cspice_drdpgr |
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## AbstractCSPICE_DRDPGR computes the Jacobian matrix of the transformation from planetographic to rectangular coordinates. For important details concerning this module's function, please refer to the CSPICE routine drdpgr_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. lon scalar double precision describing the planetographic longitude of the input point. This is the angle between the prime meridian and the meridian containing the input point. For bodies having prograde (aka direct) rotation, the direction of increasing longitude is positive west: from the +X axis of the rectangular coordinate system toward the -Y axis. For bodies having retrograde rotation, the direction of increasing longitude is positive east: from the +X axis toward the +Y axis. The earth, moon, and sun are exceptions: planetographic longitude is measured positive east for these bodies. The default interpretation of longitude by this and the other planetographic coordinate conversion routines can be overridden; see the discussion in Particulars below for details. Longitude is measured in radians. On input, the range of longitude is unrestricted. lat scalar double precision describing the planetographic latitude of the input point. For a point P on the reference spheroid, this is the angle between the XY plane and the outward normal vector at P. For a point P not on the reference spheroid, the planetographic latitude is that of the closest point to P on the spheroid. Latitude is measured in radians. On input, the range of latitude is unrestricted. alt scalar double precision describing the altitude of point above the reference spheroid. Units of `alt' must match those of `re'. 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'. Units of 're' must match those of 'lt'. 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 units of `rp' match those of `re'. the call: ## ExamplesNone. ## ParticularsIt is often convenient to describe the motion of an object in the planetographic coordinate system. However, when performing vector computations it's hard to beat rectangular coordinates. To transform states given with respect to planetographic coordinates to states with respect to rectangular coordinates, one makes use of the Jacobian of the transformation between the two systems. Given a state in planetographic coordinates ( lon, lat, alt, dlon, dlat, dalt ) the velocity in rectangular coordinates is given by the matrix equation: t | t (dx, dy, dz) = jacobi| * (dlon, dlat, dalt) |(lon,lat,alt) This routine computes the matrix | jacobi| |(lon,lat,alt) 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 cspice_dpgrdr ## Required ReadingICY.REQ ## Version-Icy Version 1.0.0, 11-NOV-2013, EDW (JPL) ## Index_EntriesJacobian of rectangular w.r.t. planetographic coordinates |

Wed Apr 5 17:58:00 2017