> For the complete documentation index, see [llms.txt](https://px4.gitbook.io/px4-user-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://px4.gitbook.io/px4-user-guide/drone_parts/companion_computer/computer_vision.md).

# Computer Vision

[Computer vision](https://en.wikipedia.org/wiki/Computer_vision) techniques enable computers to use visual data to make sense of their environment.

PX4 uses computer vision systems (primarily running on [Companion Computers](/px4-user-guide/drone_parts/companion_computer.md)) in order to support the following features:

* Pose/Velocity Estimation:
  * [Optical Flow](/px4-user-guide/drone_parts/peripherals/optical_flow.md) provides 2D velocity estimation (using a downward facing camera and a downward facing distance sensor).
  * [Motion Capture](/px4-user-guide/drone_parts/companion_computer/computer_vision/motion_capture.md) provides 3D pose estimation using a vision system that is *external* to the vehicle. It is primarily used for indoor navigation.
  * [Visual Inertial Odometry (VIO)](/px4-user-guide/drone_parts/companion_computer/computer_vision/visual_inertial_odometry.md) provides 3D pose and velocity estimation using an onboard vision system and IMU. It is used for navigation when global position information is absent or unreliable.
* Avoidance/Path Planning:
  * [Obstacle Avoidance](/px4-user-guide/drone_parts/companion_computer/computer_vision/obstacle_avoidance.md) provides full navigation around obstacles when flying a planned path (currently missions are supported). This uses [PX4/PX4-Avoidance](https://github.com/PX4/PX4-Avoidance) running on a companion computer.
  * [Collision Prevention](/px4-user-guide/drone_parts/companion_computer/computer_vision/collision_prevention.md) is used to stop vehicles before they can crash into an obstacle (primarily when flying in manual modes).
  * [Safe Landing](/px4-user-guide/drone_parts/companion_computer/computer_vision/safe_landing.md) guides vehicles to find (and land on) flat terrain that is free of stationary obstacles.

:::tip The [PX4 Vision Autonomy Development Kit](/px4-user-guide/drone_parts/complete_vehicles/px4_vision_kit.md) (Holybro) is a robust and inexpensive kit for developers working with computer vision on PX4. It comes with no pre-installed software, but does include an example implementation of obstacle avoidance to demonstrate the capabilities of the platform. :::

## External Resources

* [XTDrone](https://github.com/robin-shaun/XTDrone/blob/master/README.en.md) - ROS + PX4 v1.9 simulation environment for computer vision. The [XTDrone Manual](https://www.yuque.com/xtdrone/manual_en) has everything you need to get started!