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Each of the smaller fragments is merged with the neighbouring plot with which it shares the
longest boundary, provided this does not involve crossing a barrier.
Thenalbarrier-relatedparameter is a tolerance thatdenes thedistance from the edge of
the plotthat barrier polygons or lines can be ignored. This parameter is needed because, with
certain data formats, there can be very small movements of vertices following the splitting
procedure (as a result of coordinate precision). Usually this is only a few centimetres and
is negligible, but does create a problem when resolving merges of adjacent plot polygons.
The default tolerance is 1, and the units for this tolerance are the coordinate system units
(e.g. meters for UTM). If you use a barrier line dataset that contains overshoots, then you
may need to increase this tolerance to allow the merging algorithm to resolve acceptable
merges. It is particularly important when using a barrier line dataset that 1) lines that are
supposed to cross do actually cross (e.g. roads at a T junction), and 2) that overshoots at
such crossings are not too long. The former issue results in plots that fail to be split by a
barrier line, while the latter issue can result in a failure of the algorithm to deal with plot
fragments.
Syntax
genregionsampleplots(extent, out, dim, [outzones], [dimzones], [snap], [raster], [barrierpoly],
[barrierline], [minarea], [tol]);
extent
the reference layer that denes the extent of the vector grid, or a set of
four values that dene the extent (min x, max x, min y, max y)
out
the output polygon data source for the plots
dim
the dimensions of the plots in coordinate system units, e.g. 100 or
c(100,200); specifying one value results in square plots
[outzones]
the output polygon data source for the zones (if unspecied no zone
output is produced; if specied, dimzones must also be specied)
[dimzones]
the dimensions of the zones in coordinate system units (this value should
be an exact multiple of the plot dimensions), e.g. 1000 or c(1000,2000);
specifying one value results in square zones
[snap]
a value > 0; controls whether the vector grid is aligned with a major
coordinate system interval (supplying a value of 1000 will result in the
grid being aligned to the 1000-mark intervals of the coordinate system);
default=0 (no snap)
[raster]
asuitability (1/0) raster that is used to characterize plots (see help doc-
umentation for further details)
[barrierpoly] a polygon data source representing barriers that cannot be sampled (see
help documentation for further details)
[barrierline] a line data source representing barriers that cannot be crossed (see help
documentation for further details)
[minarea]
the threshold, expressed as a proportion of the plot area, that is used
to determine whether a plot fragment will be retained as a fragment, or
merged (default=0.8, see help documentation for further details)
[tol]
the tolerance that is used in the merging of plot fragments resulting from
barriers (see help documentation for further details)
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