1. NAME: GETROT
   ; PURPOSE: Return the rotation and plate scale of an image from its FITS header
   ; EXPLANATION:  Derive the counterclockwise rotation angle, and the X and Y scale
   ;     factors of an image, from a FITS image header.   The input parameter
   ;     may be either a FITS image header or an astrometry structure (as
   ;     obtained by extast.pro)

      CALLING SEQUENCE: GETROT, Hdr, [ Rot, CDelt, /SILENT, DEBUG =  ]  or GETROT, Astr, Rot,CDelt...

(Calabretta & Greisen (2002, A&A, 395, 1077) FITs standard))

1.  NAME ADXY
    PURPOSE:Use a FITS header to convert astronomical to pixel coordinates
   ; EXPLANAtion Use an image header to compute X and Y positions, given the RA and Dec (or longitude, latitude) in decimal degrees. 
   ; CALLING SEQUENCE: ADXY, HDR  ;Prompt for Ra and DEC
   ;                   ADXY, hdr, a, d, x, y, [ /PRINT, ALT= ]
2. XYAD
   

         PURPOSE: Use a FITS header to convert pixel (X,Y) to world coordinates
     CALLING SEQUENCE:    XYAD, HDR ;Prompt for X and Y positions ; XYAD, HDR, X, Y, A, D, [ /PRINT, /Galactic, /Celestial, /Ecliptic, ; ALT =, PRECISION=]
     3. ARROW: The ARROW procedure draws one or more vectors with arrow heads.
ARROW, X0, Y0, X1, Y1 [, /DATA | , /NORMALIZED] [, HSIZE=length] [, COLOR=index] [, HTHICK=value] [, /SOLID] [, THICK=value]
Note: you should use the plot first the arrow can work.
EG: plot, X0, YO, psym = 3, symsize =2, xtitle = 'RA(d)', ytitle = 'DEC(d)'
arrow, ........
HSIZE :是关于箭头大小的参数，可设 50-100.

   

3.The ROUND function rounds the argument to its closest integer     Result = ROUND(X [, /L64 ] )

4. CURVEFIT

The CURVEFIT function uses a gradient-expansion algorithm to compute a non-linear least squares fit to a user-supplied function with an arbitrary number of parameters. The user-supplied function may be any non-linear function where the partial derivatives are known or can be approximated. Iterations are performed until the chi square changes by a specified amount, or until a maximum number of iterations have been performed. The CURVEVIT function returns a vector of values for the dependent variables, as fitted by the function fit.

Result = CURVEFIT( X, Y, Weights, A [, Sigma] )

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