Plugin / XML File Discovery

This tutorial assumes you have completed the section Installation. Let’s start with the command we ran to run the straight.xml mission:

$ cd ~/scrimmage/scrimmage
$ scrimmage ./missions/straight.xml

When executing this line, scrimmage first reads in the mission file straight.xml. This file allows for quite a few customizations such as how to visualize terrain and entities (aircraft in this case), how long we want the simulation to run, where it takes place, and quite a few other items. For our purposes though, the entity block is the one of interest. In the scenario, we have 2 teams each with fixed-wing aircraft. Thus, we have two entity blocks. The team is set with the team_id block and the entity type is set with the autonomy block. [1] When scrimmage sees the autonomy block pointing to Straight it does the following:

1. Looks for the file Straight.xml in your SCRIMMAGE_PLUGIN_PATH and loads it.

2. Looks for the params xml tag in Straight.xml.

3. It loads the custom autonomy specified by the library tag (we will discuss how to create these libraries below)

4. It saves all other items in the params block and passes these variables to the init method of the library as a map of strings pointing to strings (we will discuss this below as well).

Later tutorials will discuss how to implement custom autonomy plugins.

Finding Plugins

A command line utility called scrimmage-plugin can be used to find a plugin and print its properties. For example, to find the Straight autonomy plugin, type the following:

$ scrimmage-plugin Straight

This utility is useful for debugging file path problems.

[1]

We actually fully specify an entity with the motion_model, visual_model, controller, and autonomy. The first item concerns how a vehicle moves. In the case of a fixed-wing vehicle it can only move forward, roll, and pitch so we specify SimpleAircraft as the motion model. Quadrotors have more degrees of freedom so they have the SimpleQuadrotor motion model. As the names imply, there are higher fidelity motion models available.