title: Projection of 3D Lidar point in the i-th camera image (KITTI Dataset)
body: <p>I am working on a object classification problem and I am using Lidar and camera data from the Kitti Dataset.,
  In this article : <a href="http://ww.cvlibs.net/publications/Geiger2013IJRR.pdf" rel="nofollow noreferrer">http://ww.cvlibs.net/publications/Geiger2013IJRR.pdf</a> , they provide the formulas for projecting the 3d PointCloud into the i-th camera image plane, but I don't understand some things :</p>
  <p>Following equation((3) :</p>
  <p>If the 3D point X is in velodyne camera image and Y in the i'th camera image, why X has four coordinates and Y three? It should have been 3 and 2, no?</p>
  <p><a href="https://i.stack.imgur.com/LfqWR.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LfqWR.png" alt="Formula" /></a><br />
  <sub>(source: <a href="https://image.noelshack.com/fichiers/2019/22/3/1559117284-1.png" rel="nofollow noreferrer">noelshack.com</a>)</sub></p>
  <p>I need to project the 3D point Cloud into the camera image plane for then creating lidar images to use them as a channel for the CNN. Anyone who has ideas for it ?</p>
  <p>Thanks you in advance</p>