;+ ;Procedure: rbsp_gse2mgse ; ;Purpose: Transforms from GSE to MGSE (modified GSE coord..defined below) ; ; If W gse is the spin axis unit vector in GSE coordinates, then ; (1) Ymgse = -(Wgse x Zgse) ; ; So Ymgse is now in the spin plane and in the ecliptic plane and duskward. (nearly same as Ygse) ; (2) Zmgse = (Wgse x Ymgse) ; ; So Z mgse points in the spin plane nearly along the positive normal to the ecliptic ; (3) Xmgse= Ymgse x Zmgse ; ; This actually the spin axis of the spacecraft X mgse= W gse ; ; One of the properties of this coordinate system is that if the spin axis points ; towards the sun, then the MGSE system is exactly the same as the GSE system. ; This is a real advantage when thinking about the data and comparing to other instruments. ; ; Second, since on RBSP the spin axis has a large angle relative to the z GSE axis the ; cross product in equation 1 is well defined. None of the cross products involve nearly ; parallel vectors- nothing is ever close to degenerate. ; ; ;Input : tname = the tplot variable with data in GSE coord [n,3] ; wgse = the w-antenna direction in GSE coord. This can either be a [3] element ; array or an [n,3] element array. ; newname = name for output tplot variable. If not set then new name is ; old name + '_mgse' ; ; ;Example: ; rbsp_gse2mgse,'mag_gse',[1,0,0],/nochange ; ;Written by Aaron Breneman, Oct 31, 2012 ; 2013-10-02 -> added a check to make sure the WGSE array is the correct size. ; Returns if it isn't. ;- pro rbsp_gse2mgse,tname,wgse,newname=newname get_data,tname,data=dat,dlimits=dlim,limits=lim zgse = [0,0,1] datx = fltarr(n_elements(dat.x)) daty = datx datz = datx test = size(wgse) ;Loop for single value of wgse. This value will be applied to the rotation of ;every data point if test[0] eq 1 then begin ;Normalize wgse..just in case wgse = wgse/sqrt(wgse[0]^2 + wgse[1]^2 + wgse[2]^2) ;MGSE axes in terms of GSE coord Ymgse = -1*crossp(wgse,zgse) Ymgse = Ymgse/sqrt(Ymgse[0]^2 + Ymgse[1]^2 + Ymgse[2]^2) Zmgse = crossp(wgse,Ymgse) Zmgse = Zmgse/sqrt(Zmgse[0]^2 + Zmgse[1]^2 + Zmgse[2]^2) Xmgse = crossp(Ymgse,Zmgse) Xmgse = Xmgse/(sqrt(Xmgse[0]^2 + Xmgse[1]^2 + Xmgse[2]^2)) for j=0L,n_elements(dat.x)-1 do begin ;Project data along MGSE axes datx[j] = total(dat.y[j,*]*Xmgse) daty[j] = total(dat.y[j,*]*Ymgse) datz[j] = total(dat.y[j,*]*Zmgse) endfor endif if test[0] ne 1 then begin ;Make sure that the Wgse vector has the same number of elements as tname if test[1] ne n_elements(dat.x) then begin print,'****************************************************' print,"'WGSE ARRAY [n,3] DOESN'T HAVE THE CORRECT SIZE....'" print,'THE n MUST BE THE SAME AS THE NUMBER OF TIMES IN TNAME' print,'OR BE SIZE [3] ARRAY' print,'****************************************************' return endif for j=0L,n_elements(dat.x)-1 do begin ;Normalize wgse..just in case wgse[j,*] = wgse[j,*]/sqrt(wgse[j,0]^2 + wgse[j,1]^2 + wgse[j,2]^2) ;MGSE axes in terms of GSE coord Ymgse = -1*crossp(wgse[j,*],zgse) Ymgse = Ymgse/(sqrt(Ymgse[0]^2 + Ymgse[1]^2 + Ymgse[2]^2)) Zmgse = crossp(wgse[j,*],Ymgse) Zmgse = Zmgse/(sqrt(Zmgse[0]^2 + Zmgse[1]^2 + Zmgse[2]^2)) Xmgse = crossp(Ymgse,Zmgse) Xmgse = Xmgse/(sqrt(Xmgse[0]^2 + Xmgse[1]^2 + Xmgse[2]^2)) ;Project data along MGSE axes datx[j] = total(dat.y[j,*]*Xmgse) daty[j] = total(dat.y[j,*]*Ymgse) datz[j] = total(dat.y[j,*]*Zmgse) endfor endif if ~keyword_set(newname) then name = tname+'_mgse' else name = newname store_data,name,data={x:dat.x,y:[[datx],[daty],[datz]]} end