Trouble with incorrect EPSG

Hey all

I am new to the WebODM software and am currently trying to figure it out. I have been experiencing issues with my EPSG code. I have looked into the Proj.4 string for my area and that also throws my GCPs way out.

I am using NAD83 / Massachusetts Mainland (ftUS) + NAVD88 height (ftUS) EPSG:8748

here is the .txt file for my GCPS;
5025,3089260.28525,742594.40782,89.06186,AERIAL MAG
5030,3087753.37194,742674.31645,74.83826,AERIAL TARGET
5031,3087982.31042,742653.42608,73.13136,AERIAL TARGET
5032,3088175.85032,742649.13247,74.62369,AERIAL TARGET
5033,3088560.31547,742638.95712,90.42215,AERIAL TARGET
5034,3088905.93714,742627.68343,90.57252,AERIAL TARGET
5056,3087585.69103,742675.76791,80.47572,AERIAL TARGET

Not sure if the format is correct, but iv also tried Lat and Lon format for my points as well.

this is the location of my GCPs after using the format above with the Proj.4 string from
+proj=lcc +lat_0=41 +lon_0=-71.5 +lat_1=42.6833333333333 +lat_2=41.7166666666667 +x_0=200000.0001016 +y_0=750000 +datum=NAD83 +units=us-ft +vunits=us-ft +no_defs +type=crs

Any help would be greatly Appreciated.


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It seems I finally found a possible solution to my problem. I switched to the GCP editor Pro and changed my GCPs from horizontal (Ft) to horizontal (M) and then kept my elevations in US feet. I also used the EPSG:26986.

seems to be working for now as it tracks my GCPs to their correct locations. will update here later when I finish

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You might have your northing (y) and easting (x) swapped.

The POSM GCPi is loaded by default on WebODM. An example is available at the WebODM Demo. To use this with known ground control XYZ values, one would do the following:

Create a GCP list that only includes gcp name (this is the label that will be seen in the GCP interface), x, y, and z, with a header with a proj4 string of your GCPs (make sure they are in a planar coordinate system, such as UTM.


Good luck