Bugs: reproject_image_grid

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Matching CIAO and CALDB Versions

CIAO 3.4 requires CALDB 3.3.0 or higher to operate properly.

CALDB 3.4.0 and higher should not be used unless you are running CIAO 3.4 or CIAO 4.0.

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News Previous Items

11 Nov 2008

These are the webpages relative to the CIAO 3.4 release (18 December 2006). They are no longer actively updated, however the CXC will continue limited support of CIAO 3.4 for the near future.

CIAO 3.4 users should check the CALDB 3 website for compatible calibration updates.

15 Dec 2008

The newest version of the Chandra Interactive Analysis of Observations software, is CIAO 4.1, released on 15 December 2008. Read the release notes for detailed information. This release requires that CALDB 4.1.0 be installed for the software to work correctly.

Caveats

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"

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).