This algorithm produces higher-quality isopleth lines at the expense of processing time,
and is the same algorithm that is used in the contour command. It interprets the raster as
atriangular regular network and performs a plane intersection to determine the paths of the
contour lines. It does not perform any sort of smoothing on the line.
While lines are always output from this command, you can also optionally specify that
polygons should be created. This does not, however, guarantee that a polygon will be created
for every isopleth. For a polygon to be created, the line must form a complete loop. For the
larger quantiles the isopleths may not form complete loops if the raster has been generated
over too small an extent. It would be inappropriate for a tool to close those isopleths based
on the boundary of the raster extent, as these boundaries do not represent the true position
of those isopleths. Rather than close isopleth lines inappropriately, the tool only converts the
complete loops to polygons and reports a warning message that some lines were not closed.
If you receive that message it is recommended that you regenerate the raster surface over a
larger extent. I have added an ’edgein
ation’ parameter to the kde command to assist with
Two types of polygon outputs are available: full polygons or donut polygons. For full
polygons the smaller isopleth polygons will overlap (and be contained by) the polygons for
larger isopleth values. In the case of donut polygons, only the portion of the polygon repre-
sentingthe interval between twoisopleths is retained, and there are no overalapping polygons.
Always specify dierent output polygon datasets for the poly and donut parameters (never
write both to the same dataset).
Although a ’band’ option is included so that users can identify which band to process in
the case ofmultiband images, it is likely that this tool will most often be run with continuous,
single-band raster data.
isopleth(in, out, quantiles, [band], [poly], [donut]);
the input integer raster data source
the output line data source
quantiles the quantiles (expressed as a proportion or percentage) at which to gen-
erate isopleths, e.g. 0.95 or c(0.5, 0.9, 0.95)
the input band (default=1)
an output polygon data source (the isopleths are converted to polygons;
refer to full documentation for details)
an output polygon data source to which the donut polygons are written
(the isopleths are converted to polygons; refer to full documentation for
isopleth(in="C:ndatankde", out="C:ndatanisopleths.shp", quantiles=c(0.5, 0.9, 0.95));
isopleth(in="C:ndatankde", out="C:ndatanisopleths.shp", quantiles=r.eval(seq(0,100,10)));