[R-sig-Geo] Shifting a spatial object by (dx,dy)

[Roger Bivand]

On Wed, 7 Feb 2007, David Forrest wrote:

> Hi,
> 
> I've got a mis-projected UTM zone 18 polygon shapefile, the coordinates of 
> which need a transformation of (+287.4395, -77.5542) added to them to be 
> in WGS84/NAD83 UTM 18.  Since this is a non-standard CRS / non-EPSG CRS, 
> I'm not sure about the best way to fix it.
> 
> Is there some function that would add this offset to the component 
> polygon coordinates, bbox, and labpts data?

No, although it could be done by picking things apart and shifting them 
point for point. My first choice would be to hand-craft a +proj=tmerc CRS 
for the shifted data and use spTransform() in rgdal to move it, probably 
by making the modifications in +x_0= and +y_0= in relation to the correct 
ones for the UTM zone. When the differences between the bounding boxes or 
label points of the input and output data are correct, the fake CRS will 
be the right one.

http://www.remotesensing.org/geotiff/proj_list/transverse_mercator.html

has lots of information.

Roger

> 
> Dave
> 

-- 
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