;+ ;Function: qmult,q1,q2 ; ;Purpose: multiply two quaternions or two arrays of quaternions ; ;Inputs: q1: a 4 element array, or an Nx4 element array, representing quaternion(s) ; q2: a 4 element array, or an Nx4 element array, representing quaternion(s) ; ;Returns: q1*q2, or -1 on failure ; ;;Notes: Implementation largely copied from the euve c library for ;quaternions ;Represention has q[0] = scalar component ; q[1] = vector x ; q[2] = vector y ; q[3] = vector z ; ;The vector component of the quaternion can also be thought of as ;an eigenvalue of the rotation the quaterion performs ; ; ;Written by: Patrick Cruce(pcruce@igpp.ucla.edu) ; ; $LastChangedBy: pcruce $ ; $LastChangedDate: 2007-11-11 17:12:08 -0800 (Sun, 11 Nov 2007) $ ; $LastChangedRevision: 2027 $ ; $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/cotrans/cotrans.pro $ ;- function qmult,q1,q2 compile_opt idl2 ;this is to avoid mutating the input variables q1i = q1 q2i = q2 if(size(/n_dim,q1i) ne size(/n_dim,q2i)) then begin dprint,'Number of dimensions in quaternion q1 and quaternion q2 do not match' return,-1 endif ;check to make sure input has the correct dimensions q1i = qvalidate(q1i,'q1','qmult') q2i = qvalidate(q2i,'q2','qmult') if(size(q1i,/n_dim) eq 0 && q1i[0] eq -1) then return,q1i if(size(q2i,/n_dim) eq 0 && q2i[0] eq -1) then return,q2i ;make sure elements match if(n_elements(q1i) ne n_elements(q2i)) then begin dprint,'Number of elements in quaternion q1 and quaternion q2 do not match' return,-1 endif ;now the actual dirty work qtmp0 = q1i[*,0]*q2i[*,0] - q1i[*,1]*q2i[*,1] - q1i[*,2]*q2i[*,2] - q1i[*,3]*q2i[*,3] qtmp1 = q1i[*,1]*q2i[*,0] + q1i[*,0]*q2i[*,1] - q1i[*,3]*q2i[*,2] + q1i[*,2]*q2i[*,3] qtmp2 = q1i[*,2]*q2i[*,0] + q1i[*,3]*q2i[*,1] + q1i[*,0]*q2i[*,2] - q1i[*,1]*q2i[*,3] qtmp3 = q1i[*,3]*q2i[*,0] - q1i[*,2]*q2i[*,1] + q1i[*,1]*q2i[*,2] + q1i[*,0]*q2i[*,3] qout = [[qtmp0],[qtmp1],[qtmp2],[qtmp3]] return,reform(qout) end