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Last modified: 27 November 2018

URL: http://cxc.harvard.edu/ciao/bugs/celldetect.html

Bugs: celldetect


Table of Contents

Caveats

Bugs


Caveats

RA_ERR and DEC_ERR values near poles

The RA_ERR and DEC_ERR values are approximations and become increasing inaccurate the closer to the poles, DEC=+/-90.

Users may also see incorrect values for these errors for RA values very near 0|360 such that the error bar crosses the boundary and wraps around.

Workaround:

The X_ERR and Y_ERR values in physical pixels is correct. Users can use these together with the known plate scale to compute their own error estimates.


Bugs

Incorrect results using PSF map, psffile, in physical pixel units.

celldetect only knows how to convert a PSF map in arcsec units to logical pixel size to match the input image. All other units are ignored and the PSF map is treated as having logical pixel size values.

If the PSF map was created with physical pixel size values, and the image was binned by any value other than 1, then the PSF map values will not be correctly converted to match the input image. This may result in a different set of source detections and|or may result in the properties of those sources, including the radii, being wrong.

Users can check the units of the PSF map pixel values using dmlist, such as

unix% dmlist mypsfmap.fits cols
--------------------------------------------------------------------------------
Columns for Image Block broad.psfmap
--------------------------------------------------------------------------------
 
ColNo  Name                 Unit        Type             Range
   1   mypsfmap.fits[2613,3222] logical      Real4(2613x3222) -Inf:+Inf            
...

This example shows a PSF map with units of logical pixel size.

Autonaming of ASCII region files uses the .fits extension instead of .reg as would be expected.

In general, autonaming only works for simple cases.