fix: avoid to pass non-serializable object to zmq process

On macos, there was an error when serializing the transformer arguments. Let's pass the wkt string instead and construct the transformer in the worker process.

py3dtiles/convert.py

@@ -95,7 +95,12 @@ def make_rotation_matrix(z1, z2):
 OctreeMetadata = namedtuple('OctreeMetadata', ['aabb', 'spacing', 'scale'])
 
 
-def zmq_process(activity_graph, transformer, node_store, octree_metadata, folder, write_rgb, verbosity):
+def zmq_process(activity_graph, srs_out_wkt, srs_in_wkt, node_store, octree_metadata, folder, write_rgb, verbosity):
+    transformer = None
+    if srs_out_wkt is not None:
+        crs_out = CRS(srs_out_wkt)
+        crs_in = CRS(srs_in_wkt)
+        transformer = Transformer.from_crs(crs_in, crs_out)
     context = zmq.Context()
 
     # Socket to receive messages on
@@ -371,6 +376,8 @@ def convert(files,
     rotation_matrix = None
     # srs stuff
     transformer = None
+    srs_out_wkt = None
+    srs_in_wkt = None
     if srs_out is not None:
         crs_out = CRS('epsg:{}'.format(srs_out))
         if srs_in is not None:
@@ -379,6 +386,10 @@ def convert(files,
             raise SrsInMissingException('No SRS informations in the provided files')
         else:
             crs_in = CRS(infos['srs_in'])
+
+        srs_out_wkt = crs_out.to_wkt()
+        srs_in_wkt = crs_in.to_wkt()
+
         transformer = Transformer.from_crs(crs_in, crs_out)
 
         bl = np.array(list(transformer.transform(
@@ -494,7 +505,7 @@ def add_tasks_to_process(state, name, task, point_count):
     zmq_processes = [multiprocessing.Process(
         target=zmq_process,
         args=(
-            graph, transformer, node_store, octree_metadata, outfolder, rgb, verbose)) for i in range(jobs)]
+            graph, srs_out_wkt, srs_in_wkt, node_store, octree_metadata, outfolder, rgb, verbose)) for i in range(jobs)]
 
     for p in zmq_processes:
         p.start()