User Manual - pancroma

You will need three control points for the registration. Select the first one bymoving your cursor over it on the base image and clicking on it. Now locate thecorresponding point on the adjust image and click on it. The second image willbe adjusted during the registration process while the base image will remainunchanged. Return to the base image and click on the second point. Find itscorresponding point on the adjust image and click on it. Repeat for the thirdpoint. (Note that an internal toggle enforces the correct point entry order.)Each time you click on a point, its row and column coordinates will be displayedon the Image Registration form. If you make a mistake you can clear the textboxes or else just keep clicking, as the algorithm will just keep cycling until youstop. Once you have your three pairs of points recorded, select ‘Enter’ to startthe computation.PANCROMA TM will first compute the transformation coordinates based on thecontrol point data that you have input. It will then apply the transformation to theadjust image. Since the transformation will not generally be a one-to-onemapping, narrow gaps will occur after the transformation. PANCROMA TM will fillthese gaps using a Laplacian transformation interpolation.Although the adjust image is generally mapped to the base image, there is acommon case where the base image must also be adjusted. The transformationmay compute negative adjust image row and column coordinates if the adjustimage must be moved west and north. This cannot be, so the necessary offset isapplied to both the base and adjust images to prevent this from happening. Theresult is extra padding pixels added to the base image such that its row andcolumn counts are increased by the offset amount. The UTM corner coordinatesare then corrected to keep everything in order. If the base image adjustmentgoes the other way, the offset is not needed.After the registration is computed, the graphics windows will display the baseimage, adjusted if necessary as explained above and the transformed adjustimage. The images can be saved in GeoTiff format by selecting ‘File’ | ‘Save’ |‘Save Grayscale Image’ | ‘GeoTiff’. You will be asked to supply a base file name.When you do so and select ‘Save’, both images will be saved. They can be usedfor other purposes, or can be processed using future PANCROMA TM utilities, likeimage merge. The straightforward linear transformation can yield excellentresults for Landsat images. Some examples of the quality of the registration canbe seen in the images below.178