Cameras and sensors

Client window

Sensors are a special type of actor able to measure and stream data. All the sensors have a listen method that registers the callback function that will be called each time the sensor produces a new measurement. Sensors are typically attached to vehicles and produce data either each simulation update, or when a certain event is registered.

The following Python excerpt shows how you would typically attach a sensor to a vehicle, in this case we are adding a dashboard HD camera to a vehicle.

# Find the blueprint of the sensor.
blueprint = world.get_blueprint_library().find('sensor.camera.rgb')
# Modify the attributes of the blueprint to set image resolution and field of view.
blueprint.set_attribute('image_size_x', '1920')
blueprint.set_attribute('image_size_y', '1080')
blueprint.set_attribute('fov', '110')
# Set the time in seconds between sensor captures
blueprint.set_attribute('sensor_tick', '1.0')
# Provide the position of the sensor relative to the vehicle.
transform = carla.Transform(carla.Location(x=0.8, z=1.7))
# Tell the world to spawn the sensor, don't forget to attach it to your vehicle actor.
sensor = world.spawn_actor(blueprint, transform, attach_to=my_vehicle)
# Subscribe to the sensor stream by providing a callback function, this function is
# called each time a new image is generated by the sensor.
sensor.listen(lambda data: do_something(data))

Note that each sensor has a different set of attributes and produces different type of data. However, the data produced by a sensor comes always tagged with:

Sensor data attribute Type Description
frame int Frame number when the measurement took place
timestamp double Timestamp of the measurement in simulation seconds since the beginning of the episode
transform carla.Transform Transform in world coordinates of the sensor at the time of the measurement

Most sensor data objects, like images and lidar measurements, have a function for saving the measurements to disk.

This is the list of sensors currently available

Camera sensors use carla.colorConverter in order to convert the pixels of the original image.

sensor.camera.rgb

ImageRGB

The "RGB" camera acts as a regular camera capturing images from the scene.

Basic camera attributes

Blueprint attribute Type Default Description
sensor_tick float 0.0 Seconds between sensor captures (ticks)
image_size_x int 800 Image width in pixels
image_size_y int 600 Image height in pixels
gamma float 2.2 Target gamma value of the camera
fov float 90.0 Horizontal field of view in degrees
shutter_speed float 60.0 The camera shutter speed in seconds (1.0 / s)
iso float 1200.0 The camera sensor sensitivity
fstop float 1.4 Defines the opening of the camera lens. Aperture is 1 / fstop with typical lens going down to f / 1.2 (larger opening). Larger numbers will reduce the Depth of Field effect

Camera lens distortion attributes

Blueprint attribute Type Default Description
lens_circle_falloff float 5.0 Range: [0.0, 10.0]
lens_circle_multiplier float 0.0 Range: [0.0, 10.0]
lens_k float -1.0 Range: [-inf, inf]
lens_kcube float 0.0 Range: [-inf, inf]
lens_x_size float 0.08 Range: [0.0, 1.0]
lens_y_size float 0.08 Range: [0.0, 1.0]

Advanced camera attributes

Since these effects are provided from Unreal Engine 4, please make sure to check their documentation on how they work and the relation between them:

Blueprint attribute Type Default Description
min_fstop float 1.2 Maximum Aperture
blade_count int 5 The number of blades that make up the diaphragm mechanism
exposure_mode str "manual" Can be "manual" or "histogram". More info in UE4 official docs
exposure_compensation float 3.0 Logarithmic adjustment for the exposure. 0: no adjustment, -1:2x darker, -2:4 darker, 1:2x brighter, 2:4x brighter
exposure_min_bright float 0.1 Used when exposure_mode:"histogram" The minimum brightness for auto exposure that limits the lower brightness the eye can adapt within. Values must be greater than 0 and should be less than or equal to exposure_max_bright
exposure_max_bright float 2.0 Used when exposure_mode:"histogram" The maximum brightness for auto exposure that limits the upper brightness the eye can adapt within. Values must be greater 0 and should be greater than or equal to exposure_min_bright
exposure_speed_up float 3.0 Used when exposure_mode:"histogram" The speed at which the adaptation occurs from a dark environment to a bright environment
exposure_speed_down float 1.0 Used when exposure_mode:"histogram" The speed at which the adaptation occurs from a bright environment to a dark environment
calibration_constant float 16.0 Calibration constant for 18% Albedo
focal_distance float 1000.0 The distance in which the depth of field effect should be sharp. This value is measured in Unreal Units (cm)
blur_amount float 1.0 Strength/intensity of motion blur
blur_radius float 0.0 Radius in pixels at 1080p resolution to apply according to distance from camera to emulate atmospheric scattering
motion_blur_intensity float 0.45 Strength of motion blur. 1 is max and 0 is off
motion_blur_max_distortion float 0.35 Max distortion caused by motion blur, in percent of the screen width, 0 is off
motion_blur_min_object_screen_size float 0.1 Percentage of screen width objects must have for motion blur, lower value means less draw calls
slope float 0.88 This will adjust the steepness of the S-curve used for the tonemapper, where larger values will make the slope steeper (darker) and lower values will make the slope less steep (lighter). Range: [0.0, 1.0]
toe float 0.55 This will adjust the dark color in the tonemapper. Range: [0.0, 1.0]
shoulder float 0.26 This will adjust the bright color in the tonemapper. Range: [0.0, 1.0]
black_clip float 0.0 This will set where the crossover happens when black tones start to cut off their value. In general, this value should NOT be adjusted. Range: [0.0, 1.0]
white_clip float 0.04 This will set where the crossover happens when white tones start to cut off their value. This will appear as a subtle change in most cases. Range: [0.0, 1.0]
temp float 6500.0 This will adjust the white balance in relation to the temperature of the light in the scene. When the light temperature and this one match, the light will appear white. When a value is used that is higher than the light in the scene it will yield a "warm" or yellow color, and, conversely, if the value is lower, it would yield a "cool" or blue color
tint float 0.0 This will adjust the white balance temperature tint for the scene by adjusting the cyan and magenta color ranges. Ideally, this setting should be used once you've adjusted the white balance Temp property to get accurate colors. Under some light temperatures, the colors may appear to be more yellow or blue. This can be used to balance the resulting color to look more natural
chromatic_aberration_intensity float 0.0 Scaling factor that controls how much color shifting occurs, more noticable on the screen borders
chromatic_aberration_offset float 0.0 Normalized distance to the center of the image where the effect takes place
enable_postprocess_effects bool True Whether the post-process effect in the scene affects the image

The sensor_tick tells how fast we want the sensor to capture the data. A value of 1.5 means that we want the sensor to capture data each second and a half. By default a value of 0.0 means as fast as possible.

Output attributes

This sensor produces carla.Image objects.

Sensor data attribute Type Description
frame int Frame number when the measurement took place
timestamp double Timestamp of the measurement in simulation seconds since the beginning of the episode
transform carla.Transform Transform in world coordinates of the sensor at the time of the measurement
width int Image width in pixels
height int Image height in pixels
fov float Horizontal field of view in degrees
raw_data bytes Array of BGRA 32-bit pixels

sensor.camera.depth

ImageDepth

The "Depth" camera provides a view over the scene codifying the distance of each pixel to the camera (also known as depth buffer or z-buffer).

Basic camera attributes

Blueprint attribute Type Default Description
image_size_x int 800 Image width in pixels
image_size_y int 600 Image height in pixels
fov float 90.0 Horizontal field of view in degrees
sensor_tick float 0.0 Seconds between sensor captures (ticks)

Camera lens distortion attributes

Blueprint attribute Type Default Description
lens_circle_falloff float 5.0 Range: [0.0, 10.0]
lens_circle_multiplier float 0.0 Range: [0.0, 10.0]
lens_k float -1.0 Range: [-inf, inf]
lens_kcube float 0.0 Range: [-inf, inf]
lens_x_size float 0.08 Range: [0.0, 1.0]
lens_y_size float 0.08 Range: [0.0, 1.0]

Output attributes

This sensor produces carla.Image objects.

Sensor data attribute Type Description
frame int Frame number when the measurement took place
timestamp double Timestamp of the measurement in simulation seconds since the beginning of the episode
transform carla.Transform Transform in world coordinates of the sensor at the time of the measurement
width int Image width in pixels
height int Image height in pixels
fov float Horizontal field of view in degrees
raw_data bytes Array of BGRA 32-bit pixels

The image codifies the depth in 3 channels of the RGB color space, from less to more significant bytes: R -> G -> B. The actual distance in meters can be decoded with

normalized = (R + G * 256 + B * 256 * 256) / (256 * 256 * 256 - 1)
in_meters = 1000 * normalized

sensor.camera.semantic_segmentation

ImageSemanticSegmentation

The "Semantic Segmentation" camera classifies every object in the view by displaying it in a different color according to the object class. E.g., pedestrians appear in a different color than vehicles.

Basic camera attributes

Blueprint attribute Type Default Description
image_size_x int 800 Image width in pixels
image_size_y int 600 Image height in pixels
fov float 90.0 Horizontal field of view in degrees
sensor_tick float 0.0 Seconds between sensor captures (ticks)

Camera lens distortion attributes

Blueprint attribute Type Default Description
lens_circle_falloff float 5.0 Range: [0.0, 10.0]
lens_circle_multiplier float 0.0 Range: [0.0, 10.0]
lens_k float -1.0 Range: [-inf, inf]
lens_kcube float 0.0 Range: [-inf, inf]
lens_x_size float 0.08 Range: [0.0, 1.0]
lens_y_size float 0.08 Range: [0.0, 1.0]

Output attributes

This sensor produces carla.Image objects.

Sensor data attribute Type Description
frame int Frame number when the measurement took place
timestamp double Timestamp of the measurement in simulation seconds since the beginning of the episode
transform carla.Transform Transform in world coordinates of the sensor at the time of the measurement
width int Image width in pixels
height int Image height in pixels
fov float Horizontal field of view in degrees
raw_data bytes Array of BGRA 32-bit pixels

The server provides an image with the tag information encoded in the red channel. A pixel with a red value of x displays an object with tag x. The following tags are currently available

Value Tag Converted color
0 Unlabeled ( 0, 0, 0)
1 Building ( 70, 70, 70)
2 Fence (190, 153, 153)
3 Other (250, 170, 160)
4 Pedestrian (220, 20, 60)
5 Pole (153, 153, 153)
6 Road line (157, 234, 50)
7 Road (128, 64, 128)
8 Sidewalk (244, 35, 232)
9 Vegetation (107, 142, 35)
10 Car ( 0, 0, 142)
11 Wall (102, 102, 156)
12 Traffic sign (220, 220, 0)

This is implemented by tagging every object in the scene before hand (either at begin play or on spawn). The objects are classified by their relative file path in the project. E.g., every mesh stored in the "Unreal/CarlaUE4/Content/Static/Pedestrians" folder it's tagged as pedestrian.

Note

Adding new tags: At the moment adding new tags is not very flexible and requires to modify the C++ code. Add a new label to the ECityObjectLabel enum in "Tagger.h", and its corresponding filepath check inside GetLabelByFolderName() function in "Tagger.cpp".

sensor.lidar.ray_cast

LidarPointCloud

This sensor simulates a rotating Lidar implemented using ray-casting. The points are computed by adding a laser for each channel distributed in the vertical FOV, then the rotation is simulated computing the horizontal angle that the Lidar rotated this frame, and doing a ray-cast for each point that each laser was supposed to generate this frame; points_per_second / (FPS * channels).

Lidar attributes

Blueprint attribute Type Default Description
channels int 32 Number of lasers
range float 10.0 Maximum measurement distance in meters (<=0.9.6: is in centimeters)
points_per_second int 56000 Points generated by all lasers per second
rotation_frequency float 10.0 Lidar rotation frequency
upper_fov float 10.0 Angle in degrees of the upper most laser
lower_fov float -30.0 Angle in degrees of the lower most laser
sensor_tick float 0.0 Seconds between sensor captures (ticks)

Output attributes

This sensor produces carla.LidarMeasurement objects.

Sensor data attribute Type Description
frame int Frame number when the measurement took place
timestamp double Timestamp of the measurement in simulation seconds since the beginning of the episode
transform carla.Transform Transform in world coordinates of the sensor at the time of the measurement
horizontal_angle float Angle in XY plane of the lidar this frame (in radians)
channels int Number of channels (lasers) of the lidar
get_point_count(channel) int Number of points per channel captured this frame
raw_data bytes Array of 32-bits floats (XYZ of each point)

The object also acts as a Python list of carla.Location

for location in lidar_measurement:
    print(location)

A Lidar measurement contains a packet with all the points generated during a 1/FPS interval. During this interval the physics is not updated so all the points in a measurement reflect the same "static picture" of the scene.

Tip

Running the simulator at fixed time-step it is possible to tune the horizontal angle of each measurement. By adjusting the frame rate and the rotation frequency is possible, for instance, to get a 360 view each measurement.

sensor.other.collision

This sensor, when attached to an actor, it registers an event each time the actor collisions against something in the world. This sensor does not have any configurable attribute.

Note

This sensor creates "fake" actors when it collides with something that is not an actor, this is so we can retrieve the semantic tags of the object we hit.

Output attributes

This sensor produces a carla.CollisionEvent object for each collision registered

Sensor data attribute Type Description
frame int Frame number when the measurement took place
timestamp double Timestamp of the measurement in simulation seconds since the beginning of the episode
transform carla.Transform Transform in world coordinates of the sensor at the time of the measurement
actor carla.Actor Actor that measured the collision ("self" actor)
other_actor carla.Actor Actor against whom we collide
normal_impulse carla.Vector3D Normal impulse result of the collision

Note that several collision events might be registered during a single simulation update.

sensor.other.lane_invasion

This sensor is a work in progress, currently very limited.

This sensor, when attached to an actor, it registers an event each time the actor crosses a lane marking. This sensor is somehow special as it works fully on the client-side. The lane invasion uses the road data of the active map to determine whether a vehicle is invading another lane. This information is based on the OpenDrive file provided by the map, therefore it is subject to the fidelity of the OpenDrive description. In some places there might be discrepancies between the lanes visible by the cameras and the lanes registered by this sensor.

This sensor does not have any configurable attribute.

Output attributes

This sensor produces a carla.LaneInvasionEvent object for each lane marking crossed by the actor

Sensor data attribute Type Description
frame int Frame number when the measurement took place
timestamp double Timestamp of the measurement in simulation seconds since the beginning of the episode
transform carla.Transform Transform in world coordinates of the sensor at the time of the measurement
actor carla.Actor Actor that invaded another lane ("self" actor)
crossed_lane_markings carla.LaneMarking list List of lane markings that have been crossed

sensor.other.gnss

This sensor, when attached to an actor, reports its current gnss position. The gnss position is internally calculated by adding the metric position to an initial geo reference location defined within the OpenDRIVE map definition.

Output attributes

This sensor produces carla.GnssEvent objects.

Sensor data attribute Type Description
frame int Frame number when the measurement took place
timestamp double Timestamp of the measurement in simulation seconds since the beginning of the episode
transform carla.Transform Transform in world coordinates of the sensor at the time of the measurement
latitude double Latitude position of the actor
longitude double Longitude position of the actor
altitude double Altitude of the actor

sensor.other.obstacle

This sensor, when attached to an actor, reports if there is obstacles ahead.

Note

This sensor creates "fake" actors when it detects obstacles with something that is not an actor, this is so we can retrieve the semantic tags of the object we hit.

Blueprint attribute Type Default Description
distance float 5 Distance to throw the trace to
hit_radius float 0.5 Radius of the trace
only_dynamics bool false If true, the trace will only look for dynamic objects
debug_linetrace bool false If true, the trace will be visible
sensor_tick float 0.0 Seconds between sensor captures (ticks)

Output attributes

This sensor produces carla.ObstacleDetectionEvent objects.

Sensor data attribute Type Description
frame int Frame number when the measurement took place
timestamp double Timestamp of the measurement in simulation seconds since the beginning of the episode
transform carla.Transform Transform in world
actor carla.Actor Actor that detected the obstacle ("self" actor)
other_actor carla.Actor Actor detected as obstacle
distance float Distance from actor to other_actor

sensor.other.imu

This sensor, when attached to an actor, the user can access to it's accelerometer, gyroscope and compass.

Output attributes

This sensor produces carla.IMUMeasurement objects.

Sensor data attribute Type Description
frame int Frame number when the measurement took place
timestamp double Timestamp of the measurement in simulation seconds since the beginning of the episode
transform carla.Transform Transform in world
accelerometer carla.Vector3D Measures linear acceleration in m/s^2
gyroscope carla.Vector3D Measures angular velocity in rad/sec
compass float Orientation with respect to the North ((0.0, -1.0, 0.0) in Unreal) in radians