[R-sig-Geo] expand the dist covariate of the prediction-grid meuse.grid (sp package)

[Christoph Hofer]

Edzer,

Many thanks for the fast and qualified reply.


Christoph

Am 04.05.2010 um 19:33 schrieb Edzer Pebesma:

> sp does not do points-to-line distances, but can do point-to-point
> distances. In the second section I resampled the river boundary so we
> get a closer approximation, because more points. Maybe rgeos can be
> expanded do the real point-to-line things (R != GIS?).
> 
> library(sp)
> data(meuse.riv)
> meuse.sr =
> SpatialPolygons(list(Polygons(list(Polygon(meuse.riv)),"meuse.riv")))
> meuse.sp = as(as(meuse.sr, "SpatialLines"), "SpatialPoints")
> 
> # create a grid:
> grd = SpatialPixels(SpatialPoints(makegrid(meuse.sr)))
> plot(meuse.sr)
> grd = spsample(as(meuse.sr, "Spatial"), type='regular', n=10000)
> points(coordinates(grd))
> d = spDists(grd, meuse.sp)
> d0 = apply(d,1,function(x){x[x==min(x)][1]})
> g0 = SpatialPixelsDataFrame(as(grd, "SpatialPixels"), data.frame(d0=d0))
> spplot(g0, col.regions=bpy.colors())
> 
> # for finer discretized
> meuse.sp = as(spsample(as(meuse.sr, "SpatialLines"),type="regular",
> n=1000),    "SpatialPoints")
> d = spDists(grd, meuse.sp)
> g0$d1 = apply(d,1,function(x){x[x==min(x)][1]})
> pplot(g0, col.regions=rev(bpy.colors()))
> 
> Hope this helps,
> --
> Edzer
> 
> On 05/04/2010 09:39 AM, Christoph Hofer wrote:
>> Dear list
>> 
>> 
>> I would like to expand the covariate "dist"  of the meuse.grid dataset, of the sp package,
>> to the south-east direction. The value of the covariate dist is relative between [0,1].
>> Now, it is not clear for me how I shall calculate the distance between
>> a new gird point and the river (is it the perpendicular between the river border and the grid point)?
>> 
>> I appreciate for any tips or hints.
>> 
>> 
>> 
>> Christoph
>> 
>> 
>> 
>> 
>> 
>> ETH Zurich
>> Christoph Hofer
>> Soil and Terrestrial Environmental Physics
>> Institute of Terrestrial Ecosystems
>> CHN E 50.2
>> Universitätstrasse 16
>> 8092 Zurich, Switzerland
>> phone         (+41) - (0)44 - 633 63 65
>> fax               (+41) - (0)44 - 633 11 23
>> e-mail: christoph.hofer at env.ethz.ch
>> 
>> _______________________________________________
>> R-sig-Geo mailing list
>> R-sig-Geo at stat.math.ethz.ch
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> 
> -- 
> Edzer Pebesma
> Institute for Geoinformatics (ifgi), University of Münster
> Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
> 8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
> http://www.52north.org/geostatistics      e.pebesma at wwu.de