cspice_ducrss |
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## AbstractCSPICE_DUCRSS calculates the unit vector parallel to the cross product of the position components of two state vectors and the time derivative of this unit vector. For important details concerning this module's function, please refer to the CSPICE routine ducrss_c. ## I/OGiven: s1 a double precision 6-vector defining a state; s1 = (r1, dr1 ). -- dt s2 a second state vector; s2 = (r2, dr2 ). -- dt An implicit assumption exists that both states lie in the same reference frame. If this is not the case, the numerical result has no meaning. the call: ## 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. One can construct non-inertial coordinate frames from apparent positions of objects or defined directions. However, if one wants to convert states in this non-inertial frame to states in an inertial reference frame, the derivatives of the axes of the non-inertial frame are required. Define a reference frame with the apparent direction of the sun as seen from earth as the primary axis (x). Use the earth pole vector to define with the primary axis a primary plane of the frame. ;; ;; Load SPK, PCK, and LSK kernels, use a meta kernel for convenience. ;; cspice_furnsh, 'standard.tm' ;; ;; Define the earth body-fixed pole vector (z). The pole ;; has no velocity in the earth fixed frame "IAU_EARTH." ;; z_earth = [ 0.D, 0, 1, 0, 0, 0 ]; ;; ;; Calculate the state transformation between IAU_EARTH and J2000 ;; at an arbitrary epoch. ;; utc = 'Jan 1, 2009' cspice_str2et, utc, et cspice_sxform, 'IAU_EARTH', 'J2000', et, trans ;; ;; Transform the earth pole vector from the IAU_EARTH frame to J2000. ;; z_j2000 = transpose(trans) # z_earth ;; ;; Calculate the apparent state of the sun from earth at the epoch ;; 'et' in the J2000 frame. ;; target = 'Sun' observer = 'Earth' cspice_spkezr, target, et, 'J2000', 'LT+S', observer, state, ltime ;; ;; Define the z axis of the new frame as the cross product between ;; the apparent direction of the sun and the earth pole. 'z_new' cross ;; 'x_new' defines the y axis of the derived frame. ;; cspice_dvhat, state, x_new ## ParticularsThe frame transformation described in the Example may also be implemented using a dynamic frames kernel. ## Required ReadingFRAMES.REQ ICY.REQ ## Version-Icy Version 1.0.1, 09-MAY-2016, EDW (JPL) Eliminated typo in example code; no change to functionality. -Icy Version 1.0.0, 20-APR-2010, EDW (JPL) ## Index_Entriescompute a unit cross product and its derivative |

Wed Apr 5 17:58:00 2017