Airborne 3D imager, which integrates global positioning system (GPS), attitude measurement
unit (AMU), scanning laser range finder(SLR) and spectrum imager, is a new airborne remote sensing
technology system. It can generate geo-referenced image (orthographic image) without ground control
points and it uses the laser points distributed in the image to rectify raw image. SLR and spectrum imager
use the same optical system which ensure the image and laser point to be matched closely. The calculation
of 3D position of laser point is the key to the 3D imager. According to geometry principle, the position of
laser point can be determined if the space position of airplane is surveyed by GPS, the attitude of the
airplane is surveyed by AMU and the range from air to ground is measured by SLR. In this paper the
principle and data structure of 3D imager is introduced first, then the procedure of calculating the position
of laser point is presented in detail based on the design principle of the imager. A processing example that
is a part of flight test in South China is given in the end to verify the feasibility of the algorithm.