1 files changed, 31 insertions, 9 deletions

diff --git a/src/transformations/hgridshift.cpp b/src/transformations/hgridshift.cpp
index e9983df6..3b6e366f 100644
--- a/src/transformations/hgridshift.cpp
+++ b/src/transformations/hgridshift.cpp
@@ -17,6 +17,7 @@ struct hgridshiftData {
     double t_final = 0;
     double t_epoch = 0;
     ListOfHGrids grids{};
+    bool defer_grid_opening = false;
 };
 } // anonymous namespace
 
@@ -25,6 +26,14 @@ static PJ_XYZ forward_3d(PJ_LPZ lpz, PJ *P) {
     PJ_COORD point = {{0,0,0,0}};
     point.lpz = lpz;
 
+    if ( Q->defer_grid_opening ) {
+        Q->defer_grid_opening = false;
+        Q->grids = proj_hgrid_init(P, "grids");
+        if ( proj_errno(P) ) {
+            return proj_coord_error().xyz;
+        }
+    }
+
     if (!Q->grids.empty()) {
         /* Only try the gridshift if at least one grid is loaded,
          * otherwise just pass the coordinate through unchanged. */
@@ -40,6 +49,14 @@ static PJ_LPZ reverse_3d(PJ_XYZ xyz, PJ *P) {
     PJ_COORD point = {{0,0,0,0}};
     point.xyz = xyz;
 
+    if ( Q->defer_grid_opening ) {
+        Q->defer_grid_opening = false;
+        Q->grids = proj_hgrid_init(P, "grids");
+        if ( proj_errno(P) ) {
+            return proj_coord_error().lpz;
+        }
+    }
+
     if (!Q->grids.empty()) {
         /* Only try the gridshift if at least one grid is loaded,
          * otherwise just pass the coordinate through unchanged. */
@@ -114,9 +131,9 @@ PJ *TRANSFORMATION(hgridshift,0) {
         return destructor (P, PJD_ERR_NO_ARGS);
     }
 
-   /* TODO: Refactor into shared function that can be used  */
-   /*       by both vgridshift and hgridshift               */
-   if (pj_param(P->ctx, P->params, "tt_final").i) {
+    /* TODO: Refactor into shared function that can be used  */
+    /*       by both vgridshift and hgridshift               */
+    if (pj_param(P->ctx, P->params, "tt_final").i) {
         Q->t_final = pj_param (P->ctx, P->params, "dt_final").f;
         if (Q->t_final == 0) {
             /* a number wasn't passed to +t_final, let's see if it was "now" */
@@ -131,16 +148,21 @@ PJ *TRANSFORMATION(hgridshift,0) {
         }
     }
 
-   if (pj_param(P->ctx, P->params, "tt_epoch").i)
+    if (pj_param(P->ctx, P->params, "tt_epoch").i)
         Q->t_epoch = pj_param (P->ctx, P->params, "dt_epoch").f;
 
 
-    Q->grids = proj_hgrid_init(P, "grids");
-    /* Was gridlist compiled properly? */
-    if ( proj_errno(P) ) {
-        proj_log_error(P, "hgridshift: could not find required grid(s).");
-        return destructor(P, PJD_ERR_FAILED_TO_LOAD_GRID);
+    if( P->ctx->defer_grid_opening ) {
+        Q->defer_grid_opening = true;
     }
+    else {
+        Q->grids = proj_hgrid_init(P, "grids");
+        /* Was gridlist compiled properly? */
+        if ( proj_errno(P) ) {
+            proj_log_error(P, "hgridshift: could not find required grid(s).");
+            return destructor(P, PJD_ERR_FAILED_TO_LOAD_GRID);
+        }
+     }
 
     return P;
 }