carla/Docs/how_to_generate_pedestrians_navigation.md

How to generate the pedestrian navigation info

### Introduction

The pedestrians to walk need information about the map in a specific format. That file that describes the map for navigation is a binary file with extension .BIN, and they are saved in the Nav folder of the map. Each map needs a .BIN file with the same name that the map, so automatically can be loaded with the map.

This .BIN file is generated from the Recast & Detour library and has all the information that allows pathfinding and crow management.

If we need to generate this .BIN file for a custom map, we need to follow this process:

• Export the map meshes
• Rebuild the .BIN file with RecastBuilder
• Copy the .BIN file in a Nav/ folder with the map

Export meshes

We have several types of meshes for navigation. The meshes need to be identified as one of those types, using specific nomenclature.

Type	Start with	Description
Ground	Road_Sidewalk	Pedestrians can walk over these meshes freely (sidewalks...).
Grass	Road_Crosswalk	Pedestrians can walk over these meshes but as a second option if no ground is found.
Road	Road_Grass	Pedestrians won't be allowed to walk on it unless we specify some percentage of pedestrians that will be allowed.
Crosswalk	Road_Road, Road_Curb, Road_Gutter or Road_Marking	Pedestrians can cross the roads only through these meshes.
Block	any other name	Pedestrians will avoid these meshes always (are obstacles like traffic lights, trees, houses...).

For instance, all road meshes need to start with Road_Road e.g: Road_Road_Mesh_1, Road_Road_Mesh_2...

This nomenclature is used by RoadRunner when it exports the map, so we are just following the same.

Also, we don't need to export meshes that are not of interest by the navigation system, like landscapes where pedestrians will not walk, or UE4's sky domes, rivers, lakes and so on. We can tag any mesh with the name NoExport and then the exporter will ignore that mesh.

Once we have all meshes with the proper nomenclature and tagged the ones that we want to ignore, we can call the Carla Exporter that is found under the File > Actors > Carla Exporter:

The .OBJ file will be saved with the name of the map with extension OBJ in the CarlaUE4/Saved folder of UE4.

Rebuild the navigation binary

With Recast & Detour library comes an executable file that needs to be used to generate the final .BIN file. The executable uses by default the parameters to work on Carla, and you only need to pass as parameter the .OBJ you exported above, and the .BIN will be created.

You can find the executable, on the Carla/Build/recast-{version}-install/bin/ folder, already compiled when Carla was installed.

Run:

$ RecastBuilder test.object

And it will create a test.bin file, that needs to be copied to the map folder, inside the Nav/ folder.

For example, this would be the structure of files of a Test map:

Test/
  ├─ Test.umap
  ├─ Nav/
  │   └─ Test.bin
  └─ OpenDrive/
      └─ Test.xodr