1 files changed, 74 insertions, 0 deletions
diff --git a/src/projections/mbtfpq.cpp b/src/projections/mbtfpq.cpp
new file mode 100644
index 00000000..b7c0eb16
--- /dev/null
+++ b/src/projections/mbtfpq.cpp
@@ -0,0 +1,74 @@
+#define PJ_LIB__
+
+#include <math.h>
+
+#include "proj.h"
+#include "projects.h"
+
+PROJ_HEAD(mbtfpq, "McBryde-Thomas Flat-Polar Quartic") "\n\tCyl, Sph";
+
+#define NITER   20
+#define EPS 1e-7
+#define ONETOL 1.000001
+#define C   1.70710678118654752440
+#define RC  0.58578643762690495119
+#define FYC 1.87475828462269495505
+#define RYC 0.53340209679417701685
+#define FXC 0.31245971410378249250
+#define RXC 3.20041258076506210122
+
+
+static XY s_forward (LP lp, PJ *P) {           /* Spheroidal, forward */
+    XY xy = {0.0,0.0};
+    double th1, c;
+    int i;
+    (void) P;
+
+    c = C * sin(lp.phi);
+    for (i = NITER; i; --i) {
+        lp.phi -= th1 = (sin(.5*lp.phi) + sin(lp.phi) - c) /
+            (.5*cos(.5*lp.phi)  + cos(lp.phi));
+        if (fabs(th1) < EPS) break;
+    }
+    xy.x = FXC * lp.lam * (1.0 + 2. * cos(lp.phi)/cos(0.5 * lp.phi));
+    xy.y = FYC * sin(0.5 * lp.phi);
+    return xy;
+}
+
+
+static LP s_inverse (XY xy, PJ *P) {           /* Spheroidal, inverse */
+    LP lp = {0.0,0.0};
+    double t;
+
+    lp.phi = RYC * xy.y;
+    if (fabs(lp.phi) > 1.) {
+        if (fabs(lp.phi) > ONETOL) {
+            proj_errno_set(P, PJD_ERR_TOLERANCE_CONDITION);
+            return lp;
+        }
+        else if (lp.phi < 0.) { t = -1.; lp.phi = -M_PI; }
+        else { t = 1.; lp.phi = M_PI; }
+    } else
+        lp.phi = 2. * asin(t = lp.phi);
+    lp.lam = RXC * xy.x / (1. + 2. * cos(lp.phi)/cos(0.5 * lp.phi));
+    lp.phi = RC * (t + sin(lp.phi));
+    if (fabs(lp.phi) > 1.)
+        if (fabs(lp.phi) > ONETOL) {
+            proj_errno_set(P, PJD_ERR_TOLERANCE_CONDITION);
+            return lp;
+        }
+        else            lp.phi = lp.phi < 0. ? -M_HALFPI : M_HALFPI;
+    else
+        lp.phi = asin(lp.phi);
+    return lp;
+}
+
+
+PJ *PROJECTION(mbtfpq) {
+
+    P->es = 0.;
+    P->inv = s_inverse;
+    P->fwd = s_forward;
+
+    return P;
+}