Abstract: A process for extracting the precise perimeter of buildings from down-looking terrain images. The process works for any rectilinear building shape, and no restrictions are placed on the orientation or scale of the buildings within an image. The process has the advantages of robustness and execution speed. The process is robust in that it can extract building perimeters from a digitized image in the presence of multiple noise sources. The execution speed is proportional to N+M, where the size of the image is N by M pixels.

Abstract: A method of searching a plural pre-registered data lines in which each of the data lines has data units such as letters and an index number, and of registering a new data line which also has data units among the data lines. The index number indicates the number of the coinciding letters from the first letter between each of the data lines and a data line one preceding to the data line. The method includes the step of comparing the new data line with the first ordered data line among the pre-registered data lines according to alphabetical order. If the new data line is not the same as the first ordered data line, other pre-registered data lines are searched in order to determine an order of the new data line to be registered among the pre-registered data lines.