Get 3d coordinates by 2d point on camview

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Hi!, I have calibrated camera (i have camera_matrix, distortion_coefficients, projection_matrix). My cam is pointed to a wall. When I choose a point on 2d image (camera view capture), I would like to get a point of wall in world coordinates, assuming that cam is coordinate origin and distance from cam to real point on wall is known. Could you please help me how to do it? Regards,