proj_create_crs_to_crs(): fix when there are only transformations with ballpark steps

Currently we would discard all operations, resulting in a PJ object with
zero candidates. Better use those operations if nothing better is available.

Was seen on transforming from ETRS89 / UTM zone 31N + EGM96 height to WGS 84 (G1762).
The horizontal transformation from ETRS89 to WGS 84 (G1762) is a ballpark one.

1 files changed, 18 insertions, 3 deletions

diff --git a/src/4D_api.cpp b/src/4D_api.cpp
index 70eaac6a..40cd609f 100644
--- a/src/4D_api.cpp
+++ b/src/4D_api.cpp
@@ -1137,6 +1137,8 @@ PJ  *proj_create_crs_to_crs_from_pj (PJ_CONTEXT *ctx, const PJ *source_crs, cons
 
     try
     {
+        bool skipDefaultTransforms = true;
+
         // Iterate over source->target candidate transformations and reproject
         // their long-lat bounding box into the source CRS.
         for( int i = 0; i < op_count; i++ )
@@ -1149,12 +1151,25 @@ PJ  *proj_create_crs_to_crs_from_pj (PJ_CONTEXT *ctx, const PJ *source_crs, cons
             double north_lat = 0.0;
 
             const char* name = proj_get_name(op);
-            if( name && (strstr(name, "Ballpark geographic offset") ||
+            bool canUseOp = true;
+            if( skipDefaultTransforms &&
+                name && (strstr(name, "Ballpark geographic offset") ||
                          strstr(name, "Ballpark geocentric translation")) )
             {
-                // Skip default transformations
+                // Skip default transformations unless there is already one at
+                // the beginning (in which case all of them will have one)
+                if( i == 0 )
+                {
+                    skipDefaultTransforms = false;
+                }
+                else
+                {
+                    canUseOp = false;
+                }
             }
-            else if( proj_get_area_of_use(ctx, op,
+
+            if( canUseOp &&
+                proj_get_area_of_use(ctx, op,
                         &west_lon, &south_lat, &east_lon, &north_lat, nullptr) )
             {
                 if( west_lon <= east_lon )