GNSS coordinates as survey evidence — friend or foe?

September 7, 2016  - By

In my last column in July, I shared the situation with U.S. federal lands in Alaska being surveyed with GNSS and subdivided by coordinates, instead of subdivided by traditional methods of setting monuments.

The topic drew a varied range of responses and opinions. While some felt the article was on point with setting bad precedents, others added that it was time for technology to take over and not put so much priority on physical monuments.

I do believe there is room for everyone at the table and would like to use this article as a follow up to more conversation. Let’s start with a comparison of monuments versus theoretical/published positions for parcel corners and land ownership.

On the technical side

Space – the final frontier. Everything these days has a spatial address and/or relationship. Thanks to the U.S. Department of Defense (and taxpayer’s money), the global positioning system was created. While originally designed for military use, the civilian application has opened up a new world of spatial technology.

From Google Earth and municipal GIS to vehicular navigation and Pokemon Go, spatial data has expanded and tracked almost everything in our lives. Where’s the package from Amazon Prime? Let me check the app on my phone and it will show me where my wife’s shipment of make-up is via RFID chips on the box. Where are my buddies tonight? The “Find Friends” app tells me in seconds. All things spatial and right at your fingertips.

So that brings us to surveying and how technology has influenced its historical methods. Coordinates aren’t new; the introduction to State Plane Coordinate Systems was developed and publicized by the U.S. Coastal & Geodetic Survey almost 100 years ago.

First-order horizontal monument, U.S. Coast and Geodetic Survey, 1931.

First-order horizontal monument, U.S. Coast and Geodetic Survey, 1931.

This allowed for the creation of large networks to begin the framework of today’s GIS but not without its flaws. Instruments used for these measurements were very accurate but human error always played into the final computation. Positions established by observing Polaris and/or sun shots were somewhat accurate but often were too complicated for everyday surveying projects. For decades, the only projects in which state plane coordinates were utilized took place during larger state and federally funded surveys. Because of these limitations, use of state plane coordinates and networks didn’t have many followers.

Forward a few decades and the invent of the electronic distance meter (EDM). Now there was technology available (albeit expensive) to measure large distances but it brought its own issues. Up to this point, surveyors didn’t need to worry about the earth’s curvature and atmospheric corrections but the EDM changed that.

With the Eisenhower interstate highway system, more federally funded surveys were performed and surveyors were embracing state plane coordinates more than ever. Primitive GIS systems were starting to form but state and federal cartographers were the stewards of this data. Another big step was needed and the late 1970s/early 1980s didn’t disappoint.

As mentioned earlier, the Department of Defense began implementation of the GPS network by sending a new breed of timing satellites into orbit beginning in the late 1970s. When decisions were made to allow civilians to receive GPS signals for positional use, a new era opened up for surveying. But just like route surveys, EDM’s and control networks, only large projects could sustain the funds necessary to utilize early GPS receivers. Over time, GPS equipment, like computers and software, became more advanced, user friendly and cost effective. Cost of entry to GPS technology became more affordable to most surveyors and expanded the capability of the profession to embrace state plane coordinates. For the surveyor community, the thought of an entire profession working within one large coordinate system was almost nirvana. It could help solve many of our ambiguity issues in comparing similar survey data. With today’s options of GPS networks, this dream is much closer to reality.

In one of my previous articles, I shared my belief that the GNSS RTK network has been the single greatest improvement to the profession of surveying. The hard work put in by the National Geodetic Survey team in establishing and maintaining the National Spatial Reference System (NSRS) provides a thorough network that is confidently used nationwide and beyond. Additional Continuous Positional Reference Stations (CORS) are being installed nationwide and providing more surveyors with the network capability to perpetuate state plane coordinate systems literally anywhere. I, for one, like the idea of being able to share data with some certainty that most of my fellow surveyors are on the same datum.

While the autonomous car may be several years out, the surveying community now has the tools to put all surveys and property corners on the same coordinate datum. Or do we?

Every man’s house is his castle

As a surveyor, the measurement of land has been the primary focus of my career and the biggest part of it has been the search and recovery of monuments. Other than family, a person’s home and/or real estate is their most prized and valued possession. Knowing where the limits of their ownership is very important; this is where the surveyor comes in and provides that knowledge. Establishing boundary limits with monuments is a critical role the surveyor performs; how do they get there?

Monuments mean different things to everybody. Ask the person on the street what they define as a monument and they will most likely name the Washington Monument, Mt. Rushmore or another historical statue or building. History has a way with things and places being “monumental”. Here is Webster’s definition:

Full definition of monument

  1. (obsolete): a burial vault: see sepulchre
  2. : a written legal document or record: see treatise
  3. a (1): a lasting evidence, reminder, or example of someone or something notable or great (2): a distinguished person
    b: a memorial stone or a building erected in remembrance of a person or event
  4. (archaic): an identifying mark: evidence; also: portent, sign
  5. (obsolete): a carved statue: see effigy
  6. a boundary or position marker (as a stone)
  7. see: national monument
  8. a written tribute

Depending on what part of the world you are in, monuments of different sizes, shapes and materials are used for marking boundaries. Surveyors working westward after 1800 were setting hedge posts, large stones with pointed tops and stone mounds. It wasn’t until the Industrial Revolution with mass production of steel mills were iron bars and pipes used for setting section and property corners. The invention of the metal detector further increased the use of ferrous materials for corners and monuments by increasing the ability to recover the points at a later date. Over time, additional materials were introduced; brass tablets, steel reinforced rods, and stainless steel masonry nails being the most common.

 Typical property corner: 5/8-inch steel rod with ID cap (Illinois).


Typical property corner: 5/8-inch steel rod with ID cap (Illinois).

No matter what the material, points are set at appropriate locations to physically mark the intended corner. It is also the duty of the surveyor to inform the property owner of the results of the survey in order for parties being affected by the placed points to know where their boundaries are located.

Trouble in paradise

Surveyors have been measuring for centuries using a plethora of instruments and methods; how could introducing GNSS coordinates to everyday projects create issues? It once again comes down to training, understanding of the equipment and technology and how to relate vintage survey data to newfangled data collection and measurement. Here are a few of the potential problem areas:

  1. Working in Ground or Grid Coordinates? What geoid model are you working with? You mean there’s a difference? It’s amazing to me the amount of surveyors that don’t know that there truly is a difference. If you are using GNSS/GPS and don’t know the difference, put the receiver down now and pull out your total station. Same goes for the geoid model; if you don’t know the difference between orthometric heights and ellipsoid heights, look it up and learn ASAP. Your data will thank you.
  2. Relating survey data based upon conventional plane geometry versus GNSS data based upon spherical geometry. Depending on the age of the survey data, it could have been collected by several different method, (chaining, EDM, triangulation,etc.) and will vary from GNSS data collection. Just because your data collector coordinates reads to ten decimal places doesn’t make it more accurate that old measurements. Get to know what is acceptable variations in measurements from old work and when real trouble is lurking, not just the occasional tenth or two.
  3. Varying correction signals from RTN network providers. While any network being used for GNSS RTK data collection worth its salt is being monitored for anomolies, things happen and signals can get compromised. Check your data, then check it again. Just because the data collector says the horizontal and vertical precisions are within tolerances, they can and will lie. Check periodically to make sure everything is in good working order. Watch your satellite counts and constellations as well for good geometry. Just like any other measuring technique, proper procedures must be followed.

These are just the highlights of potential issues and not intended to be a comprehensive list.

Can’t we all just get along?

On one side of the fence is Old Joe Surveyor with his trusty metal detector, shovel, total station and sidekick for a prism holder. He’s the one finding irons and shooting fences, looking for signs of occupation because “that’s the way he was taught; follow in the footsteps of the original surveyor.” He doesn’t like technology and would prefer if those who have it would just stay away and leave him be. For him, 2 + 2 = 4, but it might need to be prorated down to 3.95 depending on the monuments.

On the other side of the fence is Kyle the New Surveyor/Geomatics Professional. He’s talked his boss into the latest toys; GNSS on an RTN network, robotic total station with scanning capability, and working on the getting the UAV flying soon with his Part 107 certification. He sees the world as one big GIS database and everything is spatial. Utilities, property corners, and improvements have coordinates with physical addresses just waiting to be collected and stored in the “cloud”. Everything is mathematics, equations and algorithms; numbers don’t lie. For Kyle, 2 + 2 = 4 because the professor said so and completed the proof during lab time.

While I know these two gentlemen are the extreme opposites of most surveyors, they epitimize a great deal of what is seen in every day business. When these two cross paths, there will always be differences until we can work out common ground for both. For instance, my last article included the “Rule of Construction” for analyzing survey data:

Priority of Evidence Rules

  1. Possessory Evidence
  2. Seniority of Title
  3. Documentary Evidence

a. Call for a survey

b. Call for monuments

i. Natural

ii. Artificial

iii. Record

c. Distance (or Direction)

d. Direction (or Distance)

e. Area

f. Coordinates

Kyle loves his coordinates. See where coordinates fall? This is because case law has established the higher weight of survey information. Distances and bearing are above them simply based upon how things have been establish and marked for many generations. Of course, Joe sticks to the monuments. Notice on top of the list is “Possessory Evidence”; fancy words for monuments or other features depicting occupation and/or possession. These are tangible, real items that are observed, locations recorded and relied upon by both the land owner and the surveyor to define boundary lines.

This goes back to the section above about a “man and his castle” and he wants to know where his kingdom lies. It may be iron rods, fences, shoreline, creek, etc., but he can see it and know what he owns. Because these landowners are the clients of the surveyor, we provide them what they want; tangible boundary limits physically defined.

But monuments can be a divisive as well. Here is another reason I don’t want to see coordinates take a higher priority:

monuments-divisive

As a young surveyor, the term I was taught was “pin farm” and they grow like weeds. Most surveyors feel their corner will be superior to the others and therefore set another rod right beside the others. Jeff Lucas, surveyor and attorney from Alabama, wrote an entire book on “The Pincushion Effect” because of situations like this. When several different surveyors using different GNSS on the same theoretical coordinate system stake a corner based upon varying evidence, this is what we get.

Also, GNSS might not be involved at all and is simply based upon conventional survey data collection. Or some mix of all of the above. Either way, I count five (5) iron pins and the fence corner; which one fits the data best? Better yet, which one is right?

The big difference with these examples versus last article’s concern about surveying tens of thousands of acres in Alaska that no one will ever inhabit is simple; it is setting a bad precedent. The surveys in Alaska are to be performed by the BLM and follow their specific guidelines for original surveys, so they are unique in that respect.

However, by not setting corners per their own standards and utilizing a coordinate-based plat for subdividing townships will send an unintended message to surveyors throughout the states. That message will be that setting corners for government lines will no longer be necessary and simply file a plat with coordinates at your local recorder’s office. If you don’t think it will happen, just check out the multitude of surveyors who use the BLM manual for recreating sections by original surveyor instructions instead of retracement methods. Bottom line is they simply don’t know better.

As I’ve stated in past columns, I enjoy technology almost as much as I enjoy surveying and hope the innovations continue. I want to continue to push the limits of what we can do with the equipment, software and data but also not forget who we are working for. The clients are the ones who rely on our expertise to show them what they own and how they can work with their property. Spatial data is here to stay and look forward to utilizing it more in all aspects of surveying and engineering. However, existing laws and court cases are going to have to catch up to the technology before we can start placing higher priorities on coordinates and digital data. I do utilize it as much as the next surveyor but try to use it wisely. After all, just like any other professional, aren’t we “practicing” surveyors?

This article is tagged with , , and posted in Opinions, Survey

About the Author:

Tim Burch, GPS World’s co-contributing editor for survey, is director of Surveying at SPACECO Inc. in Rosemont, Illinois. He has been working as a professional land surveyor since 1985, and is the secretary, Board of Directors, National Society of Professional Surveyors.

5 Comments on "GNSS coordinates as survey evidence — friend or foe?"

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  1. Robert J Farmer AK-PLS says:

    I am a registered surveyor in Alaska and I think that monuments need to be set because as stated that is what the layman depends upon for locating his boundaries. Also anyone who has done much GPS surveying in the state can tell you we do not have a CORS system at this time that covers the entire state. Many times have I submitted 4 hour statics to OPUS to find out that I am outside of the triangulation network of the local cors stations.
    I disagree with your statement about 10s of thousands of acres that will never be inhabited. I am sure that was the same sentiment that our fore fathers had about the development of the “west” back in the early colony days and look what we have now.
    Some day Alaska will have roads that access large portions of now inaccessible lands. When this happens so will development. I can remember when we first moved to Alaska in the mid 60’s my Dad saying that nothing would be developed in the Mat-Su valley beyond what they had at the time and look at us today several 100,000 people living in one of the fastest developing areas in the state.

  2. Timothy Burch says:

    Robert –

    Thanks for your comments, especially with your direct experience with GPS as a fellow surveyor. I meant no disrespect in stating the surveys in Alaska would be for uninhabited lands; I would have to think that large parcels will be sold for ranches or energy exploration before they would become the “next boomtown”. Bottom line is that when the surveys are completed, careful thought must be used if it is chosen to go down the DPPS route.

    Tim

  3. Edward S. Ruchin, P.L.S. says:

    I recall going to a seminar in Rhode Island presented by a professor from the University of Maine who obtained his PHD based upon his thesis that ALL boundary corners should be based upon a Lat-Long coordinate system derived from GPS/GNSS observations…

    My opinion based upon 40+ years of surveying licensed in three states:

    Although Land Surveyors are supposed to be experts in measurement when it comes to GPS/GNSS procedures I have seen wide gaps in CORRECT analysis of the data.

    I also recognize the issue that the land owner will review their plot plan see a LAT-LONG as a corner… plug it into their I Phone and walk over to the I Phone’s LAT-LONG which could be FEET from the intended coordinate; or plug in their coordinates in Google Earth and find they are not on the fence line they put in.

    I have not even taken in to account the availability to obtain LAT-LONG in heavily treed or urban scenerios. Try taking GPS/GNSS readings in canyons of Manhatten…or the lightly foliated woods of Muir Woods in California…

  4. Dan Kalstrom says:

    Tim,

    I’ve been using the Ohio SPCS around the Akron, Ohio area since the late 60’s using terrestrial and now GNSS methods. When we first started the system was based on NAD 27 and since has been re-computed to NAD 83. As everyone knows NAD 83 has been readjusted a number of times over the years. The problem as I see it, is that if you base corners on coordinates observed today, how can you safely assume that a conversion to future reference systems will put you closer than a known monument position.

  5. Tim,
    I hope we, at least in countries that acknowledge private property, never forget the purpose of locating property corners.

    As surveyors, our actions are in the stead of the property owner. Many activities he may undertake or avoid will depend upon the understood location of his boundary. We may not assume he is technically astute – that’s what he hired us for.

    Governments are hogs for data – especially data provided by someone else. Hence, “any plat or … must include utilities … With coordinates plainly evident, preferably provided on digital media.” This service ONLY the database managers and occasionally a legitimate planner.

    Using coordinates AS monuments is folly. Is there anyone versed in geography/geology/surveying/TV programs who hasn’t heard of plate tectonics? The land moves while the coordinates stay put! Over time, one’s legal description will no longer be coincident with his fence. His set-backs will be wrong.

    A physical monument will move with the ground. Over time its coordinates will change, but it will still “be in the same place” as understood by the common man.

    No doubt about it. Geodetic (state plane) coordinates are fantastic for location. Just not for monumenting. They should be considered like super bearing trees, telling one where to look for the corner.

    JAC