refactor: RootMaterialDecorator as default for the ODD (#3415)

`getOpenDataDetector()` gives by default the `JsonMaterialDecorator`, which does not give good results (at least in my use cases), and for most usecases, we anyways give directly the Root based one.

Examples/Python/python/acts/examples/odd.py

@@ -20,6 +20,13 @@ def getOpenDataDetector(
     odd_dir: Optional[Path] = None,
     logLevel=acts.logging.INFO,
 ):
+    """This function sets up the open data detector. Requires DD4hep.
+    Parameters
+    ----------
+    mdecorator: Material Decorator, take RootMaterialDecorator if non is given
+    odd_dir: if not given, try to get via ODD_PATH environment variable
+    logLevel: logging level
+    """
     import acts.examples.dd4hep
 
     customLogLevel = acts.examples.defaultLogging(logLevel=logLevel)
@@ -86,11 +93,9 @@ def geoid_hook(geoid, surface):
     )
     detector = acts.examples.dd4hep.DD4hepDetector()
 
-    config = acts.MaterialMapJsonConverter.Config()
     if mdecorator is None:
-        mdecorator = acts.JsonMaterialDecorator(
-            rConfig=config,
-            jFileName=str(odd_dir / "config/odd-material-mapping-config.json"),
+        mdecorator = acts.examples.RootMaterialDecorator(
+            fileName=str(odd_dir / "data/odd-material-maps.root"),
             level=customLogLevel(minLevel=acts.logging.WARNING),
         )
 

Examples/Python/tests/test_examples.py

@@ -28,7 +28,7 @@
     GenericDetector,
     AlignedDetector,
 )
-from acts.examples.odd import getOpenDataDetector
+from acts.examples.odd import getOpenDataDetector, getOpenDataDetectorDirectory
 
 
 u = acts.UnitConstants
@@ -678,7 +678,14 @@ def test_material_mapping(material_recording, tmp_path, assert_root_hash):
 
     s = Sequencer(numThreads=1)
 
-    detector, trackingGeometry, decorators = getOpenDataDetector()
+    odd_dir = getOpenDataDetectorDirectory()
+    config = acts.MaterialMapJsonConverter.Config()
+    mdecorator = acts.JsonMaterialDecorator(
+        level=acts.logging.INFO,
+        rConfig=config,
+        jFileName=str(odd_dir / "config/odd-material-mapping-config.json"),
+    )
+    detector, trackingGeometry, decorators = getOpenDataDetector(mdecorator)
 
     from material_mapping import runMaterialMapping