You can see the QGIS implementation in https://github.com/qgis/QGIS/blob/7d1ca8161882cf03b9a384b6e294fc9ce5f45ed8/src/app/georeferencer/qgsgeorefmainwindow.cpp#L1451-L1495
It breaks down to error = std::sqrt( ( sumVxSquare + sumVySquare ) / ( nPointsEnabled - mGeorefTransform.getMinimumGCPCount() ) ); where: sumVxSquare is the sum of the squares of enabled points x residuals, sumVySquare is the sum of the squares of enabled points y residuals, nPointsEnabled is the number of enabled gcps, mGeorefTransform.getMinimumGCPCount() is 2 for linear and helmert, 3 for polynomial_1, 6 for polynomial_2, 10 for polynomial_3, 4 for projective and 1 for TPS -- Sent from: http://osgeo-org.1560.x6.nabble.com/QGIS-User-f4125267.html _______________________________________________ Qgis-user mailing list [email protected] List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
