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smap -- Compute the photocathode mapping function (i.e., the sample direction).
smap input table
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.
- 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).
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
For assistance using this or any other tasks, please contact email@example.com or call the help desk at 410-338-1082.