diff options
Diffstat (limited to 'src/PJ_eck4.c')
| -rw-r--r-- | src/PJ_eck4.c | 47 |
1 files changed, 47 insertions, 0 deletions
diff --git a/src/PJ_eck4.c b/src/PJ_eck4.c new file mode 100644 index 00000000..9784a1c4 --- /dev/null +++ b/src/PJ_eck4.c @@ -0,0 +1,47 @@ +#ifndef lint +static const char SCCSID[]="@(#)PJ_eck4.c 4.1 94/02/15 GIE REL"; +#endif +#define PJ_LIB__ +#include <projects.h> +PROJ_HEAD(eck4, "Eckert IV") "\n\tPCyl, Sph."; +#define C_x .42223820031577120149 +#define C_y 1.32650042817700232218 +#define RC_y .75386330736002178205 +#define C_p 3.57079632679489661922 +#define RC_p .28004957675577868795 +#define EPS 1e-7 +#define NITER 6 +FORWARD(s_forward); /* spheroid */ + double p, V, s, c; + int i; + + p = C_p * sin(lp.phi); + V = lp.phi * lp.phi; + lp.phi *= 0.895168 + V * ( 0.0218849 + V * 0.00826809 ); + for (i = NITER; i ; --i) { + c = cos(lp.phi); + s = sin(lp.phi); + lp.phi -= V = (lp.phi + s * (c + 2.) - p) / + (1. + c * (c + 2.) - s * s); + if (fabs(V) < EPS) + break; + } + if (!i) { + xy.x = C_x * lp.lam; + xy.y = lp.phi < 0. ? -C_y : C_y; + } else { + xy.x = C_x * lp.lam * (1. + cos(lp.phi)); + xy.y = C_y * sin(lp.phi); + } + return (xy); +} +INVERSE(s_inverse); /* spheroid */ + double c; + + lp.phi = aasin(xy.y / C_y); + lp.lam = xy.x / (C_x * (1. + (c = cos(lp.phi)))); + lp.phi = aasin((lp.phi + sin(lp.phi) * (c + 2.)) / C_p); + return (lp); +} +FREEUP; if (P) pj_dalloc(P); } +ENTRY0(eck4); P->es = 0.; P->inv = s_inverse; P->fwd = s_forward; ENDENTRY(P) |