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`dsmooth(`

`image`, `vx`, `vy` [, /boxcar, /gaussian,
/onesided, /twosided, /total, /straight])

Returns a directionally smoothed version of

.
`image`

and `vx`

contain the two coordinates of the
`vy`*stream vector* at each point. The direction of the stream vector
is the direction of the streamline through the point. For each point, a
weighted average or total is returned of data points on the streamline
through that point, or, if `/straight`

is specified, a weighted
average or total of data points on the straight line which is tangential
to the streamline through that point. The smoothing width is taken from
the length of the stream vector.

By default, or if `/onesided`

is selected, then the smoothing
interval extends, for each point, to only one side of that point
(determined by the direction of the stream vector). If `/twosided`

is selected, then the smoothing interval extends in both directions from
the starting point (determined by the direction of the stream vector and
the exactly opposite direction).

Only the smoothing width at the point for which the weighted average is
determined matters to the result at that point. By default (or if
`/boxcar`

is specified), the smoothing is of the boxcar type, and
the total length of the boxcar is equal to the length of the stream
vector (if `/twosided`

is specified or implied), or to one half of
the length of the stream vector (if `/onesided`

is specified). If
`/gaussian`

is specified, then the smoothing is gaussian instead,
with the length of the stream vector indicating the FWHM of the gaussian
kernel.

By default, weighted averages are returned. If `/total`

is
specified, then weighted totals are returned instead.

`lsmooth`

is very similar to `dsmooth`

, except that in
`lsmooth`

a particular source value is spread along its associated
streamline (or tangent), whereas in `dsmooth`

a particular target
value is constructed from source values taken from its associated
streamline (or tangent).

See also: esmooth, gsmooth, lsmooth, smooth

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