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## NAME

lmap -- Compute the photocathode mapping function (i.e., the line direction).

## USAGE

`lmap input table `

## DESCRIPTION

Determine the Y-deflections needed to center the edges on the main diode array
using observations of the upper and lower photocathode mask edge with
the flat field lamp on. Edge positions are determined
by constructing an edge profile as a function of Y-deflection by summing the
diodes in the range `dfirst` to `dlast` for each Y-deflection. The
edge is then computed as the Y-deflection where the summed counts
is equal to the average of the minimum and maximum counts for the edge.
This process is done for both the upper and lower edge.

The coefficients in the following equation are computed, assuming the line position of the upper edge is 0 and the lower edge is 430.

L = L0 + A * dy where: dy - Y-deflection minus 2048, L - line position, and L0 and A - mapping coefficients.

## PARAMETERS

- input [file name template]
- Names of the images containing observations of the upper and lower
photocathode mask edges. These images must all be for the same detector
and should have a length of 500 data points (the size of the GHRS
raw data image). All observations must have the same exposure time--otherwise
they must be normalized before running the
`lmap`task.

- table = "lmap" [file name]
- Name of the output table containing the mapping coefficients.
This table will have one row with the following columns (although
the
`ERROR_LO`and`ERROR_A`columns are not used by this task):'DETECTOR' - Detector number (integer). 'YDEF' - Y-deflection (integer). 'L0' - Mapping coefficient (double). 'ERROR_L0' - Error in 'L0', set to 0.0 (double). 'A' - Mapping coefficient (double). 'ERROR_A' - Error in 'A', set to 0.0 (double).

Note that the

`ERROR_L0`and`ERROR_A`columns are required by RSDP, but are not used.

- (dfirst=101) [integer, min=1, max=500]
- First diode in the range of diodes that are to be summed for each Y-deflection.

- (dlast=401) [integer, min=1, max=500]
- Last diode in the range of diodes to be summed for each Y-deflection.

## EXAMPLES

1. Compute the mapping coefficients using
observations in the input images, `data1`, `data2`, `data3`, and `data4`.
The results
are to be placed in the table `lincoef`.

hr> lmap data1[*],data2[*],data3[*],data4[*] lincoef

## BUGS

## REFERENCES

## HELP

For assistance using this or any other tasks, please contact help@stsci.edu or call the help desk at 410-338-1082.