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resample stsdas.hst_calib.ctools


NAME · USAGE · DESCRIPTION · PARAMETERS · EXAMPLES · BUGS · SEE_ALSO

NAME

resample -- Resample calibrated spectra to a linear wavelength scale.

USAGE

resample input output

DESCRIPTION

The input spectra are resampled to match the dispersion parameters given by the user: starting wavelength, wavelength increment, ending wavelength, and spectrum length. The output spectra pixel intervals may be either in wavelength or in the logarithm of the wavelength. The output spectrum may be zero-filled on either or both ends if the choice of parameters requires extrapolation beyond the limits of the input spectrum.

The image names of the spectra to be resampled need not have an extension of .c1h. However, if a separate wavelength image is not specified, the task will assume that there exists a corresponding wavelength image with the same root as the flux image and an extension of .c0h, and placed in the same directory as the flux image.

The wavelength images should contain monotonically increasing (or decreasing) values. If the input wavelength images happen to be zero-padded, use the image section specification to pass only the valid part of the spectrum to this task.

If all groups of a multigroup image are to be processed, the image name should be given without a group designation. To process a single group of a multigroup image, give the image name with a group designation (e.g., "z00xh903r.c1h[5]", to resample the fifth group of the image).

The Hanning window used with the sinc function is defined as:

	wj = 1 / 2 [1 - cos(2 * PI * (j - 1) / (N - 1))] 
	 
	where j goes from 1 to N, the size of the window.

Except for the sinc function, the interpolation algorithms are the same as those in the IRAF task dispcor.

PARAMETERS

input [file name template]
The image names of the spectra to be resampled.
output [file name template]
The image names of the new spectra.
(wave = "") [file name template]
The names of the wavelength images corresponding to the input spectra.
(logarithm = no) [boolean]
Should the output spectra be linear in the logarithm base 10 of wavelength?

If set to "no" the output spectra will be linear in the wavelength.

(pixout = 0) [integer]
Length of the output spectrum.

If 0, then the output spectrum will be the same size as the input spectrum. If INDEF, then the size of the output spectrum will be whatever is required to satisfy the requirements specified by the wave0, delwav, and ewave parameters.

(wave= INDEF) [real]
Starting wavelength.

If INDEF, then the first wavelength of the input spectrum is used. If a value is specified, the output spectra will be resampled so that the first pixel has this wavelength. If a logarithmic scale is specified then this number must be the logarithm of the starting wavelength.

(delwav = INDEF) [real]
The output spectra will be resampled having a pixel-to-pixel increment specified by delwav. If a logarithmic scale is specified then this number is the interval in the logarithm of the wavelength. If INDEF, then this is calculated based on the starting, ending, and size of the output spectrum.
(ewave = INDEF) [real]
The ending output wavelength. If INDEF, then the last usable wavelength of the input is used.
(interp_mode = "linear") [string]
Allowed values: linear | spline3 | poly3 | poly5 | sums | sinc

Interpolation method used in resampling.

The interpolation may be linear, cubic spline ("spline3"), third order polynomial ("poly3"), or fifth order polynomial ("poly5"). The count preserving interpolator option ("sums") may be specified. Additionally, a sinc function interpolation may be selected. The "sinc" option uses a Hanning window; the size of the window is selected by the user in the parameter window.

(window = 35) [integer]
This parameter must be present if interp_mode is set to "sinc", otherwise it is not used. This parameter specifies the size of the Hanning window which is convolved with the sinc function.

EXAMPLES

1. Resample all groups of the observation z00xh903r to a linear wavelength scale covering the same wavelength range using a sinc function interpolation with a window 15 pixels wide.

  hr> resample z00xh903r.c1h new903.c1h interp=sinc window=15

2. Resample the second group of the observation z00xh903r to a linear wavelength scale spanning 1000 pixels starting at 2695 angstroms and using a wavelength per pixel value of .01 angstroms. Interpolate using a fifth order polynomial.


  hr> resample z00xh903r.c1h[2] x903.c1h wave0=2695. delwav=0.001 \
  >>> pixout = 1000 interp=poly5

3. Resample and flip a red-side FOS spectrum y00hf104t to a linear wavelength scale.

  fo> resample y00hf104t.c1h newfos.c1h wave0=3250 delwav=0.75

4. An alternate way to flip a red-side FOS spectrum while letting the task determine the scaling would be:

  fo> resample y00hf104t.c1h newfos.c1h wave=y00hf104t.c0h

5. Resample a part of an FOS observation:

  fo> resample ytest.c1h[200:400] ytestprime.c1h 

6. Resample an HRS observation to a high dispersion and create the spectrum large enough to span the specified wavelength region.

  hr> resample z00hf104t.c1h high.hhh pixout=indef wave0=965.3
  >>> delwave=.001 ewave=1843.2

BUGS

SEE ALSO

dispcor


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