5 messages · Aleksandr Andreev, Baptiste Auguie, Rainer M Krug +2 more
In R's maptools package, is there a built-in function to test if a given point is "inside" a given polygon on the map? The map was loaded from an ESRI Shapefile. The point's latitude and longitude are known. Thank you! Aleks
------------------------ Aleksandr Andreev Fulbright Fellow Graduate School of Management St Petersburg State University
I don't know about the maptools package but one general way to do this would be to compute the convex hull (?chull) of the augmented set of points and test if the point belongs to it. Hope this helps, baptiste
In R's maptools package, is there a built-in function to test if a given point is "inside" a given polygon on the map? The map was loaded from an ESRI Shapefile. The point's latitude and longitude are known. Thank you! Aleks -- ------------------------ Aleksandr Andreev Fulbright Fellow Graduate School of Management St Petersburg State University
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
_____________________________ Baptiste Augui? School of Physics University of Exeter Stocker Road, Exeter, Devon, EX4 4QL, UK Phone: +44 1392 264187 http://newton.ex.ac.uk/research/emag
On Thu, Feb 5, 2009 at 3:21 PM, Aleksandr Andreev
In R's maptools package, is there a built-in function to test if a given point is "inside" a given polygon on the map? The map was loaded from an ESRI Shapefile. The point's latitude and longitude are known.
If everything else fails, convert the shape file into a raster and "drill down" at the location of the points. Rainer
Thank you! Aleks -- ------------------------ Aleksandr Andreev Fulbright Fellow Graduate School of Management St Petersburg State University
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology, UCT), Dipl. Phys. (Germany) Centre of Excellence for Invasion Biology Faculty of Science Natural Sciences Building Private Bag X1 University of Stellenbosch Matieland 7602 South Africa
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Renaud Lancelot <renaud.lancelot <at> gmail.com> writes:
See function pip (point in polygon) in package splancs. Renaud 2009/2/5 Rainer M Krug <r.m.krug <at> gmail.com>
On Thu, Feb 5, 2009 at 3:21 PM, Aleksandr Andreev <aleksandr.andreev <at> gmail.com> wrote:
In R's maptools package, is there a built-in function to test if a given point is "inside" a given polygon on the map? The map was loaded from an ESRI Shapefile. The point's latitude and longitude are known.
The initial question was not put clearly. The pip function in splancs will work for a two-column matrix of points, but not for the object in question, if it was read in from a shapefile using readShapeSpatial(). In that case, the object is a SpatialPolygonsDataFrame as defined in the sp package, and the overlay() methods in sp should be the place to look - see ?"overlay-methods". Typically, one would define the query point(s) as a SpatialPoints object, and overlay it on the input object. The output is a vector of indices, showing which Polygons object the points lie in, or NA if they do not. Roger Bivand PS. These kinds of questions typically get more focussed response on the R-sig-geo list; further, RSiteSearch() with 'point polygon' does show many useful avenues.
If everything else fails, convert the shape file into a raster and "drill down" at the location of the points. Rainer