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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.  The
        spectral axis, which is determined automatically, must be on
        axis 1, 2, or 3.  Moments may be computed for other axis types
        by specifying the axis number, though the brightness units
        recorded in the output image header will likely not be correct.
        They can be fixed using PUTHD.

Key: in
        The input image.  No default.

Key: region
        Region of the input image to be used, only the bounding box is
        supported.  See documentation for region on how to specify this.

Key: out
        The output image.  No default.

Key: mom
        -3: Velocity at peak intensity using a three-point quadratic fit
            around the peak (km/s).
        -2: Peak intensity using a three-point quadratic fit (units same
            as individual channels).
        -1: Average intensity (units same as individual channels).
         0: 0th moment = sum(I) (integrated intensity, I x km/s).
         1: 1st moment = sum(I*v)/sum(I), (velocity centroid, km/s),
                         where v is the velocity.
         2: 2nd moment = sqrt(sum(I*(v-M1)**2)/sum(I)), (velocity
                         dispersion, km/s), where M1 is the first
                         moment.  If the line profile is Gaussian,
                         this produces a map of Gaussian sigma, and
                         FWHM = 2*sqrt(2*ln(2))*sigma = 2.355*sigma.
 
            The moments are calculated independently for each pixel
            using spectral channels with intensity satisfying the
            specified clip range.
 
            For frequency axes the radio velocity is computed from the
            line rest frequency recorded in the header.  For velocity
            axes the axis scale is used directly.

Key: axis
        Axis for which the moment is calculated.  Moments may be
        computed for non-spectral axes though brightness units recorded
        in the output image header will usually be incorrect.  Defaults
        to the spectral axis determined from the input image header.

Key: clip
        Two values.  For mom >= -1, exclude spectral channels with
        intensity in the range clip(1) to clip(2) inclusive.  If only
        one value is given, then exclude -abs(clip) to +abs(clip).
        Default = 0 which excludes nothing.

Key: span
        For mom >= -1, exclude channels further than the specified
        number of channels from the peak, hence using a total of
        2*span + 1 channels to compute the moment.  If the peak is too
        close to the first or last channel to allow the full span, then
        the pixel will be blanked in the output map.  Please bear this
        in mind when specifying the channel range (via 'region').
        Default = 0 which means no restriction.

Key: rngmsk
        For mom > 0, mask pixels in the output map when the 1st moment
        lies outside the range of the spectral axis.  This can happen
        because sum(I) can be arbitrarily small in emission-free
        channels but with sum(I*v) non-vanishing.  Default: false.

Key: pkmask
        Two values.  For mom = -3, 1, and 2 (velocities) mask pixels in
        the output map for which the peak intensity lies within the
        range pkmask(1) to pkmask(2) exclusive.  If only one value is
        given, then mask pixels with peak intensity less than pkmask.
        Default = 0.
 
Revision: 1.17, 2011/10/25 09:43:44 UTC

Generated by miriad@atnf.csiro.au on 21 Jun 2016