diff options
Diffstat (limited to 'src/PJ_nell.c')
| -rw-r--r-- | src/PJ_nell.c | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/src/PJ_nell.c b/src/PJ_nell.c new file mode 100644 index 00000000..9473eff4 --- /dev/null +++ b/src/PJ_nell.c @@ -0,0 +1,34 @@ +#ifndef lint +static const char SCCSID[]="@(#)PJ_nell.c 4.1 94/02/15 GIE REL"; +#endif +#define PJ_LIB__ +#include <projects.h> +PROJ_HEAD(nell, "Nell") "\n\tPCyl., Sph."; +#define MAX_ITER 10 +#define LOOP_TOL 1e-7 +FORWARD(s_forward); /* spheroid */ + double k, V; + int i; + + k = 2. * sin(lp.phi); + V = lp.phi * lp.phi; + lp.phi *= 1.00371 + V * (-0.0935382 + V * -0.011412); + for (i = MAX_ITER; i ; --i) { + lp.phi -= V = (lp.phi + sin(lp.phi) - k) / + (1. + cos(lp.phi)); + if (fabs(V) < LOOP_TOL) + break; + } + xy.x = 0.5 * lp.lam * (1. + cos(lp.phi)); + xy.y = lp.phi; + return (xy); +} +INVERSE(s_inverse); /* spheroid */ + double th, s; + + lp.lam = 2. * xy.x / (1. + cos(xy.y)); + lp.phi = aasin(0.5 * (xy.y + sin(xy.y))); + return (lp); +} +FREEUP; if (P) pj_dalloc(P); } +ENTRY0(nell) P->es = 0; P->inv = s_inverse; P->fwd = s_forward; ENDENTRY(P) |