computations.
With the J-Field enabled receiver/controller connected to the Internet (via internal GSM SIM card, Wi-Fi hotspot or Ethernet), users can make their receiver/controller accessible to JAVAD’s customer support team from anywhere in the world with three button presses. “It’s like having the support person looking over the user’s shoulder,” said Shawn Billings, a surveyor from Texas.
While the TRIUMPH-LS is connected to RAMS, the user and support person share control of the receiver, giving the support person the ability to make changes to settings on the receiver or train the user remotely. “It has changed the way support is conducted, making us more efficient at determining issues and more effective in training users,” said Billings. The connection is password-protected to ensure that only those intended have remote access to the receiver.
Beyond technical support, RAMS server access is available to the user community as well. This offers the ability for project managers to remotely supervise crew efforts in the field. Because operational control of the TRIUMPH-LS/VICTOR-LS is shared between the server user and the field user, the server user (project manager) could perform the more complex operations of land surveying, such as COGO calculations and localizations, as necessary, and then allow the field user (crew member) to continue the more routine tasks of data collection.
Should the task be simpler to accomplish with office software, RAMS allows file transfer directly from the LS to the server user’s own computer and vice versa, thus enabling the project manager to easily export points, linework (dwg, dxf, shape), vectors, photos and other project-related data from the LS to his desktop. From there, he can manipulate the data in his desktop application and then copy files, with newly computed coordinates or linework, back to the LS for the crew to work with in the field. In this way, RAMS uniquely supports the obligation surveyors have to exert responsible charge over their field crews.
The full receiver control, the access to receiver files, the robust RTK features of the TRIUMPH-LS and the fully customizable collection settings in J-Field make site monitoring possible as well.
RAMS server can be accessed with almost any device with an Internet browser and Internet access. “I’ve used RAMS server to assist customers from my desktop computer, laptop, android tablet and even my cell phone,” Billings added. “Using JAVAD’s RAMS server requires no installation of software on the remote device, only an Internet connection and web browser.”
For those wanting to operate RAMS on their own server, the RAMS Server application is available from JAVAD GNSS. An Android version of RAMS Server is also available, allowing users to connect an Android device directly to the TRIUMPH-LS without the need for an Internet connection. RAMS for Android creates a local network between the Android device and the LS and allows a field user to see and manipulate J-Field with the Android device should it be necessary to work with the LS beyond the reach or view of the user.
For more information on RAMS, J-Field, TRIUMPH-LS, VICTOR-LS and other JAVAD GNSS solutions, visit www.javad.com, email [email protected] or call 408-770-1770.
Editor’s Note: This month, we introduce a column by David B. Zilkoski, one of our two new Survey Scene editors. Zilkoski has worked in the fields of geodesy and surveying for more than 40 years, including serving as director of the National Geodetic Survey. See his full bio at the end of this article. He is joined by coeditor David Doyle, who contributed the May column.
The Three Types of Heights Involved in Computing GNSS-Derived Orthometric Heights
By David B. Zilkoski
David B. Zilkoski
This column is the first in a series of newsletters discussing issues associated with establishing orthometric heights using GNSS. The purpose of my columns is not to promote a particular procedure or process, but to provide the reader with information and analysis tools to consider when using GNSS to estimate orthometric heights.
This information is not new. During the past two decades, I have written several articles and papers on estimating GNSS-derived orthometric heights and presented numerous seminars describing guidelines on how to estimate GNSS-derived heights. However, due to the automation of technology and “blackbox” processes, many users are accepting results without performing the proper analysis to ensure that their results are reasonable and correct. These processes and procedures are not difficult to perform, but they can be very beneficial to obtaining an understanding of the accuracy of your results and ensuring your results are correct.
To understand how to estimate GNSS-derived orthometric heights at centimeter-level accuracy, you must have a basic understanding of the types of heights involved, how these heights are defined and related and how accurately these heights can be determined. In other words, you need to obtain a basic understanding of ellipsoid, geoid and orthometric heights and how they are related and their estimated accuracies.
To adequately address these topics, a series of Survey Scene newsletters will be separated into several sections. Some of this material will be a review (and probably boring) for those of you that have been performing GNSS-derived orthometric height surveys but, hopefully, you will gain a little benefit from the review. For those of you just starting out, I hope this will whet your appetite to obtain a better understanding of heights.
The following is a brief outline of what the columns will address:
Description of the three types of heights involved in computing GNSS-derived orthometric heights. That is, the definition of ellipsoid, geoid and orthometric heights, and how they are related. The user should understand what potential issues can arise due to how each height was defined, modeled and published. For example, in the United States, what errors exist in the published NAVD88 heights due to the leveling network design and remaining systematic errors in the leveling data? Constraining a North American Vertical Datum of 1988 (NAVD 88) published height that’s less accurate than your GNSS-derived orthometric height may allow your results to be consistent with the surrounding published heights, but could be distorting the rest of your results. In the end, you may need to do that, but you should know how your decision has influenced the rest of your results. I was the NAVD 88 project manager, so I know where all the problems are hidden. I am just kidding about knowing where all the problems are hidden, but there are issues associated with performing a nationwide network adjustment. NGS’ latest scientific geoid models can be useful in identifying potential issues in NAVD88.
Basic procedures for detecting published NAD 83 (2011) ellipsoid height outliers and how repeatability does not mean accuracy. Why you can’t assume that the published ellipsoid heights between two closely spaced stations is accurate to the published formal errors.
A description of the differences between a scientific gravimetric geoid model and a hybrid geoid model, and why it is important to use both geoid models in your analysis. The latest NGS hybrid geoid model, Geoid12B, is made consistent with the published NAVD 88 heights. This means you will be consistent with NAVD 88 when using GEOID12B to estimate GNSS-derived orthometric heights. However, this doesn’t guarantee that your GNSS-derived orthometric heights are accurate. NGS’s new beta experimental geoid height model xGEOID14B is not distorted to fit the published NAVD 88 heights, so it is useful for identifying valid NAVD 88 benchmarks.
Basic procedures for validating NAVD 88 height constraints used to estimate GNSS-derived orthometric heights. How to ensure your monuments haven’t moved since their last survey, and how good are your leveling-derived orthometric height constraints? Based on all available information and data, basic procedures to determine how good the final set of GNSS-derived orthometric heights really are. NGS 59 guidelines outline basic rules and procedures that need to be adhered to for computing accurate NAVD 88 GNSS-derived orthometric heights.
A description of NGS’ proposed 2022 Vertical Reference Frame and why it will be a good replacement for NAVD 88.
Background
Since 1983, NOAA’s National Geodetic Survey (NGS) has performed control survey projects in the United States using GPS satellites. NGS used these early GPS surveys projects to develop guidelines and procedures to estimate GPS-derived orthometric heights. These publications are known as NGS 58 and NGS 59.
Over the past three decades, GNSS surveying techniques have proven to be so efficient and accurate that they are now routinely used in place of classical line-of-sight surveying methods for establishing vertical control networks at the 2-cm level. Understandably, interest has been growing in using GNSS techniques to replace all leveling requirements. During the next decade, scientists will continue to develop better models and tools to facilitate GNSS-derived orthometric heights replacing classical line-of-sight surveying for many applications. In the meantime, it is important to have a clear understanding of the basic concepts of establishing GNSS-derived orthometric heights, otherwise water (or something worse) may not flow “down hill.”
Let’s start with a review of the three types of heights used when estimating GNSS-derived orthometric heights and how they are related.
Types of Heights and Their Relationship
Orthometric heights (H) are referenced to an equipotential reference surface, e.g., the geoid. The orthometric height of a point on the Earth’s surface is the distance from the geoidal reference surface to the point, measured along the plumb line normal to the geoid. These are the heights most surveyors have worked with in the past and are often called mean sea-level heights.
Ellipsoid heights (h) are referenced to a reference ellipsoid. The ellipsoid height of a point is the distance from the reference ellipsoid to the point, measured along the line that is normal to the ellipsoid. Years ago, the term ellipsoid height may have been a new concept to many traditional surveyors, but prevalent today because ellipsoid heights are readily derived from GNSS measurements.
At the same point on the surface of the Earth, the difference between an ellipsoid height and an orthometric height is defined as the geoid height (N). It should be noted that h=H+N is an approximate equation because H is measured along the plumb line normal to the geoid, where h is measured along a line normal to the ellipsoid (see Figure 1). For all practical survey projects, this small difference can be ignored.
Figure 1. Relationship of ellipsoid, geoid and orthometric heights.(Figure from POB article by David Zilkoski, The GPS Observer column, Feb. 28, 2001)
Several error sources that affect the accuracy of orthometric, ellipsoid and geoid height values are generally common to nearby points. Because these error sources are in common, the uncertainty of height differences between nearby points is significantly smaller than the uncertainty of the absolute heights of each point. This is the key to establishing accurate orthometric heights using GNSS.
Orthometric height differences (dH) can then be obtained from ellipsoid height differences (dh) by subtracting the geoid height differences (dN):
dH = dh – dN
Each of these heights and height differences have systematic errors that are accounted for by following appropriate procedures during data acquisition, by applying corrections based on environmental conditions and models, and/or estimating parameters using adjustment techniques. There will always be remaining errors that are not accounted for, and you must perform the appropriate procedures to detect, reduce or eliminate these errors in the final set of GNSS-derived orthometric heights.
Relative Accuracy Estimates
Adhering to NGS guidelines (NGS 58), ellipsoid height differences (dh) over short baselines (less than 10 km) can now be determined with 2 sigma uncertainties that are typically better than +/ 2 cm. The requirement that each baseline must be repeated and agree to within 2 cm of each other, and they must be repeated on two separate days, during different times of the day, should provide a final GNSS-derived ellipsoid height better than 2 cm at the 2-sigma level. The requirement that spacing between local network stations cannot exceed 10 km helps to keep the relative error in geoid height small.
Adding in the small error for the uncertainty of the geoid height difference and controlling the remaining systematic differences between the three height systems will produce a GNSS-derived orthometric height with 2-sigma uncertainties that are typically +/- 2 cm. Therefore, it is possible to establish GNSS-derived orthometric heights to meet certain standards, not millimeter standards, but 2-cm (95%) standards are routinely met now using GNSS.
When high-accuracy field procedures are used, orthometric height differences can be computed from measurements of precise geodetic leveling with an uncertainty of less than 1 cm over a 50 kilometer distance. Less accurate results are achieved when third-order leveling methods are employed. Depending on the accuracy requirements, GNSS surveys and present high-resolution geoid models can be employed as an alternative to classical leveling methods.
In the past, the primary limiting factor was the accuracy of estimating geoid height differences. With the computation of the more accurate National high-resolution geoid models, e.g., GEOID12A, the limiting factor is ensuring that the NAVD 88 orthometric height values used to control the project are valid. Strategically occupying benchmarks with GNSS that have valid NAVD 88 height values is critical to detecting, reducing or eliminating blunders and systematic errors between the three height systems. (Note: Valid NAVD 88 height values include, but are not limited to, the following: benchmarks that have not moved since their heights were last determined, were not misidentified, and are consistent with NAVD 88.)
Conclusion
This newsletter addressed the basic concepts of GPS-derived heights. To reiterate, it is important that you understand there are three types of heights involved with estimating GNSS-derived heights: ellipsoid, geoid and orthometric. Each of these heights has its own error sources that need to be detected, reduced or eliminated by following specific procedures or applying special models. This series of newsletter columns will address these potential errors sources and provide procedures to assist you in identifying these errors.
My next column in this series, coming in the August Survey Scene, will review guidelines for detecting, reducing or eliminating error sources in ellipsoid heights, and provide a brief discussion on using published NAD 83 (2011) ellipsoid heights in your analysis.
References
NOAA Technical Memorandum NOS NGS-58, Guidelines for Establishing GPS-derived Ellipsoidal Heights (Standards: 2 cm and 5 cm), Version 4.3.
NOAA Technical Memorandum NOS NGS-59, Guidelines for Establishing GPS-derived Orthometric Heights (Standards: 2 cm and 5 cm), are available. These guidelines address the establishment and densification of vertical control networks through the use of GPS surveys and valid NAVD 88 orthometric control.
David B. Zilkoski has worked in the fields of geodesy and surveying for more than 40 years. He was employed by National Geodetic Survey (NGS) from 1974 to 2009. He served as NGS director from October 2005 to January 2009. During his career with NGS, he conducted applied GPS research to evaluate and develop guidelines for using new technology to generate geospatial products. Based on instrument testing, he developed and verified new specifications and procedures to estimate classically derived, as well as GPS-derived, orthometric heights.
Now retired from government service, as a consultant he provides technical guidance on GNSS surveys; computes crustal movement rates using GPS and leveling data; and leads training sessions on guidelines for estimating GPS-derived heights, procedures for performing leveling network adjustments, the use of ArcGIS for analyses of adjustment data and results, and the proper procedures to follow when estimating crustal movement rates using geodetic leveling data.
If you are a professional land surveyor, we’d like to hear from you! Send us a brief account of how you use GNSS in your surveying work, what tips and tricks you can share with other surveyors, and what other hardware and software you are combining with GNSS to get the job done.
Submit around 300 words, although you can certainly go longer if you wish. Five winners will be chosen from the submissions received at [email protected]; winners will be chosen on the basis of clarity, liveliness, and, in some small measure, the unusual nature of the surveying tasks you perform or the way you go about them. Winners will receive $100 gift cards.
But we’re interested in hearing about straight run-of-the-mill jobs, too! Send your entries to [email protected]. Some entries may also be chosen for further development into articles for this newsletter, or GPS World magazine, or other publishing opportunities.
The CT4 and other rugged handhelds by Cedar Tree Technologies will now be available through Juniper Systems.
Juniper Systems is merging its subsidiary company, Cedar Tree Technologies, into Juniper Systems. The move will allow customers to purchase Cedar’s Android-operated rugged handhelds directly from Juniper Systems.
Juniper Systems launched Cedar Tree Technologies as a rugged handheld company in August 2014.
“With a reputation for top-of-the-line, ultra-rugged handheld computers, Juniper Systems aimed to expand its products to meet the needs of customers who may not need the outstanding level of ruggedness or support that Juniper handhelds provide. And that’s how Cedar Tree Technologies began. Cedar handhelds lie somewhere between consumer devices and Juniper Systems’ ultra-rugged handhelds, providing a mesh of both ruggedness and affordability,” said a statement from the company.
Cedar handhelds run on the Android operating system, offering access to thousands of business-ready apps and Google services via the Google Play Store. This provides users with an off-the-shelf product, eliminating the need to download third-party data collection software. Juniper Systems has published a blog post that outlines the differences between Cedar and Juniper handhelds.
The Cedar product line that Juniper Systems will now be carrying includes three new handheld devices:
CT7 Rugged Tablet. Featuring a large, 7-inch display, the CT7 tablet is IP67 waterproof and dustproof, and is priced at $899 USD.
CT4 Rugged Handheld. The CT4 handheld is a more compact device than the CT7. Featuring a 4.3-inch display and an IP68 waterproof and dustproof rating, it is priced at $489.
CMP1 Miniphone. The CMP1 Miniphone is rated IP65 (dustproof and resistant to water), and is ideal for swapping out a regular smartphone for outdoor excursions, for kids, or for use as an emergency phone. The CMP1 sells for $124.
Trimble is partnering with unmanned aircraft system (UAS) manufacturer Multirotor service-drone, GmbH. The collaboration will allow Trimble to expand its existing UAS portfolio to provide its customers with additional solutions to choose from based on their aerial imaging project needs.
Multirotor service-drone, based in Germany, is a manufacturer of multi-rotor systems. Trimble will be Multirotor service-drone’s exclusive provider of multi-rotor vehicles for aerial mapping use in surveying, construction, mining, agriculture, oil and gas, and utilities. The combination of Multirotor service-drone’s stable and reliable platforms with Trimble’s industry-leading sensor technology and workflow efficiencies will provide customers with best-in-class solutions for aerial data capture.
Unmanned multi-rotor systems are powerful solutions for visually documenting smaller areas, vertical structures or environments where holding position is important. High-resolution imagery, orthophotos, terrain models and normalized difference vegetation index (NDVI) map deliverables created from multi-rotor data provide valuable information for the survey, engineering and agriculture industries that Trimble serves.
“We are very excited to partner with Multirotor service-drone. At Trimble we’re always looking for ways to meet our customer’s needs and enable them to solve the complex problems they encounter every day,” said Todd Steiner, product marketing director in Trimble’s Geospatial Division. “The collaboration will enable our customers to use a technology rapidly growing in popularity due to its flexibility and productivity.”
Editor’s Note: This month, we introduce a column by David Doyle, one of our two new survey editors. Doyle brings to GPS World more than 40 years of experience as a geodesist and surveyor with the National Geodetic Survey — see his full bio at the end of this article. He will be joined by coeditor Dave Zilkoski, who will contribute the June column.
David Doyle
Since the mid-1980s, thousands of articles have appeared in peer reviewed journals, trade magazines and professional organization publications that describe the phenomenal capabilities of contemporary space-based positioning systems. The majority have been about various uses of the United States Global Positioning System (GPS) and increasingly include the potential for the inclusion of the Russian GLONASS, European Union Galileo and China’s BeiDou collectively referenced as Global Navigation Satellite Systems (GNSS).
Without meaning to understate the process, the ability for almost anyone, anywhere, at any time to determine a three-dimension position accurate to within a few centimeters is well established. I often comment that the systems are generally so easy to use that if you have the IQ of a squirrel you can obtain pretty good quality data. A feat that until recently was achievable only by the small community of geodesists and geodetic surveyors is now a near-trivial process for anybody who can make a modest investment in some form of positioning system device — and it’s getting better, faster, cheaper and more accurate all the time.
Our ability to collect, manage and display monumental amounts of positional data is also enhanced by the advances in Geographic Information Systems (GIS).
I have been privileged to be a part of this revolution since my initiation into the world of geodetic positioning in 1967, courtesy of the Selective Service System and the U.S. Army, and their use of geodetic triangulation combined with emerging artificial satellite systems such as SECOR (Sequential Collation of Range). These introductions to geodesy eventually led me to a position with the National Geodetic Survey and a career that spanned 40+ years.
During that time, we watched as the centuries-old method of triangulation was replaced by GPS, and as the prices of equipment plummeted with the integration of this technology into a multitude of public, private and academic disciplines — everything from geophysical sciences to weather prediction, precision agriculture, improved marine and aeronautical navigation. The list goes on and on and is well known to those who read this magazine.
So where is this going? What does the title of this article mean?
Doyle working on the Washington Monument.
If we accept, which we do, that all these things are true, then why is it that the world of sharing positional information is filled with scenarios that go something like this? “I got a cm and you got a cm, but our centimeters differ by a meter.” What this means is if these systems are so capable, then virtually all positional data integration should be a snap — everything should fit like a bespoke shirt. Unfortunately, that is often just not so.
Take the case of a decree issued by the U.S. Supreme Court in December 2014 delineating the offshore boundary between the United States and the state of California. The boundary is defined as a set of Universal Transverse Mercator (UTM) grid coordinates published to the nearest mm and referenced simultaneously to the North American Datum of 1983 (NAD 83) and the World Geodetic System 1984 (WGS 84), which the decree states are interchangeable. At the mm level, this is not true. In this area, they differ by approximately 1 m.
The decree provided no information on how these positions were derived, how accurate they really are, and who performed the computations — it certainly was not the Supreme Court. Without pointing fingers at the responsible agency, these all-too-common occurrences seems to be rampant among the many users of high-accuracy positional data, both horizontal and vertical. The crime is often the sin of omission.
The failure in many cases is a lack of knowledge on the part of many GNSS users of some of the basic principles of geodesy and geodetic surveying guidelines and providing complete metadata such as:
what geodetic datums and potentially which realization of those datums were referenced?
what are the units of measure?
how accurate are the positions/heights really?
It’s important to note that the number of digits to the right of a decimal point have nothing to do with accuracy. Land surveyors are taught from their first day on the job that they are following in the footsteps of the surveyor that went before them. It is not unusual for surveyors to struggle with incomplete information from previous surveys to be able to make accurate interpretations of what the original or other previous surveyors intended — a lack of complete metadata.
Today, the massive amount of coordinate and height information being generated by thousands of surveyors, engineers and other disciplines are those footsteps — albeit digital. The multitudes of high-quality data being collected around the world is only as good as the associated information about those values.
As we rapidly approach a time when there will be vastly improved GNSS constellations and very likely cm-level positioning available to millions if not billions of people in cheap handheld devices, the issues of professional education and attention to detail are more important than they have ever been. While it would be really nice if everyone who picked up a GNSS receiver had an advanced degree in geodesy, obviously that is not only unrealistic, it’s senseless. What does need to happen is a comment that I’ve made in hundreds of seminars on these topics — those in professions and disciplines where high-accuracy coordinates are important should know enough to qualify for the Junior Geodesist Secret Decoder Ring!
There are efforts in the works at this time that may bring us a step closer to making this a reality. The American Association for Geodetic Surveying (AAGS) is working on a geodetic surveying certification initiative in collaboration with the National Society of Professional Surveyors (NSPS). This effort will be aimed at anyone who is inclined to collect, manage, distribute and/or utilize the increasing amounts of high-quality positional information.
Watch this space for more details next time.
David Doyle joined the National Geodetic Survey in 1972, and held the position of chief geodetic surveyor for 12 years before his retirement in January 2013. He was responsible for the development, technical design and management of plans and programs that enhanced the United States National Spatial Reference System. During his career with NGS, his experiences included all phases of geodetic triangulation, astronomic positioning, leveling, GPS data collection, data analysis, datum transformations, network adjustments, data publication and outreach in the form of seminars, workshops and webinars. His efforts also included extensive activities to direct and coordinate the modernization of national geodetic reference frames in countries in Africa, Central, Caribbean and South America, Eastern Europe and the Pacific.
Doyle is a past president of the American Association for Geodetic Surveying and a Fellow member of the American Congress on Surveying and Mapping. He has served on the U.S. delegation to the International Federation of Surveyors and is an active member of the District of Columbia, Maryland and Virginia professional surveyors associations. Doyle now operates Base 9 Geodetic Consulting Services.
Topcon Positioning Group is expanding the TopNETlive GNSS reference station network into Latin America. In conjunction with hosting partners, new service will be provided in Mexico, Peru, the Dominican Republic, Bolivia, Guatemala, Colombia and Panama.
TopNETlive is designed to deliver high-accuracy GNSS correction data to rovers for surveying, construction, GIS mapping and agricultural applications.
Partners in the Latin America expansion include TTQ of Monterrey, Geomatic Instruments Corporation, Caribbean Positioning System, Mertind, GYFSA and GeoSystem.
“The growth of the network into Latin America through these strong partnerships clearly demonstrates the Topcon commitment to grow TopNETlive and provide quality service to more positioning professionals globally,” said Jonathan Ball, senior manager for the Topcon network business. “Our hosting partners provide outstanding support, training and service to their customers and the addition of the TopNETlive reference stations will allow them to expand their operations by offering real-time network correction data.”
Topcon dealers will host TopNETlive throughout the various regions, which include: TTQ of Monterrey for Mexico, Geomatic Instruments Corporation in the Peruvian market, Caribbean Positioning System in the Dominican Republic area, Mertind Ltda in Bolivia, GYFSA in Guatemala, and Columbia-based GeoSystem will host the network throughout Colombia and Panama.
CHC has launched the LT500 series of handheld GPS receivers. The LT500 series LT500N /LT500T/LT500H covers three accuracy ranges from sub-meter to centimeter accuracy and is a cost-effective full GNSS positioning solution for survey, construction and GIS professionals.
Powered by the Windows Embedded Handheld 6.5 operating system, the LT500 is accurate, rugged and versatile, CHC said. User productivity is enhanced with the built-in gyroscope, an innovative laser plummet for positioning the accurate handheld receiver over a point, an E-compass for showing the direction and G-sensors for leveling.
The LT500 series is competitively priced and comes with several bundled software programs, including SurvCE, DigiTerra, MapCloud and other third-party software.
“CHC’s LT500 series is our brand-new GNSS handheld, which has amazing features and specifications. It meets more customers’ needs with more options and affordable prices,” said George Zhao, CEO of CHC. “The introduction of the LT500 demonstrates CHC’s commitment to provide the GIS community with a full spectrum of rugged, cost-effective professional GPS handhelds.”
The CHC LT500.
The LT500 series features these specifications:
1-GHz high-speed CPU with 512-MB RAM and 16-GB flash memory built-in
“We have found the FOIF GNSS receivers are very easy to use, and the epoch readout on screen is very reassuring that the data is being stored, and easily confirms that the correct amount has been stored. The data is easily downloaded from the card and converted to Rinex format with FOIF RnxTransform. The data was post processed by a third party.”
