polyconic.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include <u.h>
#include <libc.h>
#include "map.h"

int
Xpolyconic(struct place *place, double *x, double *y)
{
	double r, alpha;
	double lat2, lon2;
	if(fabs(place->nlat.l) > .01) {
		r = place->nlat.c / place->nlat.s;
		alpha = place->wlon.l * place->nlat.s;
		*y = place->nlat.l + r*(1 - cos(alpha));
		*x = - r*sin(alpha);
	} else {
		lon2 = place->wlon.l * place->wlon.l;
		lat2 = place->nlat.l * place->nlat.l;
		*y = place->nlat.l * (1+(lon2/2)*(1-(8+lon2)*lat2/12));
		*x = - place->wlon.l * (1-lat2*(3+lon2)/6);
	}
	return(1);
}

proj
polyconic(void)
{
	return(Xpolyconic);
}