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Development of a simulator for airborne altimetric LiDAR
The specifications of ALTM 3025 by Optech Inc. have been used in the present case, which gathers up to 25000 points per second, with maximum flying altitude of 3000 m., swath angle varies from 0° to ±20°, and the number of scans from 0 to 70 in one second (ALTM 3025 specifications, http://www.optech.on.ca/altmsys.htm). However, with a little change other sensors and specifications can also be simulated. 3. Methodology for simulation The simulation in case of LiDAR can be categorized in two distinct parts 1) sensor performance and environment 2) Nature of terrain. The former in the present case is implemented by considering a straight line path of aircraft between two points, input by user, for starting and finishing position of aircraft which in real are given by a kinematic differential GPS, mounted on top of aircraft. User also defines the swath angle and number of scans desired to carry out simulation. In accordance with the above defined parameters, the instantaneous coordinates of aircraft and direction of laser beam are calculated. Equation of laser vector thus is given by:  .... (2.1) Where,  and ω, γ and κ are absolute angles with positive x, y and z axes respectively, and X0, Y0, Z0 are instantaneous coordinates of aircraft at the time of firing the pulse (Figure 1). In the present case it is assumed that there are no roll, pitch, and heading movement of aircraft, though the same will be accounted for in future.
The second part of simulation is the nature of terrain, for which LiDAR data is being gathered. This terrain can be represented by mathematical surfaces. The following paragraphs describe the procedure for generating LiDAR data on these surfaces. Surfaces ranging from simple planar surfaces to complex i.e. combination of multiple surfaces have been discussed. The simple surfaces have equations of the form of  having no border limitations. X and Y from equation (2.1) are put into the equation of surface and a simple equation of the form of 
is obtained which is solved for Z. Now from equation (2.1) again the value of X and Y corresponding to Z obtained above is calculated i. e.
 The surfaces of the above form are: 1. Plane surface (Ax +By +Cz +D =0) (Figure 2.1),  2. Cone (z2 =x2+y2) (Figure 2.2),   3. z =x2+y2 (Figure 2.3).  |