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Buglog #141
- Wednesday, December 19 1990 @ 11:47 PM GMT
- Contributed by: admin
- Views: 994
MODULE: identify
SYSTEM: V2.9
SYSTEM: V2.9
NUMBER: 141 MODULE: identify SYSTEM: V2.9 DATE: Wed Dec 19 16:47:06 MST 1990 FROM: valdes BUG: The automatic line identification algorithm fails to find some lines in certain circumstances. The source of the problem is when multiple lines in the line list end up being centered in the same place in the data. For example if two lines in the list are 4888.1234 and 4889.1234, the second one is intrinsically weak, and the data is low resolution (say 3A per pixel) then as far as the data is concerned there is just one line. This line will be marked twice with the same position but different wavelengths. The complication is that valid weaker lines will be removed based on the maxfeatures criteria (for example only the 50 highest peak values are kept of which say 10 are multiple assignments to the same peaks in the data). Then after the lines are found the minsep criteria is applied to winnow out the multiple assignments to the same pixel leaving 40 lines found and 10 of the weaker valid lines not found. This is a complex behavior dependent on data resolution, the initial dispersion solution, the line list (the problem occurs with dense line lists used for high resolution such as the thorium list used with lower resolution data), and the maxfeatures and match parameters. STATUS: The bug fix is to winnow out the multiple identifications to the same pixel before selecting the maxfeatures strongest lines. The workaround most likely to work is to reduce the match parameter so that some of the multiple identifications are thrown out based on wavelength differences with the dispersion function estimates. Another thing is to increase maxfeatures but this will result in many undesired weak lines.
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