The default settings for collecting GCPs (automatic and manual) are designed to be precise and accurate. However, sometimes you can only ensure the precision of your GCPs, and not the accuracy. An example of this is when you want to orthorectify a high-resolution satellite image of a remote land area for which accurate, high-resolution reference data does not exist, and the best available georeferenced source is a medium-resolution image or vector.
For example, collecting a GCP on a high-resolution image (≅ 1 meter to 5 meter) from a medium-resolution georeferenced source (15 meter to 30 meter) will produce GCP collection that is precise; however, the accuracy of the collected GCPs will be reduced. In such a case, it is good practice to set the accuracy of the GCPs so that the math-model computations can account for the reduced accuracy of the georeferenced source.
For information on setting new default values, see Setting the accuracy values.
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