1 files changed, 51 insertions, 0 deletions
diff --git a/src/projections/nell.cpp b/src/projections/nell.cpp
new file mode 100644
index 00000000..2a7ea32c
--- /dev/null
+++ b/src/projections/nell.cpp
@@ -0,0 +1,51 @@
+#define PJ_LIB__
+
+#include <math.h>
+
+#include "projects.h"
+
+PROJ_HEAD(nell, "Nell") "\n\tPCyl, Sph";
+
+#define MAX_ITER 10
+#define LOOP_TOL 1e-7
+
+
+static XY s_forward (LP lp, PJ *P) {           /* Spheroidal, forward */
+    XY xy = {0.0,0.0};
+    double k, V;
+    int i;
+    (void) P;
+
+    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;
+}
+
+
+static LP s_inverse (XY xy, PJ *P) {           /* Spheroidal, inverse */
+    LP lp = {0.0,0.0};
+    lp.lam = 2. * xy.x / (1. + cos(xy.y));
+    lp.phi = aasin(P->ctx,0.5 * (xy.y + sin(xy.y)));
+
+    return lp;
+}
+
+
+PJ *PROJECTION(nell) {
+
+    P->es = 0;
+    P->inv = s_inverse;
+    P->fwd = s_forward;
+
+    return P;
+}