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`lsmooth(`

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

Returns a directionally smoothed version of

.
`image`

and `vx`

contain the two coordinates of the
direction at each point. The direction of the stream vector is the
direction of the streamline through the point, or, if `vy``/straight`

is specified, a weighted average or total of data points on the straight
line which is tangential to the streamline through that point. For each
point, its data value is spread across data points on 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 target 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 target interval extends in both directions from the starting
point (determined by the direction of the stream vector and the exactly
opposite direction).

By default (or if `/boxcar`

is specified), the spreading 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 spreading is
gaussian instead, with the length of the stream vector indicating the
FWHM of the gaussian kernel.

By default, a value that is spread to a particular data element is
multiplied by the length of the segment of the streamline or straight
line that falls within the data element, and by a gaussian weight (if
`/gaussian`

was selected), but is not normalized to take into
account the smoothing width. If `/normalize`

is specified, then
the spread values are normalized with the smoothing width, too, so that
the total of the smoothed data equals the total of the unsmoothed data
(except for edge effects).

`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: dsmooth, esmooth, gsmooth, smooth

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