[R-sig-Geo] Can you query points with a polygon?

Pierce, Ken ken.pierce at oregonstate.edu
Wed Dec 13 05:56:10 CET 2006 

If I have a set of points from a shapefile (or generated in R) and a
polygon from a shapefile, can I use the polygon to select the points
that fall within it? One of the many packages must do it but I can't
seem to figure which one.

Thanks,

Kenneth B. Pierce Jr.
Research Ecologist
Landscape Ecology, Modeling, Mapping and Analysis Team 
PNW Research Station - USDA-FS 
3200 SW Jefferson Way,  Corvallis,  OR 97331 
ken.pierce at oregonstate.edu
541 750-7393 
http://www.fsl.orst.edu/lemma/gnnfire



 

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Today's Topics:

   1. Re: project the lat./long. to x/y (zhijie zhang)


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Message: 1
Date: Mon, 11 Dec 2006 09:05:44 +0800
From: "zhijie zhang" <epistat at gmail.com>
Subject: Re: [R-sig-Geo] project the lat./long. to x/y
To: Roger.Bivand at nhh.no
Cc: r-sig-geo at stat.math.ethz.ch
Message-ID:
	<2fc17e30612101705k1c06bef5of751d5764dd1d360 at mail.gmail.com>
Content-Type: text/plain

*Dear Roger Bivand* ,
  Your suggestions are very good, which gives me a general method to do
projections.
  Thanks.


On 12/6/06, Roger Bivand <Roger.Bivand at nhh.no> wrote:
>
> On Wed, 6 Dec 2006, zhijie zhang wrote:
>
> > Dear friends,
> >   I had a point pattern dataset, whose locations was defined
> by  lat./long..
> > In the past, I used ARCGIS to specify its coordinate system and the 
> > projection method, now i want to do it in R. I don't know how to do 
> > it, because it needs me to specify the *Geographic Coordinate System

> > and the Projected Coordinate System.* Maybe i mistake the 
> > information in ARCGIS
> and
> > only the projection method need to be specified because of my poor
> knwledge
> > on coordiante systems.
>
> Coordinate systems are unusually difficult to understand for
everybody!
>
> In rgdal:
>
> EPSG <- make_EPSG()
> EPSG[grep("Xian", EPSG$note), 1:2]
>
> gives a list of the known projections including "Xian",
>
> among which:
>
> CRS("+init=epsg:2384")
>
> looks promising. The a= and b= specify the ellipsoid used, but I have 
> not been able to find an authority to confirm that it is D_Xian_1980. 
> One way to check would be to take a long/lat value in WGS84 (for known

> datum) and convert it to the target projection in both ArcGIS and with

> spTransform() in rgdal, and see how far they differ. I do not see 
> anything helpful in http://www.asprs.org/resources/GRIDS - referenced 
> on the make_EPSG help page, which is often a good authority, so you 
> may need to double-check with local sources.
>
> The way to go would be to make your (point?) data set into a Spatial* 
> object with a projection argument like CRS("+proj=longlat 
> +ellps=WGS84") if the ellipsoid is correct, and use spTransform to get

> to the Gauss_Kruger Xian datum representation.
>
> Roger
>
> PS. Yes, the Windows binary of the rgdal version you give below was 
> built on R 2.4.0 (you are on Windows?). You need to download a Windows

> binary package manually from 
> http://cran.r-project.org/bin/windows/contrib/
> (there is a 0.4-12 version for R 2.3); the same may apply to other 
> packages.
>
> >
> > ---------------------------------------------------The information 
> > in
> ARCGIS
> > after projecting the dataset-------
> > Geometry Type: Point
> >
> > *Geographic Coordinate System:* #specify the coordinate system 
> > GCS_Xian_1980
> > Datum: D_Xian_1980
> > Prime Meridian: 0
> >
> > *Projected Coordinate System:* Xian_1980_3_Degree_GK_CM_117E
#specify
> the
> > projection method
> > Projection: Gauss_Kruger
> > False_Easting: 500000.00000000
> > False_Northing: 0.00000000
> > Central_Meridian: 117.00000000
> > Scale_Factor: 1.00000000
> > Latitude_Of_Origin: 0.00000000
> > Linear Unit: Meter (1.000000)
> >
> ----------------------------------------------------------------------
> ------------------------------------------------------
> > mapproject(x, y, projection="", parameters=NULL,
> orientation=NULL)  *#only
> > allows us to define the projected coordinate system Anybody knows 
> > how to finish it in R? Maybe rgdal() can it, but it's a
> liitle
> > difficult for me*.
> >
> > *Example of my dataset:*
> >
> > ID  CLASS SOILTEM AIRTEM GHEIGHT H      *LAT     LONG*
> > 1   1      19       20      50        30.61688 117.4140
> > 2   1      19       21      65        30.61686 117.4140
> > 3   2      20       22      55        30.61680 117.4139
> > 4   3      20       26      10        30.61675 117.4139
> > 5   4      20       23      75        30.61679 117.4140
> > 6   1      21       21      55        30.61685 117.4141
> >
> > BTW, when i load the package rgdal, the following errors 
> > appear,*where
> is
> > the wrong*? Does it mean i need to use the R2.4.0 version?
> > error in load(dataFile, ns) : ReadItem uncorrect：no class 25 
> > Warning message:
> > package'rgdal'is build with R2.4.0
> > error: package'rgdal' R's input code fail
> > error: 'rgdal'package/name space load fail， 
> > -------------------------------package information
> > ----------------------------
> > R : Version 2.3.1 (2006-06-01)
> > rgdal_0.5-1
> > ---------------------------------------------
> >
> >
>
> --
> 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.Bivand at nhh.no
>
>


--
With Kind Regards,

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Zhi Jie,Zhang ,PHD
Tel:86-21-54237149   epistat at gmail.com
Dept. of Epidemiology,school of public health,Fudan University
Address:No. 138 Yi Xue Yuan Road,Shanghai,China
Postcode:200032
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