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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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