1 files changed, 53 insertions, 0 deletions
diff --git a/src/projections/collg.cpp b/src/projections/collg.cpp
new file mode 100644
index 00000000..7904de29
--- /dev/null
+++ b/src/projections/collg.cpp
@@ -0,0 +1,53 @@
+#define PJ_LIB__
+
+#include <math.h>
+
+#include "proj.h"
+#include "projects.h"
+
+PROJ_HEAD(collg, "Collignon") "\n\tPCyl, Sph";
+#define FXC 1.12837916709551257390
+#define FYC 1.77245385090551602729
+#define ONEEPS  1.0000001
+
+
+static XY s_forward (LP lp, PJ *P) {           /* Spheroidal, forward */
+    XY xy = {0.0,0.0};
+    (void) P;
+    if ((xy.y = 1. - sin(lp.phi)) <= 0.)
+        xy.y = 0.;
+    else
+        xy.y = sqrt(xy.y);
+    xy.x = FXC * lp.lam * xy.y;
+    xy.y = FYC * (1. - xy.y);
+    return (xy);
+}
+
+
+static LP s_inverse (XY xy, PJ *P) {           /* Spheroidal, inverse */
+    LP lp = {0.0,0.0};
+    lp.phi = xy.y / FYC - 1.;
+    if (fabs(lp.phi = 1. - lp.phi * lp.phi) < 1.)
+        lp.phi = asin(lp.phi);
+    else if (fabs(lp.phi) > ONEEPS) {
+        proj_errno_set(P, PJD_ERR_TOLERANCE_CONDITION);
+        return lp;
+    } else {
+        lp.phi = lp.phi < 0. ? -M_HALFPI : M_HALFPI;
+    }
+
+    if ((lp.lam = 1. - sin(lp.phi)) <= 0.)
+        lp.lam = 0.;
+    else
+        lp.lam = xy.x / (FXC * sqrt(lp.lam));
+    return (lp);
+}
+
+
+PJ *PROJECTION(collg) {
+    P->es = 0.0;
+    P->inv = s_inverse;
+    P->fwd = s_forward;
+
+    return P;
+}