GCPWorks is able to read USGS DLG-3 Optional Format data files, so no special data conversion is required. After selecting Full Processing, Polynomial Model, and Vectors, accept the setup. Load the uncorrected image and select the vector data.
Following this there are two options. One is to ``Define the Georeferenced Area'' by setting the bounds of the area of interest, and the other is to ``Select Georeferenced Database''. If no output file has been setup to register into, then the user will have to select the ``Define Georeferenced Area'' panel. The area of interest defined by one of these methods will determine the area of the vector coverage shown in the georeferenced overview window.
Next, GCPs can be collected using the ``GCP Collection'' panel. There are some special features available when performing image to vector tie-down. After three GCPs have been collected, the vector data will be warped, according to the current polynomial model, into the uncorrected image subwindow. This warping provides immediate feedback on the current polynomial fit.
It is also possible to collect both the uncorrected and the corrected portions of a GCP within the uncorrected image window. The uncorrected cursor (yellow crosshair) can be moved by dragging it with the left mouse button depressed. It should be placed on the GCP location in the uncorrected imagery. The corrected cursor (red crosshair) may also be dragged in the uncorrected window by dragging with the RIGHT mouse button depressed. It should be placed on the GCP location in the corrected imagery which appears in the uncorrected image window. This whole process of GCP collection is the equivalent of choosing GCPs using the cursors in their own windows.
Once the GCPs have been collected it is possible to proceed with pre-registration and final registration.