cspice_surfpt |
|||

## AbstractCSPICE_SURFPT determines the intersection of a line-of-sight vector with the surface of an ellipsoid. ## I/OGiven: positn the position of an observer with respect to the center of an ellipsoid expressed in the body fixed coordinates of the ellipsoid [3,1] = size(positn); double = class(positn) u the direction vector emanating from 'positn'. [3,1] = size(u); double = class(u) a, the ellipsoid's triaxial radii, where: b, c 'a' is length in kilometers of the semi-axis of the ellipsoid parallel to the x-axis of the body-fixed reference frame [1,1] = size(a); double = class(a) 'b' is length in kilometers of the semi-axis of the ellipsoid parallel to the y-axis of the body-fixed reference frame [1,1] = size(b); double = class(b) 'c' is length in kilometers of the semi-axis of the ellipsoid parallel to the z-axis of the body-fixed reference frame [1,1] = size(c); double = class(c) the call: [point, found] = ## ExamplesAny numerical results shown for this example may differ between platforms as the results depend on the SPICE kernels used as input and the machine specific arithmetic implementation. Suppose that MGS has taken a picture of Mars at time 'etrec' with the MOC narrow angle camera. We want to know the latitude and longitude associated with two pixels projected to Mars' surface: the boresight and one along the boundary of the field of view (FOV). Due to light time, the photons taken in the picture left Mars at time 'etemit', when Mars was at a different state than at time 'etrec'. In order to solve this problem, we could use the 'cspice_sincpt' routine for both pixels, but this would be slow. Instead, we will assume that the light time for each pixel is the same. We will call 'cspice_sincpt' once to get the light time and surface point associated with the boresight. Then, we will rotate the first FOV boundary vector from the camera frame at 'etrec' to the body-fixed Mars frame at 'etemit', and call the faster routine ' ## ParticularsNone. ## Required ReadingFor important details concerning this module's function, please refer to the CSPICE routine surfpt_c. MICE.REQ ELLIPSES.REQ ## Version-Mice Version 1.0.1, 05-NOV-2015, EDW (JPL) Corrected Index_Entries and Usage string. Edited I/O section to conform to NAIF standard for Mice documentation. -Mice Version 1.0.0, 24-OCT-2011, SCK (JPL) ## Index_Entriesline of sight intercept with body point of intersection between ray and ellipsoid surface point of intersection of ray and ellipsoid |

Wed Apr 5 18:00:35 2017