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Sourcecode: r-cran-mapproj version File versions  Download package

harrison.c

/* RSB #include <u.h>
#include <libc.h>*/
#include "map.h"

static double v3,u2,u3,a,b; /*v=view,p=obj,u=unit.y*/

static int
Xharrison(struct place *place, double *x, double *y)
{
      double p1 = -place->nlat.c*place->wlon.s;
      double p2 = -place->nlat.c*place->wlon.c;
      double p3 = place->nlat.s;
      double d = b + u3*p2 - u2*p3;
      double t;
      if(d < .01)
            return -1;
      t = a/d;
      if(v3*place->nlat.s < 1.)
            return -1;
      *y = t*p2*u2 + (v3-t*(v3-p3))*u3;
      *x = t*p1;
      if(t < 0)
            return 0;
      if(*x * *x + *y * *y > 16)
            return -1;
      return 1;
}

proj
harrison(double r, double alpha)
{
      u2 = cos(alpha*RAD);
      u3 = sin(alpha*RAD);
      v3 = r;
      b = r*u2;
      a = 1 + b;
      if(r<1.001 || a<sqrt(r*r-1))
            return 0;
      return Xharrison;
}

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