GCP Management > Residual and RMS Errors

Residual and RMS Error

When there are more than 4 GCPs in GCP Manager of SuperGIS DataRectifier, the program will automatically calculate the current residual and RMS errors, which enable you to check whether the GCP setting is appropriate or not. If the GCP setting causes the value of residual or RMS errors to be too high, you can adjust the details in GCP Manager in order to get a better rectification result. Residual and RMS errors can be seen as the essential statistics for us to decide whether to modify the rectification setting. Also, the statistics can prove the accuracy of the rectification.

Residual

Residual is a standard deviation calculated by the estimate value and the actual value. Here, it means the standard deviation of the estimated GCP location and the actual GCP location. Any two corresponding GCPs will generate a set of residual.

RMS Error

RMS error is calculated by the distance between each GCP on source layer and reference layer to get a more accurate rectification. After the GCPs are added, the RMS error will be calculated with the unit as grid. RMS error value might be influenced by GCP location, quality of source layer, and other related factors, so it is suggested that the value should be less than 1.

In general, the value of Residual and RMS errors might be too high which might be caused by inaccurate coordinate of GCP, location of GCP on the map not obvious enough, or poor quality of the map you would like to rectify.

If the value of the RMS error in a GCP group is low, the sum of the RMS error will be low as well. That is to say, the rectification result is more accurate. However, you still need to check whether there is any residual too high, and you might need to delete or reset the GCP to get the best quality of rectification.

Therefore, if you want to get a more accurate rectification result, you can zoom the map to the appropriate scale in SuperGIS DataRectifier to add the GCP to the needed location (real-world coordinates). Also, you need to check whether the location is at the center of the GCP cross and whether the GCPs are distributed equally on the map. If there is any GCP with the high value of residual, please delete it and add a new GCP to decrease the residual and the sum of RMS errors of each group of GCPs to obtain a better rectification result.