NAME

aligncal - Calibrate the alignment of a detector

USAGE

aligncal pointsfile=<filename> teldef=<filename> outfile=<filename>

DESCRIPTION

This tool takes a list of observed and expected positions of celestial objects and updates the ALIGNM keywords in a teldef file in order to account for the differences. The positions do not need to be from the same observation.

Warning: this tool modifies the calibration of an instrument, which is not something to be done lightly by the general user.

PARAMETERS

pointsfile [filename]
A FITS file containing a list of observed and expected positions. The positions must be specified in sky coordinates (i.e. pixels) and do not need to be integers. Hidden keywords specify the names of the columns. See below.

outfile [filename]
The name of the modified teldef file which this tool will create. It is permissable to overwrite the input file, but this is not reccomended.

teldef [filename]
Input teldef calibration file describing the instrument coordinate systems. The sky coordinates used in the pointfile must be consistent with the sky coordinates described in this teldef file.

(pointsext = POINTS)[string]
EXTNAME keyword value for the FITS extension containing the observed and expected positions.

(x0_col = X0) [string]
The column containing the observed sky X coordinates

(y0_col = Y0) [string]
The column containing the observed sky Y coordinates

(x1_col = X1) [string]
The column containing the expected sky X coordinates

(y1_col = Y1) [string]
The column containing the expected sky Y coordinates

(weight_col = WEIGHT) [string]
Optional columns containing relative weights to apply to each position when doing the least squares fit. Typically the weights would reflect the accuracy with which the positions are known. If this parameter is set to "NONE" (case insensitive) if if the named columns is not present in the fits file, then all points will receive equal weight.

(tolerance = 0.0001) [real]
The fitting process is iterative. This parameter gives the stopping criterion for the desired RMS accuracy in pixels.

(iterations = 100) [real]
The maximum number of iterations before giving up regardless of whether the RMS accuracy is better than the tolerance parameter.

(decimals = 13) [integer]
Number of decimal places to use when writing the new ALIGNM keyword values.

dec [real]
Declination of center of exposure map [deg].

width [integer]
Width of exposure map [pixels].

height [integer]
Height of exposure map [pixels].

(attdelta = 0.1) [real]
Maximum change in attitude between incrementing the exposure map (radians).

(aberration = yes) [boolean]
Account for velocity aberration?

(chatter = 1) [enumerated integer]
Standard HEAdas chatter parameter.

SEE ALSO

LAST MODIFIED

September 2003