Hays, GCPsToGeoTransform() is not used directly by gdalwarp (although it should likely be equivalent to running -order 1 polynomial), but by other code (OZI .map exporting, .tab exporting)
You rather want to use the gdal.Transformer() API which is tested in https://github.com/OSGeo/gdal/blob/master/autotest/gcore/transformer.py Even > Hello all, > I want to get the error for each GCP before warping so I can calculate the > RMSE before georeferencing. With a list of GCPs, is it possible to get the > eventual map location of each pixel coordinate to calculate the > transformation error for each GCP? I have tried to use GCPsToGeoTransform > but that gave me a map location that was further from the intended chosen > GCP coordinate than the actual post- georeferencing pixel location. > > Here is my GCPsToGeoTransform code: > ##CODE_START > > from osgeo import gdal > #list of GCPs > gcpjson={'0': {'row': 5305.626973704321, 'col': 1158.432032601927, 'lat': > -107.18221364936802, 'lon': 35.08107313264506}, '1': {'row': > 778.3230540174817, 'col': 2317.0737231100225, 'lat': -107.17634116783263, > 'lon': 35.09958594602314}, '2': {'row': 3950.8777704175645, 'col': > 4880.465723118029, 'lat': -107.163460244414, 'lon': 35.08679518563491}, > '3': {'row': 7609.882307742781, 'col': 4407.027704042081, 'lat': > -107.16570574683065, 'lon': 35.07164256912238}, '4': {'row': > 1822.0904204049455, 'col': 6486.900377637105, 'lat': -107.15529960157271, > 'lon': 35.096105471961536}, '5': {'row': 6291.396402113635, 'col': > 7216.1033738731185, 'lat': -107.15180240538085, 'lon': 35.077317337370516}} > > #New list to put in gdal.GCP objects into > gcpList=[] > #Load GCP objects into gcpList > for gcp in gcpjson: > gcpList.append(gdal.GCP(gcpjson[gcp]['lat'],gcpjson[gcp]['lon'],0,gcpjson[gc > p]['col'],gcpjson[gcp]['row'])) > > #create GeoTranform from gcp list > GT = gdal.GCPsToGeoTransform(tuple(gcpList)) > > #Get pixel location from first GCP as a test. > col=gcpjson['0']['col'] > row=gcpjson['0']['row'] > xp = GT[0] + col*GT[1] + row*GT[2] > yp = GT[3] + col*GT[4] + row*GT[5] > print("POINT ("+str(xp)+" "+str(yp)+" 0)") > > ##CODE_END > > This prints out the WKT 'POINT (-107.18216298 35.0808978834 0)' which is > kinda close to -107.18221364936802, 35.08107313264506 but looking at my > post warped image the chosen pixel is right on top of the intended > coordinate so I am clearly doing something (or a lot) wrong. > > > > Any help would be great. > Thanks, > -Hays -- Spatialys - Geospatial professional services http://www.spatialys.com
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