OrthoEngine can use image correlation to identify the pixel and line locations in the raw image that correspond to features in the georeferenced image or to the georeferenced positions on the chips. It is this image correlation that OrthoEngine uses in automatic collection of ground control points (GCP).
To collect GCPs automatically
To specify multiple channels, use a comma-delimited list.
When collecting GCPs, the Grid option is preferred because the Susan option finds candidates on building corners that may not be represented in the DEM, leading to GCPs with higher residuals due to height errors.
If no value is specified for this parameter, the default method, NCC, is used.
When the two images being matched have similar gray values and appearances, NCC generally produces acceptable results. When there is a rotation or image-size error in the initial math models, NCC may produce better matching results than FFTP. Because the template size that NCC uses is smaller than the one used by FFTP, this method also typically generates faster results.
For more consistently accurate results, FFTP is recommended. This method uses a larger template size than NCC and, because it works in the frequency domain, it looks at the patterns of details in the image rather than the gray values in a small neighborhood, which NCC uses. This makes FFTP more robust than NCC in cases where there is a large brightness difference between images or when a major land-use change has occurred between the images and allows it to better match images of the same area from different sensors or spectral bands.
In the Search radius box, type a number to define the search radius around the kernel.
For example, to enter 100 pixels, type 100, and then select PIXEL.
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