Fixes visualization markers to hide them from camera renderings (#103)

# Description

Previously, the visualization markers would get rendered in the camera
images. However, this is often undesirable since the markers are only
used for debug visualizations. This behavior turns these off by default.

## Type of change

- New feature (non-breaking change which adds functionality)
- This change requires a documentation update

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [x] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file

source/extensions/omni.isaac.orbit/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.8.4"
+version = "0.8.5"
 
 # Description
 title = "ORBIT framework for Robot Learning"

source/extensions/omni.isaac.orbit/docs/CHANGELOG.rst

 Changelog
 ---------
 
+0.8.5 (2023-08-03)
+~~~~~~~~~~~~~~~~~~
+
+Fixed
+^^^^^
+
+* Fixed the :class:`omni.isaac.orbit.markers.Visualizationmarkers` class so that the markers are not visible in camera rendering mode.
+
+Changed
+^^^^^^^
+
+* Simplified the creation of the point instancer in the :class:`omni.isaac.orbit.markers.Visualizationmarkers` class. It now creates a new
+  prim at the next available prim path if a prim already exists at the given path.
+
+
 0.8.4 (2023-08-02)
 ~~~~~~~~~~~~~~~~~~
 

source/extensions/omni.isaac.orbit/omni/isaac/orbit/markers/visualization_markers.py

@@ -22,9 +22,11 @@ from dataclasses import MISSING
 from typing import Any, Dict, List, Optional, Union
 
 import omni.isaac.core.utils.prims as prim_utils
+import omni.isaac.core.utils.stage as stage_utils
+import omni.kit.commands
 from omni.isaac.core.materials import PreviewSurface
 from omni.isaac.core.prims import GeometryPrim
-from pxr import Gf, UsdGeom, Vt
+from pxr import Gf, Sdf, UsdGeom, Vt
 
 from omni.isaac.orbit.utils.assets import check_file_path
 from omni.isaac.orbit.utils.configclass import configclass
@@ -162,21 +164,13 @@ class VisualizationMarkers:
             cfg (VisualizationMarkersCfg): The configuration for the markers.
 
         Raises:
-            ValueError: When a prim already exists at the :obj:`prim_path` and it is not a :class:`UsdGeom.PointInstancer`.
             ValueError: When no markers are provided in the :obj:`cfg`.
         """
-        # resolve default markers in the UI elements
-        # -- prim path
-        if prim_utils.is_prim_path_valid(prim_path):
-            # retrieve prim if it exists
-            prim = prim_utils.get_prim_at_path(prim_path)
-            if not prim.IsA(UsdGeom.PointInstancer):
-                raise ValueError(f"The prim at path {prim_path} cannot be parsed as a `UsdGeom.PointInstancer` object.")
-            self._instancer_manager = UsdGeom.PointInstancer(prim)
-        else:
-            # create a new prim
-            prim = prim_utils.define_prim(prim_path, "PointInstancer")
-            self._instancer_manager = UsdGeom.PointInstancer(prim)
+        # get next free path for the prim
+        prim_path = stage_utils.get_next_free_path(prim_path)
+        # create a new prim
+        prim = prim_utils.define_prim(prim_path, "PointInstancer")
+        self._instancer_manager = UsdGeom.PointInstancer(prim)
         # store inputs
         self.prim_path = prim_path
         self.cfg = cfg
@@ -409,6 +403,14 @@ class VisualizationMarkers:
                 scale=cfg.scale,
                 attributes=cfg.attributes,
             )
+            # make marker invisible to secondary rays
+            omni.kit.commands.execute(
+                "ChangePropertyCommand",
+                prop_path=Sdf.Path(f"{marker_prim_path}.primvars:invisibleToSecondaryRays"),
+                value=True,
+                prev=None,
+                type_to_create_if_not_exist=Sdf.ValueTypeNames.Bool,
+            )
             # set visibility
             prim_utils.set_prim_visibility(prim, visible=cfg.visible)
             # create color attribute