;+ ;Procedure: sse_crib.pro ; ;Purpose: A crib showing how to transform data from GSE to SSE coordinate system. ; SSE is defined as: ; X: Moon->Sun Line projected into the ecliptic plane ; Y: Z x X ; Z: Ecliptic north ; ;Notes: ; ; Code heavily based on make_mat_Rxy.pro & transform_gsm_to_rxy.pro by Christine Gabrielse(cgabrielse@ucla.edu) ; ; $LastChangedBy: pcruce $ ; $LastChangedDate: 2013-09-19 10:56:58 -0700 (Thu, 19 Sep 2013) $ ; $LastChangedRevision: 13080 $ ; $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/spdsoft/trunk/projects/themis/examples/advanced/thm_crib_sse.pro $ ;- probe = 'a' timespan,'2008-03-23' thm_load_slp cotrans,'slp_sun_pos','slp_sun_pos_gse',/gei2gse cotrans,'slp_lun_pos','slp_lun_pos_gse',/gei2gse sse_matrix_make,'slp_sun_pos_gse','slp_lun_pos_gse',newname='sse_mat' ;load fgm data to be transformed thm_load_fgm,probe=probe,coord='gse' ;---------------------------------------------- ;simple rotation ;because fgm data is not specified relative to the coordinate system's frame of reference ;transformation is rotational only tvector_rotate,'sse_mat','th'+probe+'_fgl_gse' tplot,['th'+probe+'_fgl_gse','th'+probe+'_fgl_gse_rot'] ;---------------------------------------------- ;---------------------------------------------- ;inverse rotation tvector_rotate,'sse_mat','th'+probe+'_fgl_gse_rot',newname='th'+probe+'_fgl_gse_inv',/invert tplot,['th'+probe+'_fgl_gse','th'+probe+'_fgl_gse_inv','th'+probe+'_fgl_gse_rot'] ;---------------------------------------------- ;load state data to be transformed thm_load_state,probe=probe cotrans,'th'+probe+'_state_pos','th'+probe+'_state_pos',/gei2gse ;---------------------------------------------- ;position transformation ;position is trickier, because it is measured with respect to coordinate center ;We need to perform an affine transformation which we do in 3 steps. ;first interpolate the moon position onto state position tinterpol_mxn,'slp_lun_pos_gse','th'+probe+'_state_pos' ;next subtract the moon position from the state position to account for relative position of coordinate frames calc,'"th'+probe+'_state_pos_sub"="th'+probe+'_state_pos"-"slp_lun_pos_gse_interp"',/verbose ;last perform the rotational component of the transformation. tvector_rotate,'sse_mat','th'+probe+'_state_pos_sub',newname='th'+probe+'_state_pos_sse' ;---------------------------------------------- ;velocity transformation ;velocity is even trickier, because the coordinate systems are in motion themselves. ;first generate spacecraft velocity in gse coordinates. ;Cotrans cannot properly account for relative velocity of coordinate systems ;when transforming, thus this is best done with derivative not cotrans or thm_cotrans. deriv_data,'th'+probe+'_state_pos',newname='th'+probe+'_state_vel' ;second generate the lunar velocity in gse coordinates by ;taking the derivative of the lunar position in gse coordinates deriv_data,'slp_lun_pos_gse',newname='slp_lun_vel_gse' ;third interpolate lunar velocity onto state velocity tinterpol_mxn,'slp_lun_vel_gse','th'+probe+'_state_vel' ;next subtract moon velocity from the state velocity to account for relative motion of coordinate frames calc,'"th'+probe+'_state_vel_sub"="th'+probe+'_state_vel"-"slp_lun_vel_gse_interp"',/verbose ;finally rotate the data into the new coordinate system tvector_rotate,'sse_mat','th'+probe+'_state_vel_sub',newname='th'+probe+'_state_vel_sse' ;---------------------------------------------- ;---------------------------------------------- ;inverse velocity transformation ;just do the transformation backwards. First invert rotation, then invert offset tvector_rotate,'sse_mat','th'+probe+'_state_vel_sse',newname='th'+probe+'_state_vel_sub_inv',/invert calc,'"th'+probe+'_state_vel_sse_inv"="th'+probe+'_state_vel_sub_inv"+"slp_lun_vel_gse_interp"',/verbose ;Note: ; 1. This same affine transformation can be done for accelerations, by taking an additional ;derivative ; 2. Taking discrete derivatives will lead to approximation errors on the edges of the time series end