Image geo-reference
This process is to establish the relationship between page coordinates (i.e. x,y) of a planar map of image with
known real-world coordinates (i.e. longitude/latitude, UTM, etc). Typically, ground control points (GCPs) can be
collected with GPS technique. The collected GCPs can be used to geo-reference the images. A digital orthophoto
quadrangle (DOQ) is a computer-generated image of an aerial photograph in which image displacement caused
by terrain relief and camera tilts has been removed. It combines the image characteristics of a photograph with the
geometric qualities of a map. All DOQ’s are referenced to the North American Datum of 1983 (NAD83) and cast
on the Universal Transverse Mercator (UTM) projection. Primary (NAD83) and secondary (NAD27) datum
coordinates for the upper left pixel are included in the header to allow users to spatially reference other digital
data with the DOQ. So, Digital Ortho Quarter Quads (DOQQ's) can be also used to geo-reference the images.