Name

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      SPHIC

Purpose

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      Compute intersection points of two circles on a unit sphere.

Category

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Calling Sequence

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      sphic, ln1,lt1,r1, ln2,lt2,r2, lnp1,ltp1, lnp2,ltp2, flag

Inputs

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      ln1 = longitude of circle 1 center. in
      lt1 = latitude of circle 1 center. in
      r1 = radius of circle 1. in
            Angle along sphere surface.
      ln2 = longitude of circle 2 center. in
      lt2 = latitude of circle 2 center. in
      r2 = radius of circle 2. in
            Angle along sphere surface.

Keyword Parameters

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Keywords

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        /DEGREES means all angles are in degrees, else radians.

Outputs

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      lnp1 = longitude of intersection 1. out
      ltp1 = latitude of intersection 1. out
      lnp2 = longitude of intersection 2. out
      ltp2 = latitude of intersection 2. out
      flag = -2: circles are the same, all points on both.
              -1: parallel circles, different radii, no int.
              0: non-parallel circles, no intersection.
              1: tangent circles, one intersection.
              2: circles intersect in two points.

Common Blocks

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Notes

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      Notes: if flag < 1 then returned intersection points
        are meaningless and may be undefined.
        If flag = 1 then both points are the same.

Modification History

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      R. Sterner. 13 Apr, 1988.
      R. Sterner. 14 Feb, 1991 --- to IDL V2 & slight changes.
  Copyright (C) 1988, Johns Hopkins University/Applied Physics Laboratory
  This software may be used, copied, or redistributed as long as it is not
  sold and this copyright notice is reproduced on each copy made. This
  routine is provided as is without any express or implied warranties
  whatsoever. Other limitations apply as described in the file disclaimer.txt.