On 03/29/2013 02:20 PM, Ross Ahmed wrote:
> Many thanks Roger.
>
> I thought proj4string(spAll) <- CRS("+proj=longlat +ellps=WGS84
> +datum=WGS84") took care of projection, but obviously not.
No, it only sets the proj4string, which is NA if not set; +proj=longlat
indicates unprojected data, i.e. coordinates reflect longitude and latitude.
> How do I project?
with spTransform in package rgdal - you need to choose a target CRS for
this.
>
> Ross
>
> On 29 Mar 2013, at 12:54, Roger Bivand <roger.biv...@nhh.no> wrote:
>
>> On Fri, 29 Mar 2013, Ross Ahmed wrote:
>>
>>> Hi all,
>>>
>>> I have this list of polygons:
>>>
>>> library(sp)
>>> p1 <- Polygon(cbind(c(-1.672487,-1.663689,-1.663185,-1.672258,-1.672487),
>>> c(55.58951,55.58948,55.58249,55.58260,55.58951)))
>>> p2 <- Polygon(cbind(c(-1.663689, -1.655508, -1.65514, -1.6633, -1.663689),
>>> c(55.589485, 55.589554, 55.582396, 55.582428,
>>> 55.589485)))
>>> p3 <- Polygon(cbind(c(-1.672224, -1.663046, -1.662525, -1.672137,
>>> -1.672224),
>>> c(55.582142, 55.582044, 55.575139, 55.575348,
>>> 55.582142)))
>>>
>>> sp1 <- Polygons(list(Polygon(p1)),"p1")
>>> sp2 <- Polygons(list(Polygon(p2)),"p2")
>>> sp3 <- Polygons(list(Polygon(p3)),"p3")
>>> spAll <- SpatialPolygons(list(sp1, sp2, sp3))
>>> proj4string(spAll) <- CRS("+proj=longlat +ellps=WGS84 +datum=WGS84")
>>>
>>>
>>> ?.and also this single polygon:
>>>
>>> poly1 <- Polygon(cbind(c(-1.666566, -1.659071, -1.658532, -1.666459,
>>> -1.666566),
>>> c(55.586296, 55.586357, 55.580414, 55.580505,
>>> 55.586296)))
>>> spoly1 <- Polygons(list(Polygon(poly1)),"poly1")
>>> spoly1 <- SpatialPolygons(list(spoly1))
>>> proj4string(spoly1) <- CRS("+proj=longlat +ellps=WGS84 +datum=WGS84")
>>>
>>>
>>> I need to find the proportion of ?spoly1? that is overlapped by ?sp1?,
>>> ?sp2?, ?sp3? and no polygon. The output should be something like:
>>>
>>> 0.40, 0.30, 0.20, 0.10
>>
>> library(rgeos)
>> gArea(spoly1)
>> gArea(gIntersection(spAll, spoly1, byid=TRUE), byid=TRUE)/gArea(spoly1)
>>
>> but note the warnings. You'll need to project both objects to get a proper
>> measure.
>>
>> Roger
>>
>>>
>>> Thanks
>>> Ross
>>>
>>>
>>>
>>> [[alternative HTML version deleted]]
>>
>> --
>> Roger Bivand
>> Department of Economics, NHH Norwegian School of Economics,
>> 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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--
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.pebe...@wwu.de
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