User Manual - pancroma

Landsat scenes. Different Landsat images taken of the same scene posses ahigh degree of commonality. However they can also differ in the following ways:• Corner coordinates generally will not match exactly• Row and column counts will usually be different• Obvious transnational differences will exist with respect to the upper leftcorner of the image (which is commonly taken as the 0,0 row and columncoordinate)• Scales may differ - some Landsat scenes have a resolution of 30m perpixel while earlier images have a slightly higher resolution of 28.5m/pixelSometimes it is necessary to adjust two similar images so that these and otherdifferences are minimized and the two images align, for example in gap-filling,cloud masking and creating image mosaics.Image registration is accomplished by conducting one or more imagetransformations to one of the images so that it matches the other. There aremany types of transformations, for example linear, affine, approximations,piecewise methods, etc. They all work by building transformation functions usingreference points (called ground control points or GCPs) on both images that areknown to describe the same point on the earth’s surface. The transformationfunctions contain parameters or coefficients that are constructed usingmathematical models describing the expected differences between the twoimages. PANCROMA TM uses a relatively simple linear transformation in itsgeneral registration function. Although simple in principle, its implementation incode is of course be less than simple. Linear transformations are generallyappropriate for images that are acquired far from the earth’s surface, and for datasets like Landsat are projected to a common datum and are oriented ‘north is up’.To use the utility, you must have two images that have at least some commonarea, and preferably a high percentage of overlap. Start by Selecting ‘File’ |‘Open’ and opening two GeoTiff band files that you wish to register. The filesshould use the UTM projection and have the same datum and be oriented so thatnorth is up. The first file that you open will be the ‘base’ file. The second file(adjust image) will be the ‘adjust’ file, i.e. the one that is transformed to match thebase image. Now select ‘PreProcess’ | ‘Register Images’ | ‘LinearTransformation Two Images’.A data entry box will be become visible. The next step is to select the groundcontrol points (GCPs). GCPs are points on the base and adjust image that youcan clearly identify as having precisely the same location. The easiest way toselect such points is to select those with the same latitude and longitudecoordinates. The UTM coordinates for both the base and adjust images aredisplayed in the Main Window as you scroll over the base and adjust images.You can also select ground features for GCPs.175