<HTML><HEAD><TITLE>[Gvsig_english] gvSIG and OSGB36 (EPSG:27700)</TITLE>
<META http-equiv=Content-Type content="text/html; charset=unicode">
<META content="MSHTML 6.00.6000.17098" name=GENERATOR></HEAD>
<BODY>
<DIV id=idOWAReplyText95884>
<DIV><FONT face="Times New Roman" color=#000000 size=3>Hello, Nick,</FONT></DIV>
<DIV> </DIV>
<DIV>When you do a conversion between EPSG:4326 <--> EPSG:27700 you have to choose the "EPSG transformation" option in the combo box and gvSIG will automatically list 5 or 6 possible options: one for England, one for England+Wales, etc. I have used that particular conversion several times without a problem. That gives you an accuracy of about 2 metres (somethimes 1 metre, sometimes 3 metres, etc)</DIV>
<DIV> </DIV>
<DIV>You can also use NTv2 grids for the UK available here (we can assume that ETRS89 and WGS84 are equivalent, if I'm not wrong):</DIV>
<DIV> </DIV>
<DIV><A href="http://lists.maptools.org/pipermail/proj/2006-November/002658.html">http://lists.maptools.org/pipermail/proj/2006-November/002658.html</A></DIV>
<DIV> </DIV>
<DIV>With those grids I think the accuracy will be a few inches, perhaps 1 inch, perhaps 3 inches, etc.</DIV>
<DIV> </DIV>
<DIV>Regards,</DIV>
<DIV><FONT face="Courier New" size=2><FONT face="Times New Roman" size=3>Juan Lucas Domínguez Rubio<BR></FONT>---</FONT></DIV></DIV>
<DIV id=idSignature20679>
<DIV><FONT face="Courier New" size=2><FONT face="Courier New" size=2><FONT face="Courier New" size=2>Prodevelop SL, Valencia (España)</FONT></DIV>
<DIV>
<DIV><FONT face="Courier New" size=2>Tlf.: 96.351.06.12 -- Fax: 96.351.09.68<BR></FONT><A href="http://www.prodevelop.es/"><FONT face="Courier New" size=2>http://www.prodevelop.es</FONT></A><BR><FONT face="Courier New" size=2>---</FONT></DIV></FONT></DIV></FONT></DIV>
<DIV><BR>
<HR>
<FONT face=Tahoma size=2><B>De:</B> gvsig_internacional-bounces@listserv.gva.es en nombre de Nick Hopton<BR><B>Enviado el:</B> jue 28/07/2011 13:03<BR><B>Para:</B> gvsig_internacional@listserv.gva.es<BR><B>Asunto:</B> [Gvsig_english] gvSIG and OSGB36 (EPSG:27700)<BR></FONT><BR></DIV>
<DIV>
<P><FONT size=2>I have recently installed gvSIG Version 1.11.0 (Build 1305) running<BR>under Ubuntu 11.04 (amd64). On checking the Proj4<BR>parameter string that gvSIG uses for EPSG:27700 I found that it was<BR>thus:<BR><BR>PROJ4 string: +proj=tmerc +lat_0=49.0 +lon_0=-2.0 +k=0.9996012717<BR>+x_0=400000.0 +y_0=-100000.0 +ellps=airy +units=m<BR><BR>This string does not include the '+datum=OSGB36' parameter and as a<BR>result the datum shift between OBSG36 and WGS84 will not be applied.<BR>If I recall correctly, the shift between the two datums is something<BR>like 112 metres at Greenwich.<BR><BR>This was a known problem with older versions of Proj4.<BR><BR>Is there any way to edit the parameter string that gvSIG?<BR><BR>Regards,<BR>Nick.<BR><BR><BR><BR>--<BR>View this message in context: <A href="http://osgeo-org.1803224.n2.nabble.com/gvSIG-and-OSGB36-EPSG-27700-tp6629441p6629441.html">http://osgeo-org.1803224.n2.nabble.com/gvSIG-and-OSGB36-EPSG-27700-tp6629441p6629441.html</A><BR>Sent from the gvSIG users mailing list archive at Nabble.com.<BR>_______________________________________________<BR>Gvsig_internacional mailing list<BR>Gvsig_internacional@listserv.gva.es<BR><A href="http://listserv.gva.es/cgi-bin/mailman/listinfo/gvsig_internacional">http://listserv.gva.es/cgi-bin/mailman/listinfo/gvsig_internacional</A><BR></FONT></P></DIV></BODY></HTML>