80 lines
1.6 KiB
C
80 lines
1.6 KiB
C
#include <u.h>
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#include <libc.h>
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#include "map.h"
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static double
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quadratic(double a, double b, double c)
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{
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double disc = b*b - 4*a*c;
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return disc<0? 0: (-b-sqrt(disc))/(2*a);
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}
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/* for projections with meridians being circles centered
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on the x axis and parallels being circles centered on the y
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axis. Find the intersection of the meridian thru (m,0), (90,0),
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with the parallel thru (0,p), (p1,p2) */
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static int
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twocircles(double m, double p, double p1, double p2, double *x, double *y)
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{
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double a; /* center of meridian circle, a>0 */
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double b; /* center of parallel circle, b>0 */
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double t,bb;
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if(m > 0) {
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twocircles(-m,p,p1,p2,x,y);
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*x = -*x;
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} else if(p < 0) {
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twocircles(m,-p,p1,-p2,x,y);
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*y = -*y;
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} else if(p < .01) {
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*x = m;
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t = m/p1;
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*y = p + (p2-p)*t*t;
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} else if(m > -.01) {
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*y = p;
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*x = m - m*p*p;
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} else {
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b = p>=1? 1: p>.99? 0.5*(p+1 + p1*p1/(1-p)):
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0.5*(p*p-p1*p1-p2*p2)/(p-p2);
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a = .5*(m - 1/m);
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t = m*m-p*p+2*(b*p-a*m);
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bb = b*b;
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*x = quadratic(1+a*a/bb, -2*a + a*t/bb,
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t*t/(4*bb) - m*m + 2*a*m);
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*y = (*x*a+t/2)/b;
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}
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return 1;
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}
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static int
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Xglobular(struct place *place, double *x, double *y)
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{
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twocircles(-2*place->wlon.l/PI,
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2*place->nlat.l/PI, place->nlat.c, place->nlat.s, x, y);
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return 1;
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}
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proj
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globular(void)
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{
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return Xglobular;
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}
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static int
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Xvandergrinten(struct place *place, double *x, double *y)
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{
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double t = 2*place->nlat.l/PI;
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double abst = fabs(t);
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double pval = abst>=1? 1: abst/(1+sqrt(1-t*t));
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double p2 = 2*pval/(1+pval);
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twocircles(-place->wlon.l/PI, pval, sqrt(1-p2*p2), p2, x, y);
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if(t < 0)
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*y = -*y;
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return 1;
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}
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proj
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vandergrinten(void)
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{
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return Xvandergrinten;
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}
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