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Read shapefile with correct proj4string for the data

2 messages · Jim Burke, Roger Bivand

Original
Jim Burke
# 
Hi I have a shapefile that I open successfully
but incorrectly (data is not in lat long format)
with the following. I am curious what the correct
proj4string would be given the "prj" file below.

my_map_sp <- readShapePoly("my_shape_file.shp",
IDvar="ID", proj4string=CRS("+proj=aea
+ellps=GRS80 +datum=WGS84"))

What is the correct "proj4string" format
given the below?

PROJCS["NAD_1983_StatePlane_Texas_North_Central_FIPS_4202_Feet",
GEOGCS["GCS_North_American_1983",
DATUM["D_North_American_1983",
SPHEROID["GRS_1980",6378137.0,298.257222101]],
PRIMEM["Greenwich",0.0],
UNIT["Degree",0.0174532925199433]],
PROJECTION["Lambert_Conformal_Conic"],
PARAMETER["False_Easting",1968500.0],
PARAMETER["False_Northing",6561666.666666666],
PARAMETER["Central_Meridian",-98.5],
PARAMETER["Standard_Parallel_1",32.13333333333333],
PARAMETER["Standard_Parallel_2",33.96666666666667],
PARAMETER["Latitude_Of_Origin",31.66666666666667],
UNIT["Foot_US",0.3048006096012192]]

Thanks,
Jim Burke
Roger Bivand
#
On Fri, 24 Apr 2009, Jim Burke wrote:

            

      
      
      
    

        
library(rgdal)
EPSG <- make_EPSG()
EPSG[grep("Texas North Central", EPSG$note),]

so most likely CRS("+init=epsg:2276")

(the offsets are given in ftUS in your source, in m in EPSG)

Using readOGR() in rgdal would read the *.prj file too, but readOGR() 
doesn't (yet) handle as many DBF field types as readShapeSpatial() in 
maptools (dates are a problem).

Hope this helps,

Roger