Using a math model with images

A math model is a mathematical relationship used to correlate the pixels of an image to correct locations on the ground accounting for known distortions. Different sensors require different math models to correct the distortions.

Math models can come from a variety of sources. For example, QuickBird, Ikonos, and OrbView imagery comes typically with a text file that contains rational-function coefficients called image geometry model (IGM) or rapid positioning capability (RPC), which Focus uses to define a rational-function math model. You can build a math model in OrthoEngine and export it as a segment of the file containing a raw image. CATALYST Professional also features algorithms you can run to build a math model. In the Algorithm Librarian, the following algorithms are available to build a math model.

When you open an image containing a math-model segment, you can select to use the file georeferencing or the math model. When you select file georeferencing, the image opens in a layer in an area on the Maps tab using the georeferencing saved in the file or, if no georeferencing is available, pixel-based georeferencing. When you select the math model, the image displays as a layer and, under Maps, the label changes from Area to Math Model Area. In the math-model area, the image displays without correction in the viewer, but accurate ground coordinates are calculated for each pixel using the pixel and line coordinates, the math model, and the digital elevation model (DEM), or an approximate elevation value that you provide.

The advantage of using the math model is that you can display geocoded coordinates, overlay geocoded vectors, and digitize geocoded three-dimensional vectors on the raw image instead of going through the potentially time-consuming, labor-intensive process of orthorectifying or geometrically correcting the imagery. This process is also known as monorestitution.

To use a math model with images