Projection of laser scan to image plane

edit

I have a laser scan data and camera image. I need to find out the possition of each laser measurement on the image plane. To do that I transformed the laser data ( giving me angle and distance ) to sensor_msgs::Pointcloud2. Now I want to use function cv::projectPoints(...) to project the measured points into the image plane.

My problem is that input format of input pointcloud is 3xN/Nx3 1-channel or 1xN/Nx1 3-channel (or vector<point3f> ). The format of points in Pointcloud2 is usigned char.

How can I do that? I dont even know how to acces the x,y,z coordinates in my cloud.