- Form: FINDSHIFT s1 s2 [RAD=r] [SHIFT=s] [XS=i] [XE=j]
[ROW=k] [LOAD] [SILENT]
-
- RAD=R
- Search Radius for the Chi-squared minimum.
The default is 1/4 of the number of columns.
- SHIFT=
- A guess of SHIFT, i.e. the column shift on the
second spectrum required to match the template.
- XS=I
- First column, on template, of the spectral
region for Chi-squared computation.
- XE=J
- Last column of the selected region.
- ROW=k
- Estimate shift in row k (when images are given).
- LOAD
- Loads variables SHIFT, DSHIFT, and SHIFTVAR with
the relative shift, an estimation of its error
and the unbiased mean variance of the spectra.
- SILENT
- Loads variables but does not print results.
FINDSHIFT computes the relative shift between two spectra. Given two
spectra (1 row images), it computes SHIFT, the number pixels that the
second (shifted) spectrum would have to be shifted to match (in the least
squared sense) the first (template) spectrum. The user can selected a
spectral region for the chi-squared computation. The algorithm solves the
interpolation problem, so the command provides accurate fractional shifts.
Since the algorithm minimizes the difference in counts, results are more
accurate if the spectra are normalized to have the same number of counts
within the spectral region of interest. The algorithm looses sense if the
spectra are very different.
If two images are given (more than one row), a single row will be
considered for the shift calculation, the template's starting row is the
default row, but can be changed with the 'ROW=' keyword.