My goal is to log RTK Fix GGA coordinates from my Sparkfun Postcard/Portability Shield and to be able to find those points on Google Maps. However, when I enter the GGA positions that I get from the Postcard into Google Maps they are displayed more than a meter away from where I was.
For my base, I am using the IaRTN network. I realize that the base units are tied to IGS08@2018.8123. But, even using pyproj to transform the GGA positions from IGS08@2018.8123 to WGS84, they are still way off.
Does anyone have any hints to help me get coordinates that display in the correct spots in Google Maps?
That’s unfortunate. As an amateur historian, I wanted as easy way to document, to a high degree of accuracy, the location of found artifacts and to give to those who follow me a common tool (such as Google Maps) a way to visualize where the artifacts were found. I will probably continue to develop Sparkfun Postcard solution with enough documentation to allow future generations to figure out “this was here, and that was found over there”.
AFAIK, NAD83(2011) is EPSG:6318 and Iowa for projected maps uses EPSG:6343 , both can be converted in EPSG:4326 used in google earth (note that the latest WGS 84 is G2296 aka EPSG:10606), but google maps use the projected spatial reference system EPSG:3857 (Pseudo Mercator) that is a projected coordinate systems FROM the surface of an ellipsoid towards a flat surface, while EPSG:4326 uses a coordinate system ON the surface of a reference ellipsoid,further all this is confused by the fact that even though the g. map is in EPSG:3857 like UTM, the coordinates actually used are commonly expressed in latitude/longitude (as if it were in EPSG:4326, on a plane).Obviously g. maps has transformation algorithms consistent with latitude/longitude but the g. map itself, as Ryan says, is not aerophotogrammetric (look at the shadow of buildings projected on the side) and the position will never be accurate. IMHO there are too many transformations,epocs and datums to scale beginning the consideration that the geocentric NAD83(2011) lies by a precedent plate-fixed N.A. and it is always deferred from WGS84 so let’s remember that it doesn’t count where but when.
The Sparkfun RTK lineup lets you do that
If you publish the metadata along with the coordinates, those positions are real and valuable for eternity. As you know, the minimum info is the specification of the correction source used during RTK data collection.
For your Iowa Network :
Pt #, N.xxxxxxxx, E.xxxxxxxxx, HAE, Description
Pt #, N.xxxxxxxx, E.xxxxxxxxx, HAE, Description
all RTK fixed positions referenced to: NAD83(2011) Epoch 2010.00 (IGS08@2018.8123) via IaRTN
That can be used 100 years from now to transform into whatever System they use in the future. As Marco points out - we must ensure to leave no ambiguity for future users.
I think it’s wise to publish the GGA sentences (modified to include Point #, in an appendix) so users can see the metadata for individual positions such as UTC Time, Fix Quality, # Satellites, HDOP, Correction Age, Station ID, etc. You have the data anyway.
You could also consider producing a georectified orthomosaic of a artifact site to document the existing conditions at the time of discovery or recovery. It’s been fairly easy for the past decade, even with consumer-grade UAV’s. Now we have opensource options to Pix4D such as OpenDroneMap, etc.
Since you have RTK figured out, you are already well into the learning curve of creating custom aerial imagery with an accurate projection
Users can still use Google Maps to view your custom tiles at the various sites (as overlays).
@LenS, since the Iowa Real Time Network is organized a little differently that other states, I looked around a bit.
You will want to use the RTCM 3.2 MSM4 IMAX MountPoint.
You will also want to ensure the PostCard positions are indeed RTK Fixed quality before comparing to aerial imagery. There’s a good chance you are already doing both, but it never hurts to check
Wow! Thanks! I had not noticed the Note 3 about L5. That may make a difference. I hope to be doing some more testing today.
And thanks to everyone for all of the responses. My brain hurts from all the new knowledge I’m trying to stuff into it!
Another thing that I am investigating is that the GIS department for my county (Linn) provides free access to high quality orthoimagery. However, now I need to figure out how to handle .sid format image files. <sigh! Watch out brain!>
Just another THANK YOU to you all for getting my Geodesy education started. I have found the excellent YouTube videos from the Geospatial Users Group presented by Dave Doyle. Even though these vids are 8 years old, they are still applicable. Mr. Doyle is such a good presenter that learning the basics was… actually fun!
So far, I’ve got both the Sparkfun Postcard and the Waveshare LC29H HAT GPS RTK receivers working and I’m well on my way to being able to use them for my history projects.
