[Proj] patch to PJ_hammer.c for inverse projection

[Jeff Whitaker]

Here's a patch against SVN head to PJ_hammer.c that implements the 
inverse projection for Hammer and Eckert-Greifendorff (based on 
http://mathworld.wolfram.com/Hammer-AitoffEqual-AreaProjection.html):

Index: PJ_hammer.c
===================================================================
--- PJ_hammer.c (revision 1954)
+++ PJ_hammer.c (working copy)
@@ -4,7 +4,7 @@
  #define PJ_LIB__
  # include      <projects.h>
  PROJ_HEAD(hammer, "Hammer & Eckert-Greifendorff")
-       "\n\tMisc Sph, no inv.\n\tW= M=";
+       "\n\tMisc Sph, \n\tW= M=";
  FORWARD(s_forward); /* spheroid */
         double cosphi, d;

@@ -13,6 +13,13 @@
         xy.y = P->rm * d * sin(lp.phi);
         return (xy);
  }
+INVERSE(s_inverse); /* spheroid */
+       double z;
+       z = sqrt(1.-0.25*P->w*P->w*xy.x*xy.x-0.25*xy.y*xy.y);
+       lp.lam = aatan2(P->w * xy.x * z,2. * z * z - 1)/P->w;
+       lp.phi = aasin(z * xy.y);
+       return (lp);
+}
  FREEUP; if (P) pj_dalloc(P); }
  ENTRY0(hammer)
         if (pj_param(P->ctx, P->params, "tW").i) {
@@ -25,5 +32,5 @@
                 P->m = 1.;
         P->rm = 1. / P->m;
         P->m /= P->w;
-       P->es = 0.; P->fwd = s_forward;
+       P->es = 0.; P->fwd = s_forward; P->inv = s_inverse;
  ENDENTRY(P)


-Jeff
-- 
Jeffrey S. Whitaker         Phone  : (303)497-6313
Meteorologist               FAX    : (303)497-6449
NOAA/OAR/PSD  R/PSD1        Email  : Jeffrey.S.Whitaker at noaa.gov
325 Broadway                Office : Skaggs Research Cntr 1D-113
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