What is the definition of depth in the task of depth completion - KITTI dataset

Question

What is the depth definition of the pixels in an image? In the sketch map as following, if the target position of the red star represent the pixels with depth in its corresponding image, I am not sure which of the following definitions of depth is right

(1) the distance between camera and target position;
(2) the distance between laser scanner and target position;
(3) the z-axis value (camera coordinate system) of the target position;
(4) the x-axis value (laser scanner coordinate system) of the target position.

Is there any standard definition of depth?

Answer 1

The depth in each pixel is the distance to the camera sensor, not the lidar, in order to have rgb/depth matching rasters. The x coordinate of the point cloud has nothing to do with the depth.