Difference between revisions of "Using QL outputs"
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In going from the raw 2D images to the 1D extractions produce by the QL Tool: | In going from the raw 2D images to the 1D extractions produce by the QL Tool: | ||
* The x axis is flipped so that increasing wavelength runs in the same direction as increasing x | * The x axis is flipped so that increasing wavelength runs in the same direction as increasing x | ||
| + | * The spectra are then trimmed to remove overscan, etc. | ||
| + | |||
| + | == For IRAF users == | ||
| + | Since most observers seem to have their own scripts from the old version of the spectrograph, the easiest way to reduce the data is to use the QL wavelength calibrated outputs as a reference for an IRAF reduction of the raw data. | ||
| + | |||
| + | i.e. | ||
| + | * Perform all the pre-processing steps as you would normally on the raw 2D data. | ||
| + | * When you are ready to wavelength calibrate an arc, do so as follows: | ||
| + | ** Use the QL output as a reference. For example, a useful way is to plot the ascii wavelength solution in some interactive plotting window, like python. | ||
| + | ** Then simply, select a few bright, well-spaced lines, hover the cursor over them, and read off the wavelength coordinate. | ||
| + | ** Now, run IRAF - twodspec - identify on the corresponding raw 2D image. Select the same line and input its wavelength as just read off the plot. The solution is good to within a couple of Angstroms, and there are sufficient lines in the arcs that this should work well. | ||
| + | ** Repeat for several lines. | ||
| + | ** When happy, automatically add all the lines (press "l"). | ||
| + | |||
| + | |||
| + | |||
| + | === Advanced notes for users wishing to code up their own routines using these output files === | ||
* The spectra are then trimmed to remove overscan, etc. | * The spectra are then trimmed to remove overscan, etc. | ||
The exact values for these are stored in: | The exact values for these are stored in: | ||
| Line 12: | Line 29: | ||
"badMin1": 2145, <br /> | "badMin1": 2145, <br /> | ||
in python 0-based numbering.<br /> | in python 0-based numbering.<br /> | ||
| + | |||
Revision as of 13:27, 22 December 2016
Contents
Overview
The QL Tool produces quick-look products, but there are some straightforward steps allowing users to use these as a starting point for their science quality reductions
Important Notes
In going from the raw 2D images to the 1D extractions produce by the QL Tool:
- The x axis is flipped so that increasing wavelength runs in the same direction as increasing x
- The spectra are then trimmed to remove overscan, etc.
For IRAF users
Since most observers seem to have their own scripts from the old version of the spectrograph, the easiest way to reduce the data is to use the QL wavelength calibrated outputs as a reference for an IRAF reduction of the raw data.
i.e.
- Perform all the pre-processing steps as you would normally on the raw 2D data.
- When you are ready to wavelength calibrate an arc, do so as follows:
- Use the QL output as a reference. For example, a useful way is to plot the ascii wavelength solution in some interactive plotting window, like python.
- Then simply, select a few bright, well-spaced lines, hover the cursor over them, and read off the wavelength coordinate.
- Now, run IRAF - twodspec - identify on the corresponding raw 2D image. Select the same line and input its wavelength as just read off the plot. The solution is good to within a couple of Angstroms, and there are sufficient lines in the arcs that this should work well.
- Repeat for several lines.
- When happy, automatically add all the lines (press "l").
Advanced notes for users wishing to code up their own routines using these output files
- The spectra are then trimmed to remove overscan, etc.
The exact values for these are stored in:
/usr/local/etc/qlgui/pars.json
"badMax0": 98,
"badMin1": 2145,
in python 0-based numbering.
i.e. in python, to reproduce the same transformation, one would do:
from astropy.io import fits
import numpy as np
im2D = fits.getdata('image.fits')
im2D = np.fliplr(im2D[:,::-1])[:,98:2145]
fits.writeto('outimage.fits',im2D)
This image could then be used for a fresh extraction using IRAF or the user's preffered package, and will be one-to-one pixel aligned with the [approximate] WLC from the 1D extracted arc.
In IRAF, the equivalent would be:
imcopy a0361665[-*,*] test.fits
imcopy test.fits[99:2146,*] out65.fits
[Note the 1-based indexing]
ZZZ interactive WLC examination in IRAF
ZZZ cl script for flipping images and attaching WLC to arcs
