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.

SEE ALSO

smap