1 files changed, 77 insertions, 0 deletions
diff --git a/src/projections/PJ_hammer.cpp b/src/projections/PJ_hammer.cpp
new file mode 100644
index 00000000..d4caa656
--- /dev/null
+++ b/src/projections/PJ_hammer.cpp
@@ -0,0 +1,77 @@
+#define PJ_LIB__
+
+#include <errno.h>
+#include <math.h>
+
+#include "proj.h"
+#include "projects.h"
+
+PROJ_HEAD(hammer, "Hammer & Eckert-Greifendorff")
+    "\n\tMisc Sph, \n\tW= M=";
+
+#define EPS 1.0e-10
+
+namespace { // anonymous namespace
+struct pj_opaque {
+    double w;
+    double m, rm;
+};
+} // anonymous namespace
+
+
+static XY s_forward (LP lp, PJ *P) {           /* Spheroidal, forward */
+    XY xy = {0.0,0.0};
+    struct pj_opaque *Q = static_cast<struct pj_opaque*>(P->opaque);
+    double cosphi, d;
+
+    d = sqrt(2./(1. + (cosphi = cos(lp.phi)) * cos(lp.lam *= Q->w)));
+    xy.x = Q->m * d * cosphi * sin(lp.lam);
+    xy.y = Q->rm * d * sin(lp.phi);
+    return xy;
+}
+
+
+static LP s_inverse (XY xy, PJ *P) {           /* Spheroidal, inverse */
+    LP lp = {0.0,0.0};
+    struct pj_opaque *Q = static_cast<struct pj_opaque*>(P->opaque);
+    double z;
+
+    z = sqrt(1. - 0.25*Q->w*Q->w*xy.x*xy.x - 0.25*xy.y*xy.y);
+    if (fabs(2.*z*z-1.) < EPS) {
+        lp.lam = HUGE_VAL;
+        lp.phi = HUGE_VAL;
+        proj_errno_set(P, PJD_ERR_LAT_OR_LON_EXCEED_LIMIT);
+    } else {
+        lp.lam = aatan2(Q->w * xy.x * z,2. * z * z - 1)/Q->w;
+        lp.phi = aasin(P->ctx,z * xy.y);
+    }
+    return lp;
+}
+
+
+PJ *PROJECTION(hammer) {
+    struct pj_opaque *Q = static_cast<struct pj_opaque*>(pj_calloc (1, sizeof (struct pj_opaque)));
+    if (nullptr==Q)
+        return pj_default_destructor (P, ENOMEM);
+    P->opaque = Q;
+
+    if (pj_param(P->ctx, P->params, "tW").i) {
+        if ((Q->w = fabs(pj_param(P->ctx, P->params, "dW").f)) <= 0.)
+            return pj_default_destructor (P, PJD_ERR_W_OR_M_ZERO_OR_LESS);
+    } else
+        Q->w = .5;
+    if (pj_param(P->ctx, P->params, "tM").i) {
+        if ((Q->m = fabs(pj_param(P->ctx, P->params, "dM").f)) <= 0.)
+            return pj_default_destructor (P, PJD_ERR_W_OR_M_ZERO_OR_LESS);
+    } else
+        Q->m = 1.;
+
+    Q->rm = 1. / Q->m;
+    Q->m /= Q->w;
+
+    P->es = 0.;
+    P->fwd = s_forward;
+    P->inv = s_inverse;
+
+    return P;
+}