User Manual - pancroma

50. Automatic Image Registration of Six Band Files________________________________________________________In order to use the PANCROMA TM Landsat gap-filling and cloud mask utilitiesyou must provide two image sets. The first set, which I call the Reference set,typically has some feature that needs to be corrected using data from a seconddata set, that I call the Adjust set. For example, the Reference set may havegaps, that is, missing data as a result of the failure of the Landsat Scan LineCorrector (SLC) in 2003. PANCROMA TM gap filling utilities use the data in animage set collected prior to the failure of the SLC to fill in or to compute theimage information that should go into the gaps. Likewise the Reference imagemay not suffer SLC-off gaps but may have considerable cloud cover. In this casePANCROMA TM cloud mask utilities can detect and replace the clouds with blackpixels, so that they can be subsequently filled in from a suitable Adjust data setwithout clouds.In either case, the Reference and the Adjust data sets must be perfectly coregisteredor matched so that the data can be transferred from the Adjust set tothe Reference set seamlessly, producing a natural looking image.PANCROMA TM provides a collection of utilities to produce this registration.These utilities often contain the following elements:• Compute Maximum Extents – this utility determines the maximum overlapbetween the Reference and Adjust data sets and specifies this overlap bycomputing the corner coordinates that define the overlap• Image Rescale. Sometimes the Reference and Adjust images do nothave the same scale factor. Landsat band images for example can haveeither 30m or 28.5m resolution. In this case the images must be rescaledso that the two match, i.e. the 28.5m image must be rescaled to 30mresolution• Image Subsetting. Next the two images must be cropped according to theMaximum Extents corner coordinates so that both images have the samelatitude and longitude boundaries• Row and Column Count Rationalization. The images get a final check tocorrect any off-by-one row or column discrepancies resulting fromrounding errors when recomputing row and column counts during anyrescaling and when mapping the corner latitude and longitude values totheir corresponding row and column values.Formerly, this process was done using four separate, semi-manual utilities. Anew PANCROMA TM utility conducts these operations automatically, saving timeand reducing the probability of making an error in the process. In order to use136