1 files changed, 103 insertions, 0 deletions
diff --git a/src/gauss.cpp b/src/gauss.cpp
new file mode 100644
index 00000000..2db713ad
--- /dev/null
+++ b/src/gauss.cpp
@@ -0,0 +1,103 @@
+/*
+** libproj -- library of cartographic projections
+**
+** Copyright (c) 2003   Gerald I. Evenden
+*/
+/*
+** Permission is hereby granted, free of charge, to any person obtaining
+** a copy of this software and associated documentation files (the
+** "Software"), to deal in the Software without restriction, including
+** without limitation the rights to use, copy, modify, merge, publish,
+** distribute, sublicense, and/or sell copies of the Software, and to
+** permit persons to whom the Software is furnished to do so, subject to
+** the following conditions:
+**
+** The above copyright notice and this permission notice shall be
+** included in all copies or substantial portions of the Software.
+**
+** THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+** EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+** MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+** IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+** CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+** TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+** SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+#define PJ_LIB__
+
+#include <math.h>
+#include <stdlib.h>
+
+#include "projects.h"
+
+#define MAX_ITER 20
+
+namespace { // anonymous namespace
+struct GAUSS {
+    double C;
+    double K;
+    double e;
+    double ratexp;
+};
+} // anonymous namespace
+#define DEL_TOL 1e-14
+
+static double srat(double esinp, double ratexp) {
+    return(pow((1.-esinp)/(1.+esinp), ratexp));
+}
+
+void *pj_gauss_ini(double e, double phi0, double *chi, double *rc) {
+    double sphi, cphi, es;
+    struct GAUSS *en;
+
+    if ((en = (struct GAUSS *)malloc(sizeof(struct GAUSS))) == nullptr)
+        return (nullptr);
+    es = e * e;
+    en->e = e;
+    sphi = sin(phi0);
+    cphi = cos(phi0);  cphi *= cphi;
+    *rc = sqrt(1. - es) / (1. - es * sphi * sphi);
+    en->C = sqrt(1. + es * cphi * cphi / (1. - es));
+    if (en->C == 0.0) {
+        free(en);
+        return nullptr;
+    }
+    *chi = asin(sphi / en->C);
+    en->ratexp = 0.5 * en->C * e;
+    en->K = tan(.5 * *chi + M_FORTPI) / (
+        pow(tan(.5 * phi0 + M_FORTPI), en->C) *
+        srat(en->e * sphi, en->ratexp)  );
+    return ((void *)en);
+}
+
+LP pj_gauss(projCtx ctx, LP elp, const void *data) {
+    const struct GAUSS *en = (const struct GAUSS *)data;
+    LP slp;
+    (void) ctx;
+
+    slp.phi = 2. * atan( en->K *
+        pow(tan(.5 * elp.phi + M_FORTPI), en->C) *
+        srat(en->e * sin(elp.phi), en->ratexp) ) - M_HALFPI;
+    slp.lam = en->C * (elp.lam);
+    return(slp);
+}
+
+LP pj_inv_gauss(projCtx ctx, LP slp, const void *data) {
+    const struct GAUSS *en = (const struct GAUSS *)data;
+    LP elp;
+    double num;
+    int i;
+
+    elp.lam = slp.lam / en->C;
+    num = pow(tan(.5 * slp.phi + M_FORTPI)/en->K, 1./en->C);
+    for (i = MAX_ITER; i; --i) {
+        elp.phi = 2. * atan(num * srat(en->e * sin(slp.phi), -.5 * en->e))
+            - M_HALFPI;
+        if (fabs(elp.phi - slp.phi) < DEL_TOL) break;
+            slp.phi = elp.phi;
+    }
+    /* convergence failed */
+    if (!i)
+        pj_ctx_set_errno(ctx, PJD_ERR_NON_CONV_INV_MERI_DIST);
+    return (elp);
+}