This feature allows users to ingest any OpenDRIVE file as a CARLA map out-of-the-box. In order to do so, the simulator will automatically generate a road mesh for actors to navigate through.
This mode runs a full simulation using only an OpenDRIVE file, without the need of any additional gemotires or assets. To this end, the simulator takes an OpenDRIVE file and procedurally creates a temporal 3D mesh to run the simulation with.
The resulting mesh describes the road definition in a minimalistic manner. All the elements will correspond with the OpenDRIVE file, but besides that, there will be only void. In order to prevent vehicles from falling off the road, two measures have been taken.
Traffic lights, stops and yields will be generated on the fly, as happens when using any map. Pedestrians will navigate over the sidewalks and crosswalks that appear in the map. All of these elements, and every detail on the road, are based on the OpenDRIVE file. As the standalone mode uses the `.xodr` directly, any issues in it will propagate to the simulation. This could be an issue especially at junctions, where many lanes are mixed.
* The sidewalks height is currently hardcoded. This ensures collisions with them are detected even if the map definition does not include this field ??
In order to open an OpenDRIVE file, the Python API includes now the method [`client.generate_opendrive_world()`](python_api.md#carla.Client.generate_opendrive_world). This will block the simulation until the new one is ready. The method needs for two parameters.
*__`opendrive`__ is the content of the OpenDRIVE file parsed as a string.
*__`parameters`__ is a [carla.OpendriveGenerationParameters](python_api.md#carla.OpendriveGenerationParameters) containing settings for the generation of the mesh.
*__`vertex_distance`__ is the distance between the vertices of the mesh. The bigger, the distance, the more inaccurate the mesh will be. However, if the distance is too small, the resulting mesh will be too heavy to work with.
*__`max_road_length`__ is the maximum length of a portion of the mesh. The mesh is divide in portions to reduce rendering overhead. If a portion is not visible, UE will not render it. The smaller the portions, the more probably they are discarded. However, if the portions are too small, UE will have too many objects to manage, and performance will be affected too.
*__`wall_height`__ states the height of the additional walls created on the boundaries of the road. These prevent vehicles from falling to the void.
*__`additional_width`__ is an small width increment applied to the junction lanes. This is a safety measure to prevent vehicles from falling.
*__`smooth_junctions`__ if __True__, some information of the OpenDRIVE will be reinterpreted to smooth the final mesh at junctions. This is done to prevent some inaccuracies that may occur when various lanes meet. If set to __False__, the mesh will be generated exactly as described in the OpenDRIVE.
*__`enable_mesh_visibility`__ if __False__, the mesh will not be rendered, which could save a lot of work to the simulator.
In order to easily test this feature, the `config.py` script in `PythonAPI/util/` has a new argument, `-x` or `--xodr-path`. This argument contains a string with the path to the `.xodr` file. If the mesh is generated with this script, the parameters used will always be the default ones.
__[carla.OpendriveGenerationParameters](python_api.md#carla.OpendriveGenerationParameters)__ uses __content of the OpenDRIVE file parsed as string__. On the contrary, __`config.py`__ script needs __the path to the `.xodr` file__.
The generation of the mesh is the key element of this mode. The feature can only be successful if the resulting mesh is smooth and fits its definition perfectly. For that reason, this step is constantly being improved. In the last iterations, junctions have been polished to avoid inaccuracies that occur, especially where uneven lanes joined.
Besides that, instead of creating the whole map as a unique mesh, different fragments are created. Working smaller prevents unexpected issues. Also, by dividing the mesh, not all of it has to be rendered at a time. This is a step towards a larger goal, where the feature will be able to generate huge maps.
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That covers all there is to know so far, regarding the OpenDRIVE standalone mode. Take the chance and use any OpenDRIVE map to test it in CARLA.
Doubts and suggestions in the forum.
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