Populate the scene with actors

About Actor Movement System

Actor Movement System, aka AMS, is an Unreal Engine plugin made by Parrot. It allows the end-user to put one or more moving targets into the scene and make them move along a given path.

These moving targets can be of several shapes. So far, human pedestrians and vehicles are supported.

Some UE4 applications coming with Parrot Sphinx include one or several “paths”. For these apps, there is systematically a path called DefaultPath. By default, they are visible at run-time with Unreal cameras.

The control of the plugin is done through the application’s command line. The next sections describe the available parameters to pass.

List available actors

The command -list-actors shows the available pedestrians and vehicles that can be used. They are common for all UE4 applications.

$ parrot-ue4-empty -list-actors
== Available Characters ======================================
- Malcolm
- Stefani
- Jasper
==============================================================
== Available Vehicles ========================================
- Hatchback
- SUV
- Pickup
- SportsCar
- BoxTruck
==============================================================

List available paths

The command -list-paths shows the different paths predefined in a given world level.

$ parrot-ue4-forest -level=main -list-paths
== Available Paths ===========================================
Path name : DefaultPath
==============================================================

Spawn actors

The option -ams-path= tells the plugin to spawn N moving targets along the path called PathName. You can append several of this option in the same command line.

It is formatted as follows:

-ams-path=<PathName>,<Actor1[:<drone>]>[,<Actor2>,...]

Note

Once spawned, actors are automatically put in pause. To make them move, set the Web dashboard parameter pause to false. Here’s the command line to do that:

$ sphinx-cli param -m world actors pause false

When several actors are set in the same path, they will be spawned evenly all along the path so that the risk of collision gets reduced. That being said, if the actors do not have the same speed, collisions are likely to happen.

To have one actor being tracked by a drone, you need to append “:<drone_name>” after the name of the actor. The wildcard ‘*’ can be used if you do not want to bother with giving the right drone name. In that case, the first drone found in the simulation will be taken. Once an actor is tracked, its GPS and barometer information will be injected to the drone firmware at the place of the drone controller’s.

Example:

$ parrot-ue4-empty -ams-path=DefaultPath,Pickup:* -ams-path=RunPath,Jasper

Note

It is not possible to assign a given drone to several actors at the same time. As a consequence, the wildcard ‘*’ should be used only once in the command line.

The tracked actor always has a red marker above itself. The markers are kept invisible for all cameras belonging to the simulated drone.

If you want to spawn pedestrians and vehicles on the same path, pedestrians would be spawned before vehicles even if you write the vehicles names at first in the command line. This order was chosen to avoid any unwanted collision between a vehicle and a pedestrian because of their different speed.

For example:

$ parrot-ue4-empty -ams-path=DefaultPath,Pickup,SUV,Jasper,Malcolm

List available actor-related spawn points

The command -list-actor-spawn-points shows the available spawn points to get the drone on a vehicle or next to a pedestrian. Note: to have this command be working, the command line must contain the actor(s) you want to spawn alongside -list-actor-spawn-points.

Command line example:

$ parrot-ue4-empty -ams-path=DefaultPath,Pickup,SUV -list-actor-spawn-points
== Available Spawn Points for vehicles ====================================
- Name: SUV
  Pose: 3.515376 3.436066 2.300000 0.000000 0.000000 -47.455574
- Name: Pickup
  Pose: 0.565791 1.548941 1.300000 0.000000 0.000000 140.429077
== Available Spawn Points for characters ==================================
==============================================================

Take off from vehicle using AMS

First you need to spawn a vehicle using AMS then you need to specify the name of that vehicle using the command line argument ::pose=

Command line example:

$ sphinx <my.drone>::pose="pickup" & parrot-ue4-empty -ams-path=DefaultPath,Pickup

Spawn drone near pedestrians

First you need to spawn a pedestrian using AMS then you need to specify his name using the command line argument ::pose=, same thing as vehicles. The drone are spawned 1 meter behind the selected pedestrian.

Command line example:

$ sphinx <my.drone>::pose="Jasper" & parrot-ue4-empty -ams-path=DefaultPath,Jasper

Attaching tags to vehicles

Vehicles can have a visual tag placed on their roof. Once you spawn one or several vehicles, you can set the same tag to all of them using the web dashboard (or sphinx-cli). The parameter tags_name takes the name of the desired texture. The list of available textures is below.

• aruco

• parrot_logo

• h_boost

• h_logo

• rotational_invariant_dil

• white_logo

• empty string will hide the tag

• wrong name will hide the tag with an error

Here’s a command line example to set the tags_name parameter:

$ sphinx-cli param -m world actors tags_name parrot_logo

The parameter tags_material takes the name of the desired material to use with the tag. The list of available materials is below.

• Default

• NoReflections

Wrong material name will display an error in the terminal. Here’s a command line example to set the tags_material parameter:

$ sphinx-cli param -m world actors tags_material NoReflections

By default, all tags have the dimension of a paper sheet. However, these dimensions can be changed by setting the parameters tags_width and tags_height using the Web dashboard or sphinx-cli. Note: values are expressed in cm.

Here’s a command line example :

$ sphinx-cli param -m world actors tags_width 40
$ sphinx-cli param -m world actors tags_height 30

The parameters tags_offset_x, tags_offset_y and tags_offset_z add offsets to the tag’s location in its local reference frame. Note: Values are expressed in cm.

Here’s a command line example to shift the position of the current tag:

$ sphinx-cli param -m world actors tags_offset_x 5
$ sphinx-cli param -m world actors tags_offset_y 10
$ sphinx-cli param -m world actors tags_offset_z 20

Note

Changing the tag’s location by editing the parameter tags_location resets all offsets.

Lift actor’s hand

In addition of standing, walking and running, a pedestrian can lift his right hand to a 90° angle.

First you need to spawn a pedestrian using AMS. Then using the web dashboard (or sphinx-cli), you can set the parameter lift_hand to raise/lower the actor’s arm.

Note

The pedestrian must be paused to be able to lift his hand.

Here’s a command line example to set the lift_hand parameter:

$ sphinx-cli param -m world actors lift_hand true

It’s also possible to land on the actor’s hand.

Change tracked actor

If you have populated your scene with more than one actor, you can switch tracking from one to another.

First, you need to spawn more than one actor using AMS.

$ parrot-ue4-empty -ams-path=DefaultPath,Pickup:* -ams-path=RunPath,Jasper

A description containing populated paths and their actors should appear once the simulation is launched.

== Paths details ===========================================
Path 'DefaultPath' includes Pickup_0
Path 'RunPath' includes Jasper_0
==============================================================

Now using the web dashboard (or sphinx-cli), you can set the actor_to_track parameter to change the tracked actor (or to start tracking a new one).

Here’s a command line example to set the actor_to_track parameter:

$ sphinx-cli param -m world actors actor_to_track Jasper_0

Customization of AMS

You can customize some aspects of the AMS feature by bringing a YAML configuration file to UE4 app’s command line, as follows.

$ parrot-ue4-empty -config-file=</path/to/file.yaml>

Respecting the YAML format, an AMS configuration file could look like that:

Paths:
  - Name: 'MyAwesomePath'
    SplinePoints:
      - 1.85 -9.5 0.4 Walk 15
      - 15.76 -10.10 0.4 Run 20
      - 17.635 0.85 0.4 Stop 5
      - 17.02 12.03 0.4 Run 20
      - 3.03 14.92 0.4 Walk 15
    ClosedLoop: true
Tags:
  - Name: 'MyAwesomeTag'
    FilePath: '/path/to/MyAwesomeTag.png'
    Width : 30
    Height : 25
    OffsetZ : 10
  - Name: 'MyEvenMoreAwesomeTag'
    FilePath: '/path/to/MyEvenMoreAwesomeTag.png'
    Location : 'Roof'
    Width : 50
    Height : 30
    OffsetX : 10
    OffsetY : 5
    OffsetZ : 20

Two element types can be modified: the paths and the vehicle tags.

Creating custom paths

As shown in the configuration example, all path definitions belong to the same dictionary entry Paths. Each path definition must have the following fields:

• Name- The name of the path.

  Make sure that you don’t choose an already existing path name. You can use the command line -list-paths to visualize the existing paths.

• SplinePoints - A list of the different waypoints of the path. Each

  waypoint is a string containing a location [x y z], an optional attitude, and an optional vehicle speed.

  The location [x y z] is expressed in Gazebo’s coordinate system. You can use the Unreal app’s report window (key P) to visualize and retrieve the Gazebo coordinates of any desired point in the world.

  The optional attitude defines the behavior of the pedestrian beyond the related waypoint. It can be:

  • Walk: Asks the pedestrian to walk (default value).

  • Run: Asks the pedestrian to run.

  • Stop: Asks the pedestrian to stop for 5 seconds then start walking towards the next waypoint.

  The optional vehicle speed defines the new target speed in km/h for vehicles beyond the related waypoint. The default value is 15 km/h. The maximum speed for vehicles is 150 km/h.

  Note

  The proportional-integral-derivative controller (PID controller) used to control the vehicle speed is configured to converge relatively fast. Therefore, it is recommended to limit the speed variation between two successive waypoints.

• ClosedLoop - A boolean that defines whether the path is a closed loop

  or not.

To use the custom path given in the example above, just do like with the predefined paths:

$ parrot-ue4-empty -config-file=</path/to/file.yaml> -ams-path=MyAwesomePath,Jasper

Loading custom tags

As shown in the configuration example, all tag definitions belong to the same dictionary entry Tags. Each tag definition must have the following fields:

• Name- The name of the tag.

• FilePath- The absolute path to the png file.

• Width - The width of the tag in centimeters.

• Height- The height of the tag in centimeters.

• Location - (optional) A string that specifies the position of the tag on the vehicle from a list of a predefined positions for each vehicle. Every single vehicle has a tag location named Default, which is the location used when nothing or something wrong is given. The images below show all the available tag positions and names for each vehicle.

  • Pickup

    

  • Suv

    

  • SportsCar

    

  • Hatchback

    

  • BoxTruck

    

• OffsetX - The offset, in centimeters, added the tag’s location following the X axis in its local reference frame.

• OffsetY - The offset, in centimeters, added the tag’s location following the Y axis in its local reference frame.

• OffsetZ - The offset, in centimeters, added the tag’s location following the Z axis in its local reference frame.

To use the custom tag MyAwesomeTag defined in the example above:

$ parrot-ue4-empty -config-file=</path/to/file.yaml> -ams-path=DefaultPath,Pickup
$ sphinx-cli param -m world actors tags_name MyAwesomeTag