cspice_dpgrdr |
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## AbstractCSPICE_DPGRDR computes the Jacobian matrix of the transformation from rectangular to planetographic coordinates. For important details concerning this module's function, please refer to the CSPICE routine dpgrdr_c. ## I/OGiven: body the scalar string name of the body with which the planetographic coordinate system is associated. `body' is used by this routine to look up from the kernel pool the prime meridian rate coefficient giving the body's spin sense. x y, z scalar double precision describing the rectangular coordinates of the point at which the Jacobian of the map from rectangular to planetographic coordinates is desired. re scalar double precision describing the equatorial radius of a reference spheroid. This spheroid is a volume of revolution: its horizontal cross sections are circular. The shape of the spheroid is defined by an equatorial radius 're' and a polar radius 'rp'. f scalar double precision describing the flattening coefficient f = (re-rp) / re where rp is the polar radius of the spheroid. (More importantly rp = re*(1-f).) the call: ## ExamplesNone. ## ParticularsWhen performing vector calculations with velocities it is usually most convenient to work in rectangular coordinates. However, once the vector manipulations have been performed, it is often desirable to convert the rectangular representations into planetographic coordinates to gain insights about phenomena in this coordinate frame. To transform rectangular velocities to derivatives of coordinates in a planetographic system, one uses the Jacobian of the transformation between the two systems. Given a state in rectangular coordinates ( x, y, z, dx, dy, dz ) the velocity in planetographic coordinates is given by the matrix equation: t | t (dlon, dlat, dalt) = jacobi| * (dx, dy, dz) |(x,y,z) This routine computes the matrix | jacobi| |(x, y, z) The planetographic definition of latitude is identical to the planetodetic (also called "geodetic" in SPICE documentation) definition. In the planetographic coordinate system, latitude is defined using a reference spheroid. The spheroid is characterized by an equatorial radius and a polar radius. For a point P on the spheroid, latitude is defined as the angle between the X-Y plane and the outward surface normal at P. For a point P off the spheroid, latitude is defined as the latitude of the nearest point to P on the spheroid. Note if P is an interior point, for example, if P is at the center of the spheroid, there may not be a unique nearest point to P. In the planetographic coordinate system, longitude is defined using the spin sense of the body. Longitude is positive to the west if the spin is prograde and positive to the east if the spin is retrograde. The spin sense is given by the sign of the first degree term of the time-dependent polynomial for the body's prime meridian Euler angle "W": the spin is retrograde if this term is negative and prograde otherwise. For the sun, planets, most natural satellites, and selected asteroids, the polynomial expression for W may be found in a SPICE PCK kernel. The earth, moon, and sun are exceptions: planetographic longitude is measured positive east for these bodies. If you wish to override the default sense of positive longitude for a particular body, you can do so by defining the kernel variable BODY<body ID>_PGR_POSITIVE_LON where <body ID> represents the NAIF ID code of the body. This variable may be assigned either of the values 'WEST' 'EAST' For example, you can have this routine treat the longitude of the earth as increasing to the west using the kernel variable assignment BODY399_PGR_POSITIVE_LON = 'WEST' Normally such assignments are made by placing them in a text kernel and loading that kernel via cspice_furnsh. The definition of this kernel variable controls the behavior of the CSPICE planetographic routines cspice_pgrrec cspice_recpgr ## Required ReadingICY.REQ ## Version-Icy Version 1.0.0, 11-NOV-2013, EDW (JPL) ## Index_EntriesJacobian of planetographic w.r.t. rectangular coordinates |

Wed Apr 5 17:58:00 2017