컴퓨터 비전(광류 센서, 움직임 감지, 관성 주행 시각 측정, 회피)
컴퓨터 비전은 컴퓨터가 시각 데이터를 활용하여 실제 환경을 이해하는 기술입니다.
PX4 uses computer vision systems (primarily running on Companion Computers) in order to support the following features:
- 광류(Optical flow)는 2D 속도 추정을 제공합니다(아래로 향하는 카메라와 아래로 향하는 거리 센서 사용).
- Motion Capture provides 3D pose estimation using a vision system that is external to the vehicle. 주로 실내 내비게이션에 사용됩니다.
- Visual Inertial Odometry는 온보드 비전 시스템과 IMU를 사용하여 3D 자세 및 속도 추정을 제공합니다. It is used for navigation when GNSS position information is absent or unreliable.
- 장애물 회피는 계획된 경로를 비행시 장애물 주위를 탐색합니다(현재 임무가 지원됨). This uses PX4/PX4-Avoidance running on a companion computer.
- 충돌 방지는 장애물에 충돌하기 전에 차량을 멈추는 데 사용됩니다(주로 수동 모드에서 비행할 때).
TIP
PX4 Vision Autonomy Development Kit(Holybro)는 PX4에서 컴퓨터 비전으로 작업하는 개발자를 위한 강력하고 저렴한 키트입니다. It comes with no pre-installed software, but does include an example implementation of obstacle avoidance to demonstrate the capabilities of the platform.
모션 캡쳐
Motion Capture (MoCap) is a technique for estimating the 3D pose (position and orientation) of a vehicle using a positioning mechanism that is external to the vehicle. MoCap systems most commonly detect motion using infrared cameras, but other types of cameras, Lidar, or Ultra Wideband (UWB) may also be used.
MoCap is commonly used to navigate a vehicle in situations where GPS is absent (e.g. indoors), and provides position relative to a local coordinate system.
MoCap 기술에 대해 더 알아보려면 다음을 참고하십시오:
시각적 관성 주행 거리 측정(VIO)
Visual Inertial Odometry (VIO) is used for estimating the 3D pose (position and orientation) and velocity of a moving vehicle relative to a local starting position. 보통 GPS가 빠졌거나 (예: 실내) 신뢰할 수 없을 때(예: 다리 아래로 비행할 경우) 기체 운행에 활용합니다.
VIO uses Visual Odometry to estimate vehicle pose from visual information, combined with inertial measurements from an IMU (to correct for errors associated with rapid vehicle movement resulting in poor image capture).
:::note VIO와 MoCap의 한 가지 차이점은 VIO 카메라/IMU가 차량 기반이며 추가로 속도 정보를 제공하는 것입니다. :::
PX4의 VIO 설정 방법을 더 알아보려면 다음을 참고하십시오:
광류
광류 센서(Optical Flow) 기술로 2차원 평면상의 속도를 추정합니다(아래 방향으로 향한 카메라와 아래 방향으로 향한 거리 센서 활용).
광류 센서 기술을 더 알아보려면 다음을 참고하십시오.
Comparisons
Optical Flow vs VIO for Local Position Estimation
Both these techniques use cameras and measure differences between frames. Optical flow uses a downward facing camera, while VIO uses a stereo camera or a 45 degree tracking camera. Assuming both are well calibrated, which is better for local position estimation?
The consensus appears to be:
Optical flow:
- Downward facing optical flow gives you a planar velocity thats corrected for angular velocity with the gyro.
- Requires an accurate distance to the ground and assumes a planar surface. Given those conditions it can be just as accurate/reliable as VIO (such as indoor flight)
- Is more robust than VIO as it has fewer states.
- Is significantly cheaper and easier to set up as it only requires a flow sensor, a rangefinder, and setting up a few parameters (which can be connected to the flight controller).
VIO:
- Is more expensive to purchase and harder to set up. It requires a separate companion computer, calibration, software, configuration and so on.
- Will be less effective if there are no point features to track (in practice the real world generally has point features).
- Is more flexible, allowing additional features such as obstacle avoidance and mapping.
A combination (fusing both) is probably the most reliable, though not necessary in most real-world scenarios. Normally you will select the system that suits your operating environment, required features, and cost constraints:
- Use VIO if you plan on flying outdoors without GPS (or outdoors and indoors), or if you need to support obstacle avoidance and other computer vision features.
- Use Optical Flow if you plan on only flying indoors (without GPS) and cost is an important consideration.
외부 참고 자료
- XTDrone - 컴퓨터 비전용 ROS + PX4 시뮬레이션 환경입니다. XTDrone 설명서에 시작에 필요한 모든 내용이 들어있습니다!