When you select to view ground control points (GCP) as displacement lines, Focus constructs a line consisting of two vertices for each GCP. The first vertex is computed from the stored pixel-and-line coordinates (image coordinates) and the second vertex is derived from the stored geographic coordinates (ground coordinates). Displacement lines show you how far each image location that forms a GCP must be moved to agree with the reference data. A longer displacement line indicates that the source image must be warped more at that location compared to another location with a shorter displacement line.
If the source file has a real projection, this projection is used, along with the upper-left coordinate and georeferencing (including rotation) of the file, and the stored pixel-and-line coordinates, to compute new geographic coordinates for the first vertex. The second vertex is derived directly from the stored geographic coordinates. If the source file does not have an associated math model, the generated vector layer is created with the same projection as the georeferencing of the file. If there is at least one math model, you can select the georeferencing from the math model to convert the image coordinates to geographic coordinates for the first vertex.
To view GCPs as displacement lines
The layer is displayed with GCPs derived from the georeferencing of the file.
The Select Layer Georeferencing window appears. To select the math model georeferencing information, see Using the math model for georeferencing; otherwise, click OK.
The layer is displayed with GCPs derived from the georeferencing of the math model.
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