On-the-Fly processing enables the server to perform both geometric and radiometric pixel based processes on the imagery as it is accessed. This processing can be for example applying a LUT (look up table) to change the color (a radiometric process) or re-projecting the data (a geometric process). There are a large range of processes that can be applied. Orthorectification is on example of a geometric process. For an image to be orthorectified a sensor model with orientation parameters and a DEM need to be available. The most common sensor models supported are the Standard Frame (primarily used for frame based aerial cameras such as DSS, UltraCam, DMC) and RPC (used for many satellites such as QuickBird and Ikonos). The frame based sensor models require parameters such as the exterior orientation of the each frame, focal length, camera distortion and interior orientation. The Digital Elevation Model can be a raster (such as a 32bit TIF or FLT) or another image service serving elevation data. Different raster types can be used to set the ISDef (in V9.3) or MosaicDataset (in V10). These import the orientation data etc and set up the processes. As a users access an area of interest the system determines which images should participate and applies the appropriate process on the fly only for the pixels that need to be viewed. This processing is very fast. For Orthorectification it extracts the required elevation data and then applies the Orthorectification processes based on the provided sensor model and parameters. V10 is very similar but provides more flexibility in defining additional sensor models. In V10 all this capability is also part of the desktop.
