<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hey there<div><br></div><div>I came across this problem before and had to make some adjustments to my epsg file. Try replacing the current <27700> line in your epsg file with this one:</div><div><br></div><div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 10px/normal 'Courier New'; "># OSGB 1936 / British National Grid</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 10px/normal 'Courier New'; "><27700> +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.999601 +x_0=400000 +y_0=-100000 +ellps=airy +towgs84=446.448,-125.157,542.060,0.1502,0.2470,0.8421,-20.4894 +units=m +no_defs no_defs <> </div><div><font class="Apple-style-span" face="'Courier New'" size="2"><span class="Apple-style-span" style="font-size: 10px;"><br></span></font></div><div><font class="Apple-style-span" face="'Courier New'" size="2"><span class="Apple-style-span" style="font-size: 10px;">Hopefully that will sort your problem</span></font></div><div><font class="Apple-style-span" face="'Courier New'" size="2"><span class="Apple-style-span" style="font-size: 10px;"><br></span></font></div><div><font class="Apple-style-span" face="'Courier New'" size="2"><span class="Apple-style-span" style="font-size: 10px;">Best</span></font></div><div><font class="Apple-style-span" face="'Courier New'" size="2"><span class="Apple-style-span" style="font-size: 10px;"><br></span></font></div><div><font class="Apple-style-span" face="'Courier New'" size="2"><span class="Apple-style-span" style="font-size: 10px;">Stuart</span></font></div><div><font class="Apple-style-span" face="'Courier New'" size="2"><span class="Apple-style-span" style="font-size: 10px;"><br></span></font></div><div><font class="Apple-style-span" face="'Courier New'" size="2"><span class="Apple-style-span" style="font-size: 10px;">Stuart Eve</span></font></div><div><font class="Apple-style-span" face="'Courier New'" size="2"><span class="Apple-style-span" style="font-size: 10px;">L - P : Archaeology</span></font></div><div><font class="Apple-style-span" face="'Courier New'" size="2"><span class="Apple-style-span" style="font-size: 10px;"><a href="mailto:stuarteve@gmail.com">stuarteve@gmail.com</a></span></font></div><div><div>On 13 Jul 2009, at 15:33, John A Stevenson wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Hi,<br><br>I have been using GRASS GIS, which uses Proj4 to convert between projections. I have data in OSGB36 projection (a Nextmap DEM and a scanned in OS map), and I am trying to merge it with GPS data (from WGS84). When I do the conversion (using EPSG:27700) I find that the GPS data plot about 100 m east of where they should do.<br><br>Has anyone else had this trouble converting between OSGB36 and WGS84 coordinate systems? What is the solution? Are there any other conversion parameters available?<br><br>Cheers<br><br>John<br><br>-- <br><br><br>Dr John Stevenson<br>Postdoctoral Research Associate<br>School of Earth, Atmospheric and Environmental Sciences<br>Williamson Building (Room 2.42)<br>University of Manchester<br>Manchester M13 9PL, UK<br>tel. +44(0)161 306 6585; fax. +44(0)161 306 9361;<br><a href="mailto:john.stevenson@manchester.ac.uk">john.stevenson@manchester.ac.uk</a> <br>_______________________________________________<br>UK mailing list<br><a href="mailto:UK@lists.osgeo.org">UK@lists.osgeo.org</a><br>http://lists.osgeo.org/mailman/listinfo/uk<br></div></blockquote></div><br></div></body></html>