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. 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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