03. Map Setup

Map Setup

Great! We have our simulation environment ready now. However, we cannot localize the robot just yet. The poor robot has zero information on its surroundings! Let us generate a map for it so that it knows what to expect in this environment.

Generally speaking, in the development of a robotic project, engineers utilize Mapping tools to measure and map the area robot will be operating in. Since we are developing in simulation environment the problem is simplified. We could generate the map from Gazebo world directly using a ROS package: pgm_map_creator .

Note that currently, the map creator could not handle objects in the environment well. Please use the it with vertical surfaces only!

Udacity Office Space Map

Udacity Office Space Map

PGM Map File

The map ROS AMCL Package uses is a pgm file. A pgm file is a grayscale image file. For more information about pgm file or more generally, pnm file, please refer to Netpbm format Wiki Page .

By default, AMCL package will treat 'darker' pixels as obstacle in the pgm map file, and 'lighter' pixels as free space. The threshold could be set as a parameter which we will cover when we are building the launch file.

Navigate to your ROS package folder and create a maps folder. That's where your map file will reside. 

$ cd /home/workspace/catkin_ws/src/<YOUR PACKAGE NAME>
$ mkdir maps

PGM Map Creator

Install Dependencies

We need libignition-math2-dev and protobuf-compiler to compile the map creator: 

sudo apt-get install libignition-math2-dev protobuf-compiler

Clone the Repository

Clone the package pgm_map_creator to your src folder. 

cd /home/workspace/catkin_ws/src/
git clone https://github.com/udacity/pgm_map_creator.git

Build the package: 

cd ..
catkin_make

Add and Edit the World File

Copy the Gazebo world you created to the world folder 

cp <YOUR GAZEBO WORLD FILE> src/pgm_map_creator/world/<YOUR GAZEBO WORLD FILE>

Insert the map creator plugin to your map file. Open the map file using the editor of your choice. Add the following tag towards the end of the file, but just before </world> tag: 

<plugin filename="libcollision_map_creator.so" name="collision_map_creator"/>

Create the PGM Map!

Open a terminal, run gzerver with the map file: 

gzserver src/pgm_map_creator/world/<YOUR GAZEBO WORLD FILE>

Open another terminal, launch the request_publisher node 

roslaunch pgm_map_creator request_publisher.launch

Wait for the plugin to generate map. It will be located in the map folder of the pgm_map_creator ! Open it to do a quick check of the map. If the map is cropped, you might want to adjust the parameters in launch/request_publisher.launch , namely the x and y values, which defines the size of the map: 

  <arg name="xmin" default="-15" />
  <arg name="xmax" default="15" />
  <arg name="ymin" default="-15" />
  <arg name="ymax" default="15" />
  <arg name="scan_height" default="5" />
  <arg name="resolution" default="0.01" />

Edit the Map

Remember, the map is an image, which means you could edit it using image processing softwares like gimp in Linux. If you have found the map not accurate due to the models, feel free to edit the pgm file directly!

Add the Map to Your Package

Now we have the map file, let us move it to where it is needed! That is the maps folder you created at the very beginning. 

cd /home/workspace/catkin_ws/
cp src/pgm_map_creator/maps/<YOUR MAP NAME>  src/<YOUR PACKAGE NAME>/maps/<YOUR MAP NAME>

You would also need a yaml file providing the metadata about the map . Create a yaml file next to your map: 

cd src/<YOUR PACKAGE NAME>/src/maps
touch <YOUR MAP NAME>.yaml

Open the yaml file and add the following lines to it: 

image: <YOUR MAP NAME>
resolution: 0.01
origin: [-15.0, -15.0, 0.0]
occupied_thresh: 0.65
free_thresh: 0.196
negate: 0

Note that the origin of the map should correspond to your map's size. For example, the default map size is 30 by 30, so the origin will be [-15, -15, 0], i.e. half the size of the map.

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