making_terrain_lidar.md

How to make your own terrain

You should not need to create your own terrain for this project, so this section will be brief and provide more for debugging purposes.

• 1. Terrain
  • 1.1. Create a terrain based on a heightmap
  • 1.2. Create a terrain based on real world terrain
• 2. LiDAR

1. Terrain

1.1. Create a terrain based on a heightmap

This video shows the steps.

In summary:

1. Create a .png in your favorite graphical editing software.
   • Make sure to remove the alpha channel
   • Make sure that the image is unsigned 8-bit
   • Make sure that the image is square
   • Make sure that the number of pixels per edge is $2^n+1$, where $n=0,1,2,3...$
   • White marks the tallest areas and black marks the shortest areas of your terrain
2. Add the .png you created to the .world file for your new terrain.
   • The <size> tag specifies how large your terrain actually is in simulation (x, y, z in meters)
3. Modify cmake/sitl_target.cmake with the name of your world
4. Add your terrain files to the lm_setup.sh script to place them in right places or do so manually

1.2. Create a terrain based on real world terrain

Summary of Gazebo DEMs Tutorial:

1. Follow the steps below to create a terrain and world.

   # Install dependencies for manipulating terrain data
   sudo apt-get install gdal-bin libgdal-dev
   pip3 install GDAL
   
   # Make and step into gazebo resources directory
   mkdir -p /tmp/gazebo
   cd /tmp/gazebo
   
   # Get terrain file and unzip
   wget https://github.com/osrf/gazebo_tutorials/raw/master/dem/files/mtsthelens_after.zip
   unzip ./mtsthelens_after.zip -d .
   
   # Rename file to something friendly
   mv ./10.2.1.1043901.dem ./mtsthelens.dem
   
   # Make a directory to store dem files
   mkdir -p media/dem
   
   # Downsample the terrain file and make sure it is the right format at the output
   gdalwarp -ts 129 129 /tmp/gazebo/mtsthelens.dem /tmp/gazebo/media/dem/mtsthelens_129.tiff
   gdal_translate -of USGSDEM /tmp/gazebo/media/dem/mtsthelens_129.tiff /tmp/gazebo/media/dem/mtsthelens_129.dem
   
   # Remove temporary files
   rm -f /tmp/gazebo/media/dem/mtsthelens_129.tiff /tmp/gazebo/media/dem/mtsthelens_129.dem.aux.xml /tmp/gazebo/mtsthelens.dem /tmp/gazebo/mtsthelens_after.zip
   
   # Get the world definition for the terrain
   wget https://github.com/osrf/gazebo_tutorials/raw/master/dem/files/volcano.world
   
   # Tell Gazebo where to look for the terrain file and launch to double check that it worked
   # Be sure of sourcing gazebo setup.sh in your own installation path
   source /usr/share/gazebo/setup.sh
   GAZEBO_RESOURCE_PATH="$GAZEBO_RESOURCE_PATH:/tmp/gazebo" gazebo /tmp/gazebo/volcano.world

2. Follow steps 2-4 from above.

2. LiDAR

This entails a somewhat involved process consisting of

1. Creating a sensor model in .sdf format for the lidar similar to what is done for the lmlidar.
2. Creating a vehicle model in .sdf format to include that lidar, even if that vehicle already exists in other iterations. An example of this is the iris_lmlidar vehicle model.
3. Creating a ROMFS script formatted as <number>_vehicle_name. E.g. 1043_iris_lmlidar.
4. Updating line 94 of the cmake file with the name of your vehicle (specifically the one that includes your new lidar).
5. Updating the setup script to copy your new models and ROMFS script into the right places in Gazebo and PX4.