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: [EMAIL PROTECTED] _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo