At 08:49 20/01/2009, Roger Bivand wrote:
On Mon, 19 Jan 2009, Struve, Juliane wrote:
Dear list members,
I would like to look for attributes (e.g.
distance from the shore) of spatial points in
other data sets (e.g. dist_shoreDF) after
matching the points in fishlocationDF and dist_shoreDF by their coordinates.
The most direct way for planar coordinates is to
use functions in the spatstat package, to give
the distance between a point and a line. You'll
need to ceorce from sp objects to spatstat
objects using methods in the maptools package, something like:
library(maptools)
library(spatstat)
fish_ppp <- as(as(fishlocationDF, "SpatialPoints"), "ppp")
shore_psp <- as(as(shoreDF, "SpatialLines"), "psp")
As far as I can see, the pairdist method exists
for either ppp or psp objects, but not for a combination, but I may be wrong.
Maybe
dist_fish_shore <- project2segment(fish_ppp, shore_psp)
Best,
Marcelino
There is an internal function called distppll()
which takes a matrix of points and a single line
segment as a matrix, which can be used, but
which involves some coding to extract the matrices from the input objects.
http://www.csiro.au/resources/Spatial-Point-Patterns-in-R.html
is a very useful resource, but there isn't too much on line segements yet.
Hope this helps,
Roger
PS. Is there a function in PBSmapping to do
this, perhaps handling geographical coordinates?
fishlocationDF$dist=dist_shoreDF$dist[match(dist_shoreDF$coordinates,
fishlocationDF$coordinates)] does not work but
illustrates what I am trying to do.
How can I deal with the two coordinates that
every point has ? Would it be possible to
coerce both x and y-coordinate into one column
in order in order to apply the match() function
? Or is there a better way of approaching this
? I would be grateful for a hint.
Thank you for your time.
Juliane
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--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: roger.biv...@nhh.no
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________________________________
Marcelino de la Cruz Rot
Departamento de Biología Vegetal
E.U.T.I. Agrícola
Universidad Politécnica de Madrid
28040-Madrid
Tel.: 91 336 54 35
Fax: 91 336 56 56
marcelino.delac...@upm.es
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