Russell: I do not know about the coordinate systems in use in UK, so I do not know the reason why you reverted the place names projected coordinates to geographic coordinates and what was their original coordinate system. Anyhow, I see a problem on using just three decimal positions on the decimal degrees values for lat and long. Just think that each arcsecond corresponds to roughly 30 meters on the ground! You should use some transformation that can give seven or even eight decimal positions for the lat and long values. Or try to use the projected coordinates from the second data set, if the coordinate system is known to EPSG.
Regards, Joao -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Russell Horn Sent: Wednesday, November 21, 2007 5:21 PM To: [email protected] Subject: [postgis-users] Problem with mismatched coordinate systems Hi, I am very new to PostGIS, please bear with me. I've had a lot of help from #postgis on IRC but I continue to have trouble and hope someone here can assist. I have two data sets from the UK Ordnance Survey which when imported to PostGIS and plotted are not matching up: http://exiled.albanach.com/chester.png One data set contains shape files (no .prj file) which give me an outline of part of the UK. The data set is available here: http://www.ordnancesurvey.co.uk/products/boundaryline/sampledata/Layered _Shape.zip The documentation states that the coordinate system is National Grid (NG). I understand this is OSGB1936 / EPSG:27700 The other data set contains a list of place names, together with Eastings and Northings like this: CHESTER*CHESHIRE COUNTY*340363*366880 I have then converted that to Long Lat to give me 53.196,-2.894,CHESTER I can paste my Long Lat values into Google maps and get the right place, so that conversion seems to have worked. To import my shape files I did this: shp2pgsql -s 27700 county_region.shp public.ch_county > /tmp/county.sql To import my place names, I did this: ogr2ogr -f "ESRI Shapefile" gaz/ chester.csv Where chester.csv looks like this lat,long,value 53.196,-2.894,CHESTER I then did ogr2ogr -f "ESRI Shapefile" gaz/ chester.csv ogr2ogr -f "ESRI Shapefile" gaz/ os.vrt To make my shapefiles where os.vrt looks like this: <OGRVRTDataSource> <OGRVRTLayer name="OS_Gazetteer"> <SrcDataSource relativeToVRT="1">gaz</SrcDataSource> <SrcLayer>chester</SrcLayer> <GeometryType>wkbPoint</GeometryType> <LayerSRS>EPSG:27700</LayerSRS> <GeometryField encoding="PointFromColumns" x="long" y="lat"/> </OGRVRTLayer> </OGRVRTDataSource> Changing LayerSRS value didn't seem to change anything. I converted to sql like this: shp2pgsql OS_Gazetteer.shp public.chesgaz > gaz.sql I then imported my two SQL files into Postgres. When plot my data using qgis I end up with Chester being plotted way off my map like the image I pointed to earlier: http://exiled.albanach.com/chester.png I know I'm doing something wrong here, but I'm at a bit of a loss as to what it is, and where to go from here. Any help would be very much appreciated. Thanks, Russell _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
