- Form:POLY source ORD=n [SUB] [DIV] [LOAD] [NOZERO]
[SILENT]
-
- source
- is the number of the spectrum to fit,
- ORD=
- is the order of the polynomial to fit (<7),
- SUB
- subtracts the polynomial from the data,
- DIV
- divides the polynomial by the data,
- LOAD
- loads the VISTA variables COEFF0, COEFF1, ...,
COEFFn with the coefficients of the fit, and
DCOEFF0, DCOEFF1,..., with their estimated error.
- NOZERO
- ignore pixels with value= 0 in the fit
- SILENT
- suppresses terminal output
POLY fits a polynomial to the spectrum in image buffer 'source'. The order
of the polynomial is specified by the keyword 'ORD=n', where n=1 is a line,
n=2 is a quadratic, and so forth. Here a ``spectrum'' is any 1-D image
vector (an ``image'' with 1 row and NC columns).
As in the SPLINE command the keywords SUB and DIV can be used to tell the
program to subtract or divide (respectively) the original spectrum by the
fit. (Without both of these keywords the spectrum will be replaced by the
fit.) As in the SURFACE command the keyword LOAD will load VISTA variables
with the computed polynomial coefficients, so that they are accessible by
other commands. The names of the variables loaded are COEFF0, COEFF1, ...,
COEFFn, where 'n' is again the order of the fit. The formula using these
coefficients is
y = COEFF0 + COEFF1 * x + COEFF2 * x * x + ...
where y is the intensity and x is the pixel number.
Examples:
- POLY 14 ORD=3
- Fits a cubic polynomial to the spectrum in buffer
14. The spectrum is replaced by the polynomial fit.
- POLY 3 ORD=2 SUB
- Buffer 3 is fit with a parabola, which is then
subtracted from the original data.
- POLY 5 ORD=3 LOAD
- Buffer 5 is fit with a third-order (cubic)
polynomial which then replaces the original data in the buffer. The
four VISTA variables COEFF0, COEFF1, COEFF2, and COEFF3 are loaded
with the fit coefficients, and variables DCOEFF0, DCOEFF1, DCOEFF2,
and DCOEFF3 with the fit coefficient errors.