Georeferencing

An important aspect of browse imagery is the extent of the image and the georeferencing of the image. There are two primary ways in which the browse images are georeferenced.

Rectified

Each image is prerectified (or orthorectified) based on the best available referencing information. The result is an image that is stored in a projected coordinate system and typically has a border of NoData pixels. Typically such rectified images are generated in a suitable universal transverse Mercator (UTM) zone, in decimal degrees (WGS 84), or the Web Mercator projection. The disadvantage in using this method is that the black NoData pixels need to be clipped out. This can be done using footprints. It is optimal if the footprint can be provided by the system that rectifies the image; otherwise, processing time must be allocated for ArcGIS to calculate footprints.

Nonrectified

With browse images stored in nonrectified format, each image can be georeferenced for visualization by applying a simple projection using the four corner points of the image and projective transformation. In this case, the image is stored in simple image file coordinates and has the advantage of not including any NoData pixels. The definition of the projective transformation is best done using an associated AUX.XML file that defines the four image and ground coordinates. Such files can be generated quickly based on the information of the four corner coordinates and the size of the image. An example is provided in the Appendices.