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Basic Information on moment
Task: moment
Purpose: Calculate moments of a Miriad image.
Categories: image analysis
MOMENT calculates the nth moment of a Miriad image. Currently only
the moment of axis 1 or axis 3 is calculated for 3 dimensional images.
To obtain the moments for other axes use the task REORDER to reorder
the axes.
Although by default MOMENT has a somewhat user centric notion of the
moment= keyword, raw moments can be computed in raw mode.
Key: in
The input image. No default.
Key: region
The region of the input image to be used. See documentation for region
on how to specify this. Only the bounding box is supported.
Key: out
The output image. No default.
Key: mom
-3 Velocity at peak, using a 3 point polynomial fit around the peak
-2 Peak temperature (units are same as individual channels)
-1 Average intensity. (units are same as individual channels)
0 Integrated intensity. (e.g. units I x km/s)
1 1st moment = sum(I*v)/sum(I)
2 dispersion = sqrt(sum(I*(v-M1)**2)/sum(I))
The v(i) are the axis values (e.g. velocities). M1 is the first
moment. The moment is calculated independently for each pixel
within the specified clip range. Default = 0.
Note that mom=2 produces a map of sigma ('gaussian' dispersions),
with FWHM = 2*sqrt(2*ln(2)) = 2.355 * sigma if the profile was
a true gaussian.
Key: axis
The axis for which the moment is calculated. Default = 3.
Key: clip
Two values. Exclude pixels with values in the range clip(1) to clip(2).
If only one value is given, then exclude -abs(clip) to abs(clip).
Key: rngmsk
Mask pixels as bad when the 1st moment gives a 1st moment out of
range of that of the axis. This option can only be activated for
mom=1. Default: false
Key: raw
By default, moment is user oriented, i.e. mom=1 computes the velocity.
By setting raw=true, you will get the raw sum(I*v**mom) and will have to use
MATHS to compute back the various maps.
Currently only supported for axis=3.
If the velocity scale is very large and/or mom is large, a rescale
using PUTHD on crval3/cdelt3 may be needed.
Default: false