;+ ;Function: qnorm,q ; ;Purpose: calculate the norm a quaternion or an array of quaternions ; ;Inputs: q: a 4 element array, or an Nx4 element array, representing quaternion(s) ; ;Returns: norm(q): sqrt(a^2+b^2+c^2+d^2) or -1L on fail ; will be a single element or an N length array ; ; ;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 ; ;This implementation of norm does not apply the squareroot sometimes ;applied to a norm. If required the sqrt can easily be applied by the user ; ; ;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 qnorm,q ;this is to avoid mutating the input variable qi = q ;check to make sure input has the correct dimensions qi = qvalidate(qi,'q','qnorm') if(size(qi,/n_dim) eq 0 && qi[0] eq -1) then return,qi ;the actual norm dotp = qdotp(qi, qi) if(size(dotp,/n_dim) eq 0 && dotp[0] eq -1) then begin dprint, 'failed to calculate the dot product of q.q' return, -1L endif out = sqrt(dotp) if(size(q,/n_dim) eq 1) then out = out[0] return,out end