I've read Esri documentation about tfwx and still don't get it. When would an approximate Affine transformation be generated, or why is it an "approximate"?
I did this experiment:
(1) Load a tif image (a scanned map), load the control point file, run Rectify. A new tif created with a tfw file. There is no transformation stored in the asscciated aux.xml file.
(2) Load the same tif image, load the same control point file, run Update Georeferencing. tfwx is created and there is transformation stored in the associated aux.xml file.
I expected the numbers in the tfw file and the tfwx file be the same, since they are generated from the same scanned image using the same control point file, but the numbers in the two files are slightly different. Where is the discrepancy from? Also, does it imply that Rectify creates an exact Affine transformation, and Update Georeferencing creates an approximate one?
Many thanks.
Wei-Hsin Fu