# Locating a point on a spherical surface relative to a spherical polygon of arbitrary shape

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## Abstract

An algorithm for determining if any given point,*P*, on the surface of a sphere is located inside, outside, or along the border of an arbitrary spherical polygon,*S*, is described. The polygon is described by specifying coordinates of its vertices, and coordinates of some point*X* which is known to lie within*S*. The algorithm is based on the principle that an arc joining*X* and*P* will cross the border of*S* an odd number of times if*P* lies outside*S*, and an even number of times if*P* lies within*S*. The algorithm has been implemented as a set of FORTRAN subroutines, and a listing is provided. The algorithm and subroutine package can be used with spherical polygons containing holes, or with composited spherical polygons.

## Key words

Spherical polygon locate sort algorithm FORTRAN subroutine## Preview

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## References

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