Merge pull request #329 from jswhit/master

inverse for hammer projection

4 files changed, 43 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index dfa67267..ece889c4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,6 @@
+2015-12-13: jswhit <https://github.com/jswhit>
+	* : Add inverse hammer transform (pull request #329).
+
 2015-09-10 sisyphus <https://github.com/sisyphus>
 	* : Rename PVALUE in pj_param.cto prevent Windows variable name clash
 
diff --git a/nad/testvarious b/nad/testvarious
index 4f3ca324..972dc222 100755
--- a/nad/testvarious
+++ b/nad/testvarious
@@ -266,6 +266,22 @@ $EXE +proj=robin +datum=WGS84 \
 1741397.30      4276351.58 0.00
 EOF
 echo "##############################################################" >> ${OUT}
+echo "Test hammer projection (pull request #329)" >> ${OUT}
+$EXE +proj=latlong +datum=WGS84 \
+ +to +proj=hammer  +datum=WGS84 \
+ -E >>${OUT} <<EOF
+-30 40
+-35 45
+20 40
+EOF
+$EXE +proj=hammer  +datum=WGS84 \
+ +to +proj=latlong +datum=WGS84 \
+ -E >>${OUT} <<EOF
+-2711575.08	4395506.62 0.00
+-2964412.70	4929091.33 0.00
+1811748.54	4377349.50 0.00
+EOF
+echo "##############################################################" >> ${OUT}
 echo "Test healpix forward projection on sphere" >> ${OUT}
 $EXE +proj=latlong +a=1 +lon_0=0 \
  +to +proj=healpix +a=1 +lon_0=0  -f '%.'5'f' \
diff --git a/nad/tv_out.dist b/nad/tv_out.dist
index f3c6c39f..e58f6da1 100644
--- a/nad/tv_out.dist
+++ b/nad/tv_out.dist
@@ -92,6 +92,14 @@ Test robinson projection (#113)
 -2963455.42     4805073.65 0.00	35dW	45dN 0.000
 1741397.30      4276351.58 0.00	20d0'0.002"E	40d0'0.066"N 0.000
 ##############################################################
+Test hammer projection (pull request #329)
+-30 40	-2711575.08	4395506.62 0.00
+-35 45	-2964412.70	4929091.33 0.00
+20 40	1811748.54	4377349.50 0.00
+-2711575.08	4395506.62 0.00	30dW	40dN 0.000
+-2964412.70	4929091.33 0.00	35dW	45dN 0.000
+1811748.54	4377349.50 0.00	20dE	40dN 0.000
+##############################################################
 Test healpix forward projection on sphere
 0 41.81031	0.00000	0.78540 0.00000
 -90 0	-1.57080	0.00000 0.00000
diff --git a/src/PJ_hammer.c b/src/PJ_hammer.c
index 719a2ce4..31e7a127 100644
--- a/src/PJ_hammer.c
+++ b/src/PJ_hammer.c
@@ -2,9 +2,10 @@
 	double w; \
 	double m, rm;
 #define PJ_LIB__
+#define EPS 1.0e-10
 # 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 +14,19 @@ FORWARD(s_forward); /* spheroid */
 	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);
+	if (fabs(2.*z*z-1.) < EPS) {
+		lp.lam = HUGE_VAL;
+		lp.phi = HUGE_VAL;
+		pj_errno = -14;
+	} else {
+		lp.lam = aatan2(P->w * xy.x * z,2. * z * z - 1)/P->w;
+		lp.phi = aasin(P->ctx,z * xy.y);
+	}
+	return (lp);
+}
 FREEUP; if (P) pj_dalloc(P); }
 ENTRY0(hammer)
 	if (pj_param(P->ctx, P->params, "tW").i) {
@@ -25,5 +39,5 @@ ENTRY0(hammer)
 		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)