[R-sig-Geo] stuck on importing and projecting shapefiles

[Noli Sicad]

Hi Julie,


Probably you can downloading and installing using rgdal for Mac OS X
from this site

http://www.kyngchaos.com/software:frameworks

~~~~~~~~~
GDAL

    *
      GDAL framework v1.6.3-1 [44.9 MiB] {requires UnixImageIO, GEOS,
SQLite3 and PROJ frameworks}
    *
      ECW plugin v1.6.2-1 [2.9 MiB] (for any GDAL 1.6.x version)
    *
      MrSID plugin v1.6.1-1 [2.9 MiB] (for any GDAL 1.6.x version)
    *
      GRASS plugin is now a separate install, available with the GRASS
installer.
    *
      rgdal 0.6.22-1 - R 2.10 package [1.5 MiB] (for any GDAL 1.6.x version)
    *
      rgdal 0.6.18-1 - R 2.9 package [1.4 MiB] (for any GDAL 1.6.x version)

~~~~~~~~~~~~~~~~~

Noli


On 12/31/09, alexandre villers <alexandre.villers at cebc.cnrs.fr> wrote:
> Hey Julie,
>
> The main problem, for what I understood of working with R and spatial
> objects, is that you are using the wrong tools to import your data. Maptools
> is mostly deprecated for all the import export function with
> shapefile/rasters (but still holds interesting ones for other jobs).
> You'll have to struggle a bit and get rgdal to work on your Mac !
> http://cran.r-project.org/bin/macosx/
> Once this is done, it will be much easier to do the job. GDAL is a very
> powerful, essential tool to import export data to/from R. So get to the help
> list for MAC, the forum and check if
> - rgdal is compatible for your version of R MAC
> - look for all the packages necessary to compile this packages (I couldn't
> download and compile rgdal with linux ubuntu because a small package was
> missing...). Just check through the documentation which packages are
> necessary to compile rgdal with MAC.
>
> Once this is done, your work will be much more simple
>
> You will find all the help you need on the rgdal/sp helpfile and on the
> Internet. But do not hesitate to ask questions on the list.
>
>
> Best regards and good luck.
>
> Alex
>
> PS: I'm pretty sure a R / rgdal /MAC user will help you with this !
>
> -----Original Message-----
> From: Julie Lee-Yaw <julleeyaw at yahoo.ca>
> To: r-sig-geo at stat.math.ethz.ch
> Date: Wed, 30 Dec 2009 15:32:46 -0800 (PST)
> Subject: [R-sig-Geo] stuck on importing and projecting shapefiles
>
> Hi,
> I am new to both R and spatial data and am very stuck on what I think should
> be a simple analysis. I am trying to do a polygon overlay analysis of two
> shapefiles from different sources. Before proceeding to my overlay
> functions, I am trying to plot my shapefiles to double check that they line
> up properly. In R, I am using PBSmapping and maptools and the following
> script:
>
> ## read in first shapefile using maptools so I can pull out only those
> polygons that are labeled "blue"
>
> s1=readShapePoly("shapefile1")
> s1blue=s1[s1$SYMB=="BLUE",]
> s1PS=SpatialPolygons2PolySet(sp1blue)
> shape1=combinePolys(sp1PS)
> attr(shape1,"projection")<-"LL"
>
> ## read in second shapefile using PBSmapping routine (in this case, I need
> to use importShapefile because I have previously modified this function to
> import only select polygons from this file
>
> shape2<-importShapefile("shapefile2", projection="LL")
>
> ## trying to plot both together:
>
> plotPolys(shape1) ##produces reasonable looking plot
> addPolys(shape2)
>
> ## I get the following error message
>
> In .checkProjection(projectionPlot, projectionPoly) :
>   The data's 'projection' attribute (LL) differs from the
> projection of the plot region (NA).
>
> This leads me to think that the projections are different and thus my
> downstream calculations of intersection areas will be off. The first
> shapefile is projected and has the following prj file attached:
>
> PROJCS["Clarke_1866_Lambert_Conformal_Conic",GEOGCS["GCS_Clarke_1866",DATUM["D_Clarke_1866",SPHEROID["Clarke_1866",6378206.4,294.9786982]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Lambert_Conformal_Conic"],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-95.0],PARAMETER["Standard_Parallel_1",49.0],PARAMETER["Standard_Parallel_2",77.0],PARAMETER["Latitude_Of_Origin",49.0],UNIT["Meter",1.0]]
>
> The second shapefile is unprojected and the metadata indicates:
> projection parameters: units: decimal degrees
> Datum: North America 1983
>
> Since I'm using a MAC and can't figure out how to load rgdal, I have tried
> importing both shapefiles into QGIS (a separate GIS program), reprojecting
> them and exporting them from there and re-applying my R code but I get the
> same error message. Does anyone have any suggestions as to what I might be
> doing wrong and how I can get these shapefiles into a common projection so
> that I can calculate the area of their intersection? Thanks in advance for
> the help!
>
>
>
> Alexandre Villers
> PhD. Candidate
> Team Agripop
> CEBC CNRS UPR 1934
> 79360 Beauvoir sur Niort
>
> Phone: +33 (0)549 099 613
>
>
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