<h1>Measurements</h1>

!!! important
    Since version 0.8.0 the measurements received by the client are in SI
    units. All locations have been converted to `meters` and speeds to
    `meters/second`.

Every frame the server sends a package with the measurements and images gathered
to the client. This document describes the details of these measurements.

Time-stamps
-----------

Every frame is described by three different counters/time-stamps

Key                        | Type      | Units        | Description
-------------------------- | --------- | ------------ | ------------
frame_number               | uint64    |              | Frame counter (it is **not** restarted on each episode).
platform_timestamp         | uint32    | milliseconds | Time-stamp of the current frame, as given by the OS.
game_timestamp             | uint32    | milliseconds | In-game time-stamp, elapsed since the beginning of the current episode.

In real-time mode, the elapsed time between two time steps should be similar
both platform and game time-stamps. When run in fixed-time step, the game
time-stamp increments in constant time steps (delta=1/FPS) while the platform
time-stamp keeps the actual time elapsed.

Player measurements
-------------------

Key                        | Type        | Units  | Description
-------------------------- | ----------- | ------ | ------------
transform                  | Transform   |        | World transform of the player (contains a locations and a rotation) respect the vehicle's mesh pivot.
bounding_box               | BoundingBox |        | Bounding box of the player.
acceleration               | Vector3D    | m/s^2  | Current acceleration of the player.
forward_speed              | float       | m/s    | Forward speed of the player.
collision_vehicles         | float       | kg*m/s | Collision intensity with other vehicles.
collision_pedestrians      | float       | kg*m/s | Collision intensity with pedestrians.
collision_other            | float       | kg*m/s | General collision intensity (everything else but pedestrians and vehicles).
intersection_otherlane     | float       |        | Percentage of the vehicle invading other lanes.
intersection_offroad       | float       |        | Percentage of the vehicle off-road.
autopilot_control          | Control     |        | Vehicle's autopilot control that would apply this frame.

<h4>Transform</h4>

The transform contains the location and rotation of the player.

Key                        | Type       | Units   | Description
-------------------------- | ---------- | ------- | ------------
location                   | Vector3D   | m       | World location.
orientation *[deprecated]* | Vector3D   |         | Orientation in Cartesian coordinates.
rotation                   | Rotation3D | degrees | Pitch, roll, and yaw.

<h4>BoundingBox</h4>

Contains the transform and extent of a bounding box.

Key                        | Type       | Units   | Description
-------------------------- | ---------- | ------- | ------------
transform                  | Transform  |         | Transform of the bounding box relative to the vehicle.
extent                     | Vector3D   | m       | Radii dimensions of the bounding box (half-box).

<h4>Collision</h4>

Collision variables keep an accumulation of all the collisions occurred during
this episode. Every collision contributes proportionally to the intensity of the
collision (norm of the normal impulse between the two colliding objects).

Three different counts are kept (pedestrians, vehicles, and other). Colliding
objects are classified based on their tag (same as for semantic segmentation).

!!! Bug
    See [#13 Collisions are not annotated when vehicle's speed is low](https://github.com/carla-simulator/carla/issues/13)

Collisions are not annotated if the vehicle is not moving (<1km/h) to avoid
annotating undesired collision due to mistakes in the AI of non-player agents.

<h4>Lane/off-road intersection</h4>

The lane intersection measures the percentage of the vehicle invading the
opposite lane. The off-road intersection measures the percentage of the vehicle
outside the road.

These values are computed intersecting the bounding box of the vehicle (as a 2D
rectangle) against the map image of the city. These images are generated in the
editor and serialized for runtime use. You can find them too in the release
package under the folder "RoadMaps".

<h4>Autopilot control</h4>

The `autopilot_control` measurement contains the control values that the in-game
autopilot system would apply as if it were controlling the vehicle.

This is the same structure used to send the vehicle control to the server.

Key                        | Type      | Description
-------------------------- | --------- | ------------
steer                      | float     | Steering angle between [-1.0, 1.0] (*)
throttle                   | float     | Throttle input between [ 0.0, 1.0]
brake                      | float     | Brake input between [ 0.0, 1.0]
hand_brake                 | bool      | Whether the hand-brake is engaged
reverse                    | bool      | Whether the vehicle is in reverse gear

To activate the autopilot from the client, send this `autopilot_control` back
to the server. Note that you can modify it before sending it back.

```py
measurements, sensor_data = carla_client.read_data()
control = measurements.player_measurements.autopilot_control
# modify here control if wanted.
carla_client.send_control(control)
```

(*) The actual steering angle depends on the vehicle used. The default Mustang
has a maximum steering angle of 70 degrees (this can be checked in the vehicle's
front wheel blueprint).

![Mustan Steering Angle](img/steering_angle_mustang.png)

Non-player agents info
----------------------

!!! important
    Since version 0.8.0 the player vehicle is not sent in the list of non-player
    agents.

To receive info of every non-player agent in the scene every frame you need to
activate this option in the settings file sent by the client at the beginning of
the episode.

```ini
[CARLA/Server]
SendNonPlayerAgentsInfo=true
```

If enabled, the server attaches a list of agents to the measurements package
every frame. Each of these agents has an unique id that identifies it, and
belongs to one of the following classes

  * Vehicle
  * Pedestrian
  * Traffic ligth
  * Speed limit sign

Each of them can be accessed in Python by checking if the agent object has the
field enabled

```python
measurements, sensor_data = client.read_data()

for agent in measurements.non_player_agents:
    agent.id # unique id of the agent
    if agent.HasField('vehicle'):
        agent.vehicle.forward_speed
        agent.vehicle.transform
        agent.vehicle.bounding_box
```

<h6>Vehicle</h6>

Key                             | Type      | Description
------------------------------- | --------- | ------------
id                              | uint32    | Agent ID
vehicle.forward_speed           | float     | Forward speed of the vehicle in m/s, is the linear speed projected to the forward vector of the chassis of the vehicle
vehicle.transform               | Transform | Agent-to-world transform
vehicle.bounding_box.transform  | Transform | Transform of the bounding box relative to the vehicle
vehicle.bounding_box.extent     | Vector3D  | Radii dimensions of the bounding box in meters

<h6>Pedestrian</h6>

Key                               | Type      | Description
--------------------------------- | --------- | ------------
id                                | uint32    | Agent ID
pedestrian.forward_speed          | float     | Forward speed of the pedestrian in m/s
pedestrian.transform              | Transform | Agent-to-world transform
pedestrian.bounding_box.transform | Transform | Transform of the bounding box relative to the pedestrian
pedestrian.bounding_box.extent    | Vector3D  | Radii dimensions of the bounding box in meters (*)

<small>(*) At this point every pedestrian is assumed to have the same
bounding-box size.</small>

<h6>Traffic light</h6>

Key                          | Type      | Description
---------------------------- | --------- | ------------
id                           | uint32    | Agent ID
traffic_light.transform      | Transform | Agent-to-world transform
traffic_light.state          | enum      | Traffic light state; `GREEN`, `YELLOW`, or `RED`

<h6>Speed limit sign</h6>

Key                          | Type      | Description
---------------------------- | --------- | ------------
id                           | uint32    | Agent ID
speed_limit_sign.transform   | Transform | Agent-to-world transform
speed_limit_sign.speed_limit | float     | Speed limit in m/s

<h4>Transform and bounding box</h4>

The transform defines the location and orientation of the agent. The transform
of the bounding box is given relative to the vehicle. The box extent gives the
radii dimensions of the bounding box of the agent.

![Vehicle Bounding Box](img/vehicle_bounding_box.png)