pj_deriv.cpp

projapi是一个关于GIS行业投影转换的程序库

#include "stdafx.h"

/* dervative of (*P->fwd) projection */
#ifndef lint
static const char SCCSID[]="@(#)pj_deriv.c	4.4	93/06/12	GIE	REL";
#endif
#define PJ_LIB__
#include "projects.h"
#include <math.h>
	
int pj_deriv(LP lp, double h, PJ *P, struct DERIVS *der) 
{
	XY t;

	lp.lam += h;
	lp.phi += h;
	if (fabs(lp.phi) > HALFPI) return 1;
	h += h;
	t = (*P->fwd)(lp, P);
	if (t.x == HUGE_VAL) return 1;
	der->x_l = t.x; der->y_p = t.y; der->x_p = -t.x; der->y_l = -t.y;
	lp.phi -= h;
	if (fabs(lp.phi) > HALFPI) return 1;
	t = (*P->fwd)(lp, P);
	if (t.x == HUGE_VAL) return 1;
	der->x_l += t.x; der->y_p -= t.y; der->x_p += t.x; der->y_l -= t.y;
	lp.lam -= h;
	t = (*P->fwd)(lp, P);
	if (t.x == HUGE_VAL) return 1;
	der->x_l -= t.x; der->y_p -= t.y; der->x_p += t.x; der->y_l += t.y;
	lp.phi += h;
	t = (*P->fwd)(lp, P);
	if (t.x == HUGE_VAL) return 1;
	der->x_l -= t.x; der->y_p += t.y; der->x_p -= t.x; der->y_l += t.y;
	der->x_l /= (h += h);
	der->y_p /= h;
	der->x_p /= h;
	der->y_l /= h;
	return 0;
}