NAD83 stake out

GPS/GNSS Development Boards
1

Hi, I have LiDAR data and imagery from an RTK corrected drone based on NAD83 (2276). I’m using it to plan boundaries for a pond and some buildings, then I’d like to stake out the points I overlay back on the actual ground.

When I use various online tools (eg mygeodata.cloud) to convert to WGS84, some of our known Ground Control Points and stationary objects are ~4 feet away from the point shown in SW Maps (iOS) with an RTK Fix on the Facet L-band. Is there a way to correct this in bulk on a set of points?

Also, it seems like SW maps doesn’t have a “staking mode”. So far, all I can do is zoom in, get close graphically, and then repeatedly tap the point & cancel to get snapshots of dx/dy until close enough. Is there a better way or better app to use for this purpose? Thanks!

2

Which axes are showing the discrepancy? If vertical only, it is likely needing the antenna ARP offset entered https://docs.sparkfun.com/SparkFun_RTK_ … e/#sw-maps (that link also has the list of supported software)

We have a guide for converting NAD83 and using that to verify accuracy https://docs.sparkfun.com/SparkFun_RTK_ … 3-to-today that might shed some light

3

Thanks, for this work I’m only concerned with x/y. If I put the Facet on top of a known ground point in the lidar survey, it registers approximately 3.8ft deviation on x and -1.8ft on y.

4

Such values are typical of plate motion troubles. “The North American plate is moving to the west-southwest at about 2.3 cm (~1 inch) per year”. If you multiply it by (now-1983.0), you would get 34 cm South and 89 cm West. What about the CORS station used? Is it configured in NAD83 or ITRF@now or something else?

5

Thanks. After looking at some of the points individually, it does look like HTDP adjustment is the culprit. I guess mygeodata/etc just convert the coordinates without adjustment.

For my data to work, I had to convert my x/y to lat/lon via, e.g., https://www.earthpoint.us/stateplane.aspx and then input into the HTDP tool as lat/lon.

Also, I found this github Fortran source for the HTDP tool, I was hoping to be able to automate the process since there are quite a few points and this should allow me to pipe them in vs manually inputting everything. https://github.com/noaa-ngs/HTDP

I will dig up an Android phone to try to use the other apps and see if they have better staking UI. Thanks for the pointers y’all!

6

Eric_S:
Such values are typical of plate motion troubles. “The North American plate is moving to the west-southwest at about 2.3 cm (~1 inch) per year”. If you multiply it by (now-1983.0), you would get 34 cm South and 89 cm West. What about the CORS station used? Is it configured in NAD83 or ITRF@now or something else?

Yes, thanks, it appears that is the issue as the conversion tool I was using does not make the HTDP adjustment. CORS station is PointPerfect via Inmarsat on the RTK Facet L-band.