The coordinate system most relevant to a camera sensor in a 3D context is the camera coordinate system, with its origin at the camera's optical center.
Understanding the Camera Coordinate System
The camera coordinate system serves as a crucial reference frame for understanding how a camera perceives the 3D world. It is intrinsically linked to the camera sensor's position and orientation in space.
Origin at the Optical Center
As per the reference, points represented in a camera coordinate system are described with the origin located at the optical center of the camera. This point, also known as the camera's pinhole, is where light rays from the scene theoretically converge.
Axes and Orientation
While the reference doesn't explicitly define the X, Y, and Z axes of the camera coordinate system, it discusses sensor orientation using yaw, pitch, and roll angles that follow an ISO convention. This implies standard axis alignments (e.g., Z typically pointing forward along the optical axis, X horizontally, and Y vertically).
The reference details the positive directions for these sensor orientation angles according to the ISO convention:
- Yaw: Positive clockwise when looking in the positive direction of the Z-axis.
- Pitch: Positive clockwise when looking in the positive direction of the Y-axis.
- Roll: Positive clockwise when looking in the positive direction of the X-axis.
This convention helps define the sensor's rotational pose relative to a reference frame, often tied back to the camera coordinate system axes.
ISO Convention Angle Directions
Here's a quick summary of the angle directions:
| Angle | Axis to look along (positive direction) | Positive Direction |
|---|---|---|
| Yaw | Z-axis | Clockwise |
| Pitch | Y-axis | Clockwise |
| Roll | X-axis | Clockwise |
Relevance to the Sensor
Although the sensor itself is a 2D array of pixels, its position and orientation in 3D space are described relative to the camera coordinate system. Understanding this system is fundamental for:
- Projecting 3D points from the world onto the 2D image plane of the sensor.
- Calculating the camera's pose (position and orientation) in a larger scene.
- Analyzing the geometry of image formation.
In essence, the camera coordinate system provides the 3D frame from which the sensor captures its view of the world, with its origin acting as the camera's central perspective point.
