HELP · SEE_ALSO

## NAME

smap -- Compute the photocathode mapping function (i.e., the sample direction).

## USAGE

`smap input table`

## DESCRIPTION

Using observations of the left and right photocathode mask edges, viewed with the flat field lamp on, a least squares fit is performed to compute the coefficients of the following equation giving sample position as a function of X-deflection and diode number.

S = s0 + (b * dx) + (c * dx * dx) + (e * X)

where dx is the X-deflection minus 2048, X is the diode number and s0, b, and e are the fitted coefficients. The coefficient c is presently not used (i.e., it is set to 0).

The location of the edges are computed by finding the position where the counts equals 1/2(min counts + max counts) about the edge.

At least four edge observations are required; two from the left, and two from the right edge--each of these four edges will have seven bins. A single GHRS observation can have up to seven edge observations stored in different substep bins.

The `smap` task will also compute errors for each of the coefficients.
Because errors between coefficients are correlated, the errors should
not be used to define a error in the mapping function; they
are, however, useful for comparing results with previous calibrations
of the coefficients.

## PARAMETERS

- input [file name template]
- Input observations. All images passed to
`input`must be taken with the same detector at the same Y-deflection. Normally, they will be observations of the edges illuminated by the flat field lamp.

- table = smap [file name]
- The name of the output table containing the sample mapping
coefficients. This table will have the following columns:
'DETECTOR' - Detector being used (integer). 'YDEF' - Y-deflection (double). 'S0' - Sample mapping coefficient (double). 'ERROR_S0' - Error in S0 (double). 'B' - Mapping coefficient (double). 'ERROR_B' - Error in B (double). 'C' - Mapping coefficient (double). 'ERROR_C' - Error in C (double). 'E' - Mapping coefficient (double). 'ERROR_E' - Error in E (double).

## EXAMPLES

1. Compute the sample coefficients using observation images
`data1`, `data2`, `data3`, and `data4`. The results are placed in table
`sampcoef`.

hr> smap data1[*],data2[*],data3[*],data4[*] sampcoef

## 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.