Does anyone have an iOS app for collecting GCPs?

General Discussion
1

I have a trimble SPS585 that bluetooth connects to my iPhone/ipad and takes over location services, does anyone have an iOS app to collect GCPs?

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2

Are you going to need localization?

3

Not exactly sure what this is but I don’t think so, looking to make elevation maps for agriculture, possibly for tiling.

4

If you are looking for elevation maps based on real world ground elevation then you will need localization. GNSS receiver use an ellipsoid for elevation. You can Google “ellipsoid vs geoid” to understand the calculated difference. Ground elevations are yet another thing. Basically ellipsoid is a mathematical representation of the earth. Geoid is a gravity calculation that simulate the terrain better. Ground is the actual elevation as would be leveled in by a surveyor and related to elevation benchmarks that surveyors, infrastructure and construction use.

Localization takes the monumentation that is on the ground (benchmarks, property pins) which is always slightly (or very) different from what you would see on a plat or engineered plan. Localization links a WGS84 coordinate (lat and lon) to the actual location of the “known” point and after at least 3 points have been located the program will prorate all error in X, Y and Z to make your survey as accurate as is possible in relation to the error of the monumentation.

Bottom line is if you want the actual ground (sea level) elevation then you need to do a localization. If you only need relative elevations to do a drainage study and don’t care where it is actually vertically at in relation to the MSL and real ground elevations then localization is not needed. The same thing for tiling. Relative elevations are fine, but they may not be in actual measurement relation to what is on the ground. GNSS uses metric ellipsoid so what the relative delta is between two points may be different than what it actually is on the ground.

This is a big problem in drone mapping. Allot of people are grabbing a drone and try to make maps without knowing anything about surveying and GNSS. Making simple, not absolutely or relatively accurate maps is fine, but when you try to start getting the accuracy and relate to the rest of the world there are methods and protocols that need to be followed. I would suggest getting on YouTube and look for instructional videos on:

Land Surveying
How GNSS GPS Works
Localizations
Ground control points complete guide (101)

Always happy to help on here. PM me any time.