Reverse direction of deformation operations/transformations/deformation

Changed the direction of dt-calculation to follow the same convention as
helmert. Changed from dt = t_c - t_obs to dt = t_obs - t_c, which
effectively reverses the direction of the operation. Existing projstrings
using deformation can simply reverse the direction of the operation to
achieve the same results as before this commit.

1 files changed, 6 insertions, 6 deletions

diff --git a/src/transformations/deformation.cpp b/src/transformations/deformation.cpp
index 9221d39e..14f34e4e 100644
--- a/src/transformations/deformation.cpp
+++ b/src/transformations/deformation.cpp
@@ -172,7 +172,7 @@ static PJ_XYZ forward_3d(PJ_LPZ lpz, PJ *P) {
     out = in;
 
     if (Q->t_obs != HUGE_VAL) {
-        dt = Q->t_epoch - Q->t_obs;
+        dt = Q->t_obs - Q->t_epoch;
     } else {
         out = proj_coord_error(); /* in the 3D case +t_obs must be specified */
         proj_log_debug(P, "deformation: +t_obs must be specified");
@@ -196,9 +196,9 @@ static PJ_COORD forward_4d(PJ_COORD in, PJ *P) {
     PJ_COORD out = in;
 
     if (Q->t_obs != HUGE_VAL) {
-            dt = Q->t_epoch - Q->t_obs;
+            dt = Q->t_obs - Q->t_epoch;
         } else {
-            dt = Q->t_epoch - in.xyzt.t;
+            dt = in.xyzt.t - Q->t_epoch ;
     }
 
     shift = get_grid_shift(P, in.xyz);
@@ -219,7 +219,7 @@ static PJ_LPZ reverse_3d(PJ_XYZ in, PJ *P) {
     out.xyz = in;
 
     if (Q->t_obs != HUGE_VAL) {
-        dt = Q->t_epoch - Q->t_obs;
+        dt = Q->t_obs - Q->t_epoch;
     } else {
         out = proj_coord_error(); /* in the 3D case +t_obs must be specified */
         proj_log_debug(P, "deformation: +t_obs must be specified");
@@ -238,9 +238,9 @@ static PJ_COORD reverse_4d(PJ_COORD in, PJ *P) {
 
 
     if (Q->t_obs != HUGE_VAL) {
-            dt = Q->t_epoch - Q->t_obs;
+            dt = Q->t_obs - Q->t_epoch;
         } else {
-            dt = Q->t_epoch - in.xyzt.t;
+            dt = in.xyzt.t - Q->t_epoch;
     }
 
     out.xyz = reverse_shift(P, in.xyz, dt);