;+ ; NAME: ; COLLDIRS ; ; PURPOSE: ; This procedure determines the viewing direction(s) of one ; of the HEAO A-1 collimators. ; ; CATEGORY: ; HEAO A-1 Geometry. ; ; CALLING SEQUENCE: ; COLLDIRS, Module,RAY,DEY,RAZ,DEZ [,RAc,DECC] ; ; INPUTS: ; Module: Module number of the collimator (1-7), [integer]. ; RAY,DEC: The RA,DEC of the satellite's Y-axis in RADIANS, [float(nbin)]. ; ; OPTIONAL OUTPUTS: ; RAc,DECc: The RA,DEC of the collimator viewing direction, [float(nbin)]. ; ; OPTIONAL KEYWORD OUTPUTS: ; RC: The unit direction vector in spherical coordinates of the ; collimator viewing direction, [float(3,nbin)]. ; ; RESTRICTIONS: ; NOTE: you can also call this routine with scalar input arguments. ; ; EXAMPLE: ; let's choose a RA,DEC near the poles and determine the ; viewing direction for collimator 3. ; ; RA = 75.5*!dtor ; DEC= 89.8*!dtor ; ; COLLDIRS, 3, RA, DEC, RA_M3, DEC_M3, RC=Vec_M3 ; ; MODIFICATION HISTORY: ; Written by: Han Wen, June 1994. ;- pro COLLDIRS, Module,RAY,DEY,RAZ,DEZ, RAc,DECc,RC=Rc M = Module CASE 1 OF (M ge 1) and \$ (M le 4):BEGIN RAc = RAY + !dpi ;-Y axis DECc= -DEY slaCs2c, RAc, DECc, Rc return END (M eq 5):off_ang = (1./3.)*!dtor (M eq 6):off_ang = -(1./3.)*!dtor (M eq 7):BEGIN RAc = RAY DECc= DEY slaCs2c, RAc, DECc, Rc return END ELSE:message,'Invalid module number.' ENDCASE ; Modules 5 and 6 have their viewing directions offset from the ; -Y axis by +/- 1/3 degree. 3 constraints provides 3 equations: ; 1) R # -Y = cos( off_ang ) ; 2) R # Z = sin( off_ang ) ; 3) R # (-Y x Z) = 0 (Axis in same plane) ; which provide the coeff's for a 3 x 3 matrix. Inverting this matrix times ; the vector formed from the scalars of the r.h.s. of these equations ; determines the cartesian coordinates of the module 5/6 scanning directions. ; To vectorize this routine we had to invert this matrix "by hand" instead ; of utilizing IDL's matrix operators. ; Get the -Y axis vector(s): RAneg = RAY + !dpi DECneg= -DEY slaCs2c, RAneg, DECneg, negYs cosO = cos( off_ang ) ;angle from -Y axis lying sinO = sin( off_ang ) ;in the Y-Z plane ; the Z axis and X-axis vector(s): slaCs2c, RAZ, DEZ, Zs slaVxv, Zs, negYs, Xs detA = Xs(0,*) * (negYs(1,*)*Zs(2,*) - negYs(2,*)*Zs(1,*))+\$ Xs(1,*) * (negYs(2,*)*Zs(0,*) - negYs(0,*)*Zs(2,*))+\$ Xs(2,*) * (negYs(0,*)*Zs(1,*) - negYs(1,*)*Zs(0,*)) i_zero = WHERE( detA eq 0, nzero ) if nzero gt 0 then begin print,'ERROR: Determinant of matrix(es) = 0!' print,i_zero return endif A00 = Xs(2,*) *Zs(1,*) - Xs(1,*) *Zs(2,*) ;row 0 A01 = Xs(1,*) *negYs(2,*) - Xs(2,*) *negYs(1,*) ; A02 = negYs(1,*)*Zs(2,*) - negYs(2,*)*Zs(1,*) A10 = Xs(0,*) *Zs(2,*) - Xs(2,*) *Zs(0,*) ;row 1 A11 = Xs(2,*) *negYs(0,*) - Xs(0,*) *negYs(2,*) ; A12 = negYs(2,*)*Zs(0,*) - negYs(0,*)*Zs(2,*) A20 = Xs(1,*) *Zs(0,*) - Xs(0,*) *Zs(1,*) ;row 2 A21 = Xs(0,*) *negYs(1,*) - Xs(1,*) *negYs(0,*) ; A22 = negYs(0,*)*Zs(1,*) - negYs(1,*)*Zs(0,*) A00 = A00/detA A01 = A01/detA ; A02 = A02/detA A10 = A10/detA A11 = A11/detA ; A12 = A12/detA A20 = A20/detA A21 = A21/detA ; A22 = A22/detA n = N_ELEMENTS( RAY ) Rc = fltarr(3,n) Rc(0,*) = A00*cosO + A01*sinO Rc(1,*) = A10*cosO + A11*sinO Rc(2,*) = A20*cosO + A21*sinO slaCc2s, Rc, RAc,DECc end