Hi Devin, During RPC orthorectification, even one GCP can make a big difference in terms of removing any bias that might exist in the RPC information that comes with the images. You can manually enter that one GCP as part of the RPC Ortho Workflow. The information that is needed is to know accurately where the point is in the image, and then also the accurate x and y map or lat/long locations, and elevation for the point. You need to have quite accurate values, or there is no point in using the GCP. It sounds like your research coordinator has given you an image of your study area, with accurate x, y, and z locations for some points. If you can find those same locations in your unorthorectified image, then you can manually enter the x, y, and z values from the data you were given, and manually enter those when you are setting up GCPs for your orthorectification of your other image of the same area. If there are a lot of points, you don't necessarily need to use them all for orthorectification. Just a few will probably do a good job, if you can find them clearly in your image, and if you have accurate x, y, and z locations for those points. I hope this helps. Peg