thomas@eleazar.dartmouth.edu (Thomas Summerall) (07/27/90)
A geography professor here has the following problem: If he has a map of a country, with each state as a separate object, and he overlays a map of rainfall, with each rainfall area as a separate object, is there software whic will tell him the area of the intersection of a state object with a rainfall object? I tried Claris Cad, Canvas, and Dreams, but none would do it. Thanks, Thomas Summerall
tim@walt.cc.utexas.edu (Tim Eakin) (07/31/90)
In article <23374@dartvax.Dartmouth.EDU> thomas@eleazar.dartmouth.edu (Thomas Summerall) writes: >A geography professor here has the following problem: If he has a map of >a country, with each state as a separate object, and he overlays a map of >rainfall, with each rainfall area as a separate object, is there software >whic will tell him the area of the intersection of a state object with a >rainfall object? One problem may be that there are so many different types of projections. Each would require its own algorithm. In the usual Mercator conformal projection you can get an overlap in the northern part of a state and one in the southern part which are equal in map area but unequal in actual surface area, and vice versa. Any results obtained from generic software that assumes isotropic preservation of area in projections would not be too meaningful. All this assumes of course that the professor's maps are planar. If he is working with 3-D objects that lie on the surface of a sphere, then his overlap areas will all be linearly related.