Pardon my ignorance here - I'm not (nor do I wish to become) a GIS expert with detailed knowledge of all the ins and outs of CRSs. While I can understand that to some users it could be critical to know with ultimate accuracy the location of any specified point as a world coordinate, what ultimately matters to me is to be able to agree with other users that we consistently interpret our mapping data in the same way - point A is always in the same place on each of our systems, subject obviously to specifying the CRS.
Using shapefiles, as I understand it, the .prj file specifies how everything should line up. For OSGB 1936 this has historically been PROJCS["OSGB_1936_British_National_Grid",GEOGCS["GCS_OSGB 1936",DATUM["D_OSGB_1936",SPHEROID["Airy_1830",6377563.396,299.3249646]],PRI MEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transver se_Mercator"],PARAMETER["latitude_of_origin",49],PARAMETER["central_meridian ",-2],PARAMETER["scale_factor",0.9996012717],PARAMETER["false_easting",40000 0],PARAMETER["false_northing",-100000],UNIT["Meter",1]] If I get layers from Ordnance Survey, my county council GIS department or other town and parish councils, I would expect my example point A to stay in the same place whatever GIS software I use. I'm not sure what is being suggested here as a fix. Is it going back to the pre 1.8.0 solution or providing an alternative CRS that the user will need to select for all affected layers in every project? If the latter it will potentially cause problems for those of us sharing projects between machines using different version of QGIS. Sorry - I'm just having trouble getting my head around this! Andrew Chapman -----Original Message----- From: Even Rouault [mailto:[email protected]] Sent: 31 January 2013 12:24 To: Andrew Chapman Cc: [email protected] Subject: Re: [Qgis-user] EPSG:27700 - OSGB 1936 / British National Grid shapefiles are incorrectly interpreted by QGIS 1.8.0 and later Selon Andrew Chapman <[email protected]>: There's a GDAL ticket about that : http://trac.osgeo.org/gdal/ticket/4597 Frank, I've attached in it a libgeotiff patch that should solve this by defining an override. _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user
