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Orthorectification and Georeferencing

Question asked by deleted-user-G61IFj8--dM5 on Jul 22, 2015
Latest reply on Jul 22, 2015 by hlzhang525

I would like to perform a change detection on two GeoEye images acquired a year apart. The images I received from DG are standard products and have not been orthorectified or georeferenced. DG has provided an .rpb file with each of the image files, but the only way I seem to be able to "use" them with the orthorectification tool in Image Analysis, is when I load the .til image file into my map document. 


Question 1: can someone explain to me the difference between the .til and the .tif files? If orthorectification can only be performed on the .til file, is that the file I need to be working with in my analysis?


In addition, I would like to georeference the two images so they are lying exactly one on top of the other. The area of interest is the same.


Question 2: Can I simply georeference the two images to one another vs. georeferencing them using a known/verified data set like an existing map or imagery basemap?


Thanks for any insight and help!