Bugs: dmcoords

A list of bugs fixed in CIAO 4.1.2 is available.

Caveats

1. dmcoords does not automatically take into account drifts in the Chandra geometry when calculating sky coordinates.

2. "Target position does not fall on a CCD"

Bugs

1. Incorrect azimuth and off-axis angle for HRC event files

2. dmcoords does not correctly calculate CHIP coordinates on reprojected event files.

Caveats

1. dmcoords does not automatically take into account drifts in the Chandra geometry when calculating sky coordinates.

   These drifts were negligible near the beginning of the mission, but have grown to the order of 10 arcseconds and so cannot be neglected. The Converting between CHIP and SKY Coordinates with dmcoords thread shows how to account for this change.

2. "Target position does not fall on a CCD"

   If you run dmcoords with infile="" and try to set the parameters it needs, e.g.:

   unix% dmcoords infile="" opt=cel ra=<something> dec=<something> \
         detector=ACIS grating="NONE" sim="120 0 -197" \
         ra_nom=<something> dec_nom=<something> roll_nom=<something>
   

   you will see an error of the form: "Target position does not fall on a CCD." Since the tool has been updated to process multi-OBI data, it wants more info and doesn't assume certain things as it did in the past.

   In addition to the shown parameters, you also have to set ra_asp, dec_asp, and roll_asp. If in doubt about the values, set them to the nom parameter value:

   unix% pset dmcoords ra_asp=")ra_nom" dec_asp=")dec_nom" roll_asp=")roll_nom"
   

   This caveat will only affect a small percentage of users, as most run the tool with an infile.

Bugs

1. Incorrect azimuth and off-axis angle for HRC event files

   A keyword was dropped when filtering columns from HRC evt2 files in the pre-CIAO 3.0 data model. This causes dmcoords to not have correct knowledge of the aspect solution; the tool therefore computes an incorrect zero point for the azimuth (phi) and off-axis angle (theta).

   Workaround:

   Use dmstat to get the DETX,DETY values:

   unix% dmstat "evt2[sky=region(reg)][cols det]"
   

   and then use dmcoords to convert these to theta and phi values.

2. dmcoords does not correctly calculate CHIP coordinates on reprojected event files.

   Workaround:

   Since the tool does not explicitly read optical axis information in the header, it assumes that the reprojected RA_NOM and DEC_NOM are the on-axis position and therefore calculates coordinates from the wrong reference point. In order to instruct it to use the original RA_NOM and DEC_NOM, the dmcoords parameters ra_asp and dec_asp should be set to the RA_NOM and DEC_NOM values in the original (unprojected) event file.

   First, retrieve the original RA_NOM and DEC_NOM values:

   unix% set ranom = `dmkeypar evt2.fits ra_nom echo+`
   unix% set decnom = `dmkeypar evt2.fits dec_nom echo+`
   

   Use "echo $ranom" and "echo $decnom" to view the values, if desired. Then set the "asp" coordinates to these values:

   unix% pset dmcoords ra_asp=$ranom dec_asp=$decnom
   

   After setting the other dmcoords parameters, run the tool.

Bugs fixed in CIAO 4.1.2

The following is a list of bugs that were fixed in the CIAO 4.1.2 software release.

1. Incorrect aspect solution produces corrupt error message. (07 Mar 2008)
   (Linux platforms)

   When dmcoords is run with a missing or incorrect aspect solution filename, the error message has junk characters in place of the filename.

   unix% dmcoords infile=acisf01838N002_evt2.fits asolfile=nofile.fits opt=sky x=123 y=123 
   # dmcoords (CIAO 4.1): ERROR: Could not open file ^[%G^[%@le.fits.
   

2. Incorrect exit status when file not found (23 Feb 2009)

   dmcoords exits with "good" status (0) when it can't open a non-existent file. It does correctly report that the file is not found.