;++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
;
;*NAME:                  grating
;
;*CATEGORY:              instrumentation tool
;
;*PURPOSE:               compute parameters of grating spectrograph
;
;*CALLING SEQUENCE:      grating, lpmm, blz, alpha,npix,m, $
;                                 pix, lambda, lmin,lcen,lmax, $ 
;                                 disp, rdisp, dlam, R [,optional Keywords] 
;*PARAMETERS: 
;              input:    lpmm    groove density [lines per mm]
;                        blz     blaze angle [degrees]
;                        alpha   angle grating normal to incident beam
;                        npix    number of pixels on CCD (dispersion)
;                        m       spectral order Note: -1 is FORWARD diffraction
;
;              output:   pix     array of npix values: pixel number
;                        lam     array of npix corresponding Lambda values [A]
;                        lmin    lambda_min, minimum wavelength [A]
;                        lcen    lambda_cen, central wavelength [A]
;                        lmax    lambda_max, maximum wavelength [A]
;                        rdisp   reciprocal linear dispersion [A/mm]
;                        pdisp   reciprocal linear dispersion [A/pix]
;                        dlam    spectral resolution [A]
;                        R       resolving power Lambda/d_Lambda
;
;   optional Keywords:   ETA     (collimator,camera) angle [degrees], def. 42 degr.
;                        INFO    Flag, /INFO prints results on screen
;                        VIEW    Flag, /VIEW plots Lambda and Grating Geometry
;                        PIXSIZE Pixel Size, default = 0.015mm
;                        PSF     Width of instrumental profile [pix], def.=4.0
;                        FLIP    flag, /FLIP reverses order of pixels
;                        GROTPOS flag, /GR : alpha is Grating Rotator Encoder position
;                        FLEN    Focal Length [mm], different from default f=270mm
;
;*EXAMPLES:               grating, 1200,17.5,2,2048,1, pix,lam,lmin,lcen,lmax,
;                                  ldisp,rdisp,dlam,R,/V,/I,/FLIP 
;
;                         grating, 1200,17.5,-48,2048,1,pix,lam,lmin,lcen,lmax,
;                                  ld,rd,dl,r,/v,/i,/FLIP,/GR
;
;*SYSTEM VARIABLES USED:
;
;*COMMON BLOCKS:
;
;*INTERACTIVE INPUT:
;
;*SUBROUTINES CALLED:     grat_plot
;
;*FILES USED:
;
;*SIDE EFFECTS:
;
;*RESTRICTIONS:
;
;*NOTES:
;
;*PROCEDURE:
;
;*MODIFICATION HISTORY:
grating_VERSION = 'grating.pro Version 1.0 --- 27/05/02 mmr'
;
;	27/05/02	MMR	initial programming
;          
;*AUTHORS:
;
;	MMR		Martin M. Roth	Astrophysikalisches Institut Potsdam
;					An der Sternwarte 16
;					D-14547 Potsdam  
;					Tel. +49 - 331 - 7499 313
;                                       email: mmroth@aip.de
;-