Merge pull request #750 from busstoptaktik/return_derivs_in_factor

make local derivatives available in PJ_FACTOR

2 files changed, 12 insertions, 3 deletions

diff --git a/src/proj.h b/src/proj.h
index 67c28b8d..0921eb51 100644
--- a/src/proj.h
+++ b/src/proj.h
@@ -167,6 +167,9 @@ struct P5_FACTORS {                  /* Common designation */
 
     double tissot_semimajor;               /* a */
     double tissot_semiminor;               /* b */
+
+    double dx_dlam, dx_dphi;
+    double dy_dlam, dy_dphi;
 };
 typedef struct P5_FACTORS PJ_FACTORS;
 
diff --git a/src/proj_4D_api.c b/src/proj_4D_api.c
index 2b250398..c91b0786 100644
--- a/src/proj_4D_api.c
+++ b/src/proj_4D_api.c
@@ -940,11 +940,11 @@ PJ_FACTORS proj_factors(PJ *P, LP lp) {
     Characteristics include meridian, parallel and areal scales, angular
     distortion, meridian/parallel, meridian convergence and scale error.
 
-    returns PJ_FACTORS. If unsuccessfull error number is set and the returned
-    struct contains NULL data.
+    returns PJ_FACTORS. If unsuccessfull, error number is set and the
+    struct returned contains NULL data.
 
 ******************************************************************************/
-    PJ_FACTORS factors = {0,0,0, 0,0,0, 0,0};
+    PJ_FACTORS factors = {0,0,0,  0,0,0,  0,0,  0,0,0,0};
     struct FACTORS f;
 
     if (0==P)
@@ -964,6 +964,12 @@ PJ_FACTORS proj_factors(PJ *P, LP lp) {
     factors.tissot_semimajor  =  f.a;
     factors.tissot_semiminor  =  f.b;
 
+    /* Raw derivatives, for completeness's sake */
+    factors.dx_dlam = f.der.x_l;
+    factors.dx_dphi = f.der.x_p;
+    factors.dy_dlam = f.der.y_l;
+    factors.dy_dphi = f.der.y_p;
+
     return factors;
 }