In LiDAR surveying the following basic measurements are obtained for each laser pulse fired:
· Laser range by measuring ToT of a pulse
· Laser scan angle
· Aircraft roll, pitch and yaw
· Aircraft acceleration in three directions
· GPS antenna coordinates
Geo-location means how to determine the coordinates of laser footprint in WGS-84 reference system by combining the aforesaid basic measurements.
As seen in Figure 15, a LiDAR system consists of three main sensors, viz. LiDAR scanner, INS and GPS. These systems operate at their respective frequencies. The laser range vector which is fired at an scan angle η in the reference frame of laser instrument will need to be finally transformed the earth cantered WGS-84 system for realising the geolocation of the laser footprint. This transformation is carried through various rotations and transformatios as shown below. First it is important to understand the various coordinate systems involved in this process and their relationships.