NAME

tevalfit -- Evaluate a transformation on a set of points in an ASCII file.

USAGE

tevalfit input output inpoly entry

DESCRIPTION

This task applies a transformation to a grid of points. The transformation is defined by an entry in a text data base file, and the grid of points is a pair of columns in an ASCII file. The user specifies whether the transformation is to be applied forward (i.e., applying the transformation directly) or backward (i.e., the inverse transformation). The output is written to two columns in an ASCII file. Comments and blank lines in the input file are copied to output.

PARAMETERS

input [file name]

The input ASCII file containing the grid on which the fit described by the inpoly parameter will be evaluated. Blank lines and lines beginning with "#" character are not processed but are copied to output. Inline comments (also beginning with #) are also just copied to output. Each line that is not a comment should contain two values, the X and Y coordinates of the grid point.

output [file name]

The output ASCII file created by tevalfit.

inpoly [file name]

The input transform file, created by the rfitx task or the noao.twodspec.fitcoords task. This is a text data base file.

entry = "respos" [string]

The name of the entry in the transform file inpoly.

(direction = "forwards") [string, Allowed values: forwards | backwards]

The direction of the transformation. The forward transform represents the way that the inpoly file was calculated from the reference file. To develop a backward---or inverse---transform, the program uses a primitive iterative search for points that would be mapped into the points in the input file under the effect of the transform.

EXAMPLES

1. Apply the distortions in entry "f48" in the text data base file stopt.fit to the positions in the ASCII file regular.lis. The output will be written to the ASCII file opt.lis. If stopt.fit contained details of the telescope's optical distortions and regular.lis contained a regularly spaced reseau grid, then the output file opt.lis will show the distortions produced by the Space Telescope's optics on a regular grid in the sky.

   fo> tevalfit regular.lis opt.lis stopt.fit f48

2. Apply the distortions of entry "respos" in the file fitt.fit to the positions in the ASCII file opt.lis. The output should go to a file called final.lis. If the reference grid "opt.lis" contained optical chain distorted points and the input file fitt.fit contained detector distortion, then the output file final.lis will combine optical and detector distortions.

  fo> tevalfit opt.lis final.lis fitt.fit respos

BUGS

The "backwards" option uses a rather primitive algorithm which may not work for unusual cases. In particular, there may be a problem if the transformation involves a large rotation.

REFERENCES

This task was written by Phil Hodge based on revalfitx.

SEE ALSO

rfitx, revalfitx

Type "help focgeom option=sys" for a higher-level description of the focgeom package.