Daily Archives: February 2, 2023

Let’s raise the level of informed Geodesy in the UAV, GIS … worlds.

We (iGage) sell a lot of GNSS receivers to a variety of markets: survey, engineering, GIS, UAV, agriculture, machine-control, marine, and other interesting uses.

Because we support and service what we sell, I have a lot of interactions with customers who are experiencing failures or difficulties. In talking to them I repeatedly encounter the same reoccurring issues.

Yesterday I talked with a new UAV operator who was bragging about how accurate their results are. The claim is 2 x 3 mm (2 mm horizontal, 3 mm vertical). But, this operator was having some issues with the site control that they set using a static receiver purchased from us.

After talking for a while, I realized that I can’t take this anymore.

Question 1: Do I really have to be polite or can I just tell them to fo and hang up? (I guess we know the answer to this question: I have to be polite.)

Question 2: how can a UAV operator claim to achieve 2 x 3 mm accuracy if they:

  • Don’t know the difference between iFeet (international) and USFeet (Unites States Survey Foot).
  • Have no idea what Grid and Ground distances are.
  • Don’t know what the difference between ‘plate fixed’ and ‘current epoch’ is.
  • Don’t understand the difference between a reference frame and a projection. So they can’t tell You if their data is NAD83xxxx, IGSxx or ITRFxxxx because they don’t understand the difference. Honestly, most claim their data is WGS84 (whatever that might be) when it is actually NAD83 framed. And, I have to ask, does anyone in the USA other than airport operators and the Army want WGS84 framed data? And if someone wants current epoch data, won’t they know and ask for a specific realization? My experience is that anyone who asks for ‘WGS84’ really wants ‘NAD83_xxxx xxxx.xxx’: but they don’t understand that WGS84 is not NAD83, nor do they understand how foolish they appear. If someone really wants current epoch ITRF_xxxx they will ask for it by name, not by some generic, non-specific label like ‘WGS84’.
  • Throw around the term WGS84 but can’t tell you if it is IGS08, ITRF2014 or one of the many other realizations. They scream “I want WGS84!” thinking they are brilliant little UAV geodesists.
  • Have no clue how they might actually convert a current/specific epoch ITRF/IGS coordinate to NAD83xxxx.
  • Can not perform mission planning, in the correct time zone, to determine a best time-of-day for a 15-minute OPUS-RS occupation.
  • Think they can do a 15-minute OPUS-RS occupation and get a 2-mm vertical solution, anywhere in the USA at any time, under any canopy.
  • Don’t have access to NGS OPUS-Projects, so they can not get a more accurate orthometric position on their own: [ see opus-static-a-deep-dive-into-orthometric-height-estimated-errors ]
  • Don’t understand that a relatively accurate ellipsoid height returned by OPUS may not be an equally accurate orthometric height.
  • Don’t understand that selecting different CORS sites to process against will result in different results.
  • Can’t wait for precise ephemeris. Can’t wait for CORS stations that post daily to become available, forcing their 15-minute OPUS-RS solutions to use excessively long baselines to distant CORS.
  • Do not understand the difference between ‘ellipsoid’ and ‘orthometric’ heights, have no idea what a GEOID is, do not understand that the GEOID is NOT a function, but a lookup table. Do not understand that the GEOID is a representation of gravity. Are unaware that water does not necessarily flow downhill in ellipsoid space. Have never transferred an orthometric elevation between two points nor do they have any equipment that would be suitable for this purpose.
  • Have no idea if their GNSS receiver NMEA strings are ellipsoid or orthometric and if orthometric, which GEOID was used to generate them? How to convert an inaccurate NMEA orthometric height to an accurate orthometric height.
  • Have no clue that solid earth tides exist. Have no clue that tidal loading is significant near coastal regions.
  • Don’t understand that the earth is not flat and the curvature is significant over very short distances.
  • Claim to have single digit mm accuracy, but set control and checkpoints with GPS. Sub-centimeter GPS is really tricky. If I was going to claim 1-mm accuracy, I would probably set control with my 1″ robotic total station, not GNSS, right? And all my equipment would be in absolutely top notch condition, cleaned, adjusted and calibrated. But they:
    • Have never adjusted the bubble on their rover pole. (In fact, they have no idea that the bubble is adjustable.)
    • Have not checked the rover pole for runout (is the rod straight?) Spoiler: the rods are NEVER straight. Even new, in the box from the factory the poles have excessive runout.
    • Have never cleaned or adjusted a tripod. (The metal feet literally are loose and rock, the leg hinges are loose, the quick locks on the legs don’t hold. The tripod looks like it has been run in a cement mixer barrel with bags of gravel. The slides are packed with sand and jump when you extend them.)
    • Have never checked the alignment of their tribrach, nor do they have access to an adjusting cylinder. Or a clue how one might check or adjust a tribrach.
    • Don’t own a total station and have never done a field calibration.
    • Use GNSS equipment with non-calibrated antennas. (So the antenna that they are using does not have an NGS relative or IGS absolute calibration.)

I am not going to offer answers to any of these questions today.

My impression is the kids I am talking to have convinced themselves that they are the smartest guys in every room that they walk into. An old guy like me could never help them. But if you read through the items above and don’t definitively understand their points; trust me: you probably should not be offering UAV/GIS services for hire.

Also, at this point I feel the need to disclose that I am not a surveyor, I am not a geodesist, I am no longer even an engineer. I am just a guy who sells survey equipment. And I personally certainly have a lot to learn about geodesy, measurements, coordinates, frames, processing static data, doing adjustments and even more stuff that I don’t even know about. If you read the previous few months of my arcane blog entries, this will be clear.

Oh, one more thing, if you are a UAV operator and you talked to me yesterday, this rant is NOT about you. It is totally about someone else. Totally.

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