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#define PJ_LIB__
#include <errno.h>
#include <projects.h>
PROJ_HEAD(ocea, "Oblique Cylindrical Equal Area") "\n\tCyl, Sph"
"lonc= alpha= or\n\tlat_1= lat_2= lon_1= lon_2=";
struct pj_opaque {
double rok;
double rtk;
double sinphi;
double cosphi;
double singam;
double cosgam;
};
static XY s_forward (LP lp, PJ *P) { /* Spheroidal, forward */
XY xy = {0.0,0.0};
struct pj_opaque *Q = P->opaque;
double t;
xy.y = sin(lp.lam);
t = cos(lp.lam);
xy.x = atan((tan(lp.phi) * Q->cosphi + Q->sinphi * xy.y) / t);
if (t < 0.)
xy.x += M_PI;
xy.x *= Q->rtk;
xy.y = Q->rok * (Q->sinphi * sin(lp.phi) - Q->cosphi * cos(lp.phi) * xy.y);
return xy;
}
static LP s_inverse (XY xy, PJ *P) { /* Spheroidal, inverse */
LP lp = {0.0,0.0};
struct pj_opaque *Q = P->opaque;
double t, s;
xy.y /= Q->rok;
xy.x /= Q->rtk;
t = sqrt(1. - xy.y * xy.y);
lp.phi = asin(xy.y * Q->sinphi + t * Q->cosphi * (s = sin(xy.x)));
lp.lam = atan2(t * Q->sinphi * s - xy.y * Q->cosphi,
t * cos(xy.x));
return lp;
}
PJ *PROJECTION(ocea) {
double phi_0=0.0, phi_1, phi_2, lam_1, lam_2, lonz, alpha;
struct pj_opaque *Q = pj_calloc (1, sizeof (struct pj_opaque));
if (0==Q)
return pj_default_destructor (P, ENOMEM);
P->opaque = Q;
Q->rok = 1. / P->k0;
Q->rtk = P->k0;
/*If the keyword "alpha" is found in the sentence then use 1point+1azimuth*/
if ( pj_param(P->ctx, P->params, "talpha").i) {
/*Define Pole of oblique transformation from 1 point & 1 azimuth*/
alpha = pj_param(P->ctx, P->params, "ralpha").f;
lonz = pj_param(P->ctx, P->params, "rlonc").f;
/*Equation 9-8 page 80 (http://pubs.usgs.gov/pp/1395/report.pdf)*/
Q->singam = atan(-cos(alpha)/(-sin(phi_0) * sin(alpha))) + lonz;
/*Equation 9-7 page 80 (http://pubs.usgs.gov/pp/1395/report.pdf)*/
Q->sinphi = asin(cos(phi_0) * sin(alpha));
/*If the keyword "alpha" is NOT found in the sentence then use 2points*/
} else {
/*Define Pole of oblique transformation from 2 points*/
phi_1 = pj_param(P->ctx, P->params, "rlat_1").f;
phi_2 = pj_param(P->ctx, P->params, "rlat_2").f;
lam_1 = pj_param(P->ctx, P->params, "rlon_1").f;
lam_2 = pj_param(P->ctx, P->params, "rlon_2").f;
/*Equation 9-1 page 80 (http://pubs.usgs.gov/pp/1395/report.pdf)*/
Q->singam = atan2(cos(phi_1) * sin(phi_2) * cos(lam_1) -
sin(phi_1) * cos(phi_2) * cos(lam_2),
sin(phi_1) * cos(phi_2) * sin(lam_2) -
cos(phi_1) * sin(phi_2) * sin(lam_1) );
/* take care of P->lam0 wrap-around when +lam_1=-90*/
if (lam_1 == -M_HALFPI)
Q->singam = -Q->singam;
/*Equation 9-2 page 80 (http://pubs.usgs.gov/pp/1395/report.pdf)*/
Q->sinphi = atan(-cos(Q->singam - lam_1) / tan(phi_1));
}
P->lam0 = Q->singam + M_HALFPI;
Q->cosphi = cos(Q->sinphi);
Q->sinphi = sin(Q->sinphi);
Q->cosgam = cos(Q->singam);
Q->singam = sin(Q->singam);
P->inv = s_inverse;
P->fwd = s_forward;
P->es = 0.;
return P;
}
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