Design for Data Extraction from Digitized Contours

摘要

The problem addressed by this exercise is the extraction of a sequence of points (ranges) along specified tracks (generally radials emanating from a given point) which intersect digitized contour lines (of e.g., bathymetry), along with the associated contour values. The points are then sorted to provide the contour values as a function of range along the sequence of radials. The digitized contours and radials are specified as a sequence of (x, y,) longitude, latitude pairs. A Cartesian geometry is assumed. Since distances are computed in the standard Cartesian way, it is totally irrelevant whether the radials and contours are specified in terms of an absolute origin or in terms of a local relative origin. This latter feature of course has advantages when the absolute coordinates are sensitive. In addition, the method makes no assumption about whether the contours are closed or open in the universe under construction.