Orthorectification of WorldView-2 satellite imagery, of the Cape Poinsett area, Budd Coast, Antarctica, captured 2 November 2013

Given that there were no accurate ground control points or digital elevation models available within the image area it was decided that the orthorectification be carried out using the fast mode orthorectification process which derives a model from the RPC co-efficients. Rational polynomial coefficients (RPCs) model the ground-to-image relationship as a third-order, rational, ground-to-image polynomial. The RPC orthorectification process works on a pixel-by-pixel basis to provide correct ground locations, so it can take a significant amount of processing time.

An alternative method to the standard RPC orthorectification is a "fast mode" orthorectification. This method works by sacrificing accuracy for speed, since processing time is much faster but the results are slightly less accurate. Instead of solving the RPC equation for each pixel, the fast mode orthorectification solves for a grid of points spaced throughout the image and triangulates a warp between the points.

This approach assumes that the geometric accuracy of the WorldView-2 image based on its RPC and attitude information is more accurate than a polynomial correction based on inaccurate ground control points. In this orthorectification approach the image is assumed to be in the correct location (at sea level) and topographic relief distortions are not removed.