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Last modified: 10 October 2007

URL: http://cxc.harvard.edu/ciao3.4/bugs/reproject_image_grid.html
Hardcopy (PDF): A4 | Letter

Bugs: reproject_image_grid


Caveats

  1. Setting the pixelsize to a value in arcseconds

  2. The method parameter: sum vs. average (01 Dec 2006)


Caveats

  1. Setting the pixelsize to a value in arcseconds

    If you are setting the reproject_image_grid pixelsize parameter to a value in arcseconds, you have to specify it when the tool is run, not via pset.

    A feature in the CIAO parameter interface causes double quotes (") to be converted to single quotes (') when they are written to the parameter file:

    unix% pset reproject_image_grid pixelsize='1"' 
    unix% pget reproject_image_grid pixelsize
    1'
    

    Supplying the pixelsize on the command line when the tool is run ensures that the value will be correctly interpreted as arcsec, e.g.

    unix% reproject_image_grid pixelsize='1"' 
    Input image file name (@expmaps.lis): 
    .. etc. ..
    

    The value is also correctly recorded in the history of the output file:

    unix% dmhistory sn1006_expmap.fits reproject_image_grid
    reproject_image_grid infile="@list_of_expmaps.lis" outfile="sn1006_expmap.fits"
    xsize="2500" ysize="2500" xcenter="225.7" ycenter="-41.9" theta="0" pixelsize="1""  
    projection="tan" resolution="1" method="average" coord_sys="world"  
    lookupTab="/soft/ciao/data/dmmerge_header_lookup.txt" clobber="yes" verbose="0" 
    
  2. The method parameter: sum vs. average (01 Dec 2006)

    There has been some confusion over how to set the method parameter when running this tool. Typically users will use sum to reproject the COUNTS image and will use average to reproject the EXPOSURE image when making fluxed images.

    When the method parameter is set to sum, each input image is reprojected to the specified grid using the sum method. If more than one image is input, i.e. a stack of files is given, the combined image is the sum of the individually reprojected files.

    For example, suppose that a 4x4 pixel area in the input corresponds to 1 pixel in the output. Then if the typical input pixel has a value of 1000, the typical output pixel in the intermediate file would have a value of 16000 (the sum of the input pixel values), rather than 1000 (the average of all the input pixel values).

Hardcopy (PDF): A4 | Letter
Last modified: 10 October 2007


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