Fix proj_assign_context()/pj_set_ctx() with pipelines and alternative coord operations

Fixes https://github.com/OSGeo/gdal/issues/1989

pj_set_ctx() only changes the context to the main object. It should also
recurse down to the steps of the pipeline and the alternative coordinate
operations hold in alternativeCoordinateOperations

In the GDAL use case with multithreaded reprojection, and objects being transferred
between thread, this would cause a failed coordinate transformation to affect
an unrelated transformation of another thread...

1 files changed, 8 insertions, 0 deletions

diff --git a/src/ctx.cpp b/src/ctx.cpp
index 622a814d..bcb6e1cc 100644
--- a/src/ctx.cpp
+++ b/src/ctx.cpp
@@ -60,6 +60,14 @@ void pj_set_ctx( projPJ pj, projCtx ctx )
     if (pj==nullptr)
         return;
     pj->ctx = ctx;
+    if( pj->is_pipeline )
+    {
+        pj_pipeline_assign_context_to_steps(pj, ctx);
+    }
+    for( const auto &alt: pj->alternativeCoordinateOperations )
+    {
+        pj_set_ctx(alt.pj, ctx);
+    }
 }
 
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