<br><div>Hi,</div><div><br></div><div>I notice that Trac revision 1874 updated the "epsg" definitions file to use +towgs84= instead of +datum=</div><div>as expressed briefly in this comment:</div><div><br></div><div>
"<span class="Apple-style-span" style="font-family: Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif; font-size: 11px; border-collapse: collapse; ">epsg update from GDAL - add TMSO and change of named datums to defined form (<a class="assigned ticket" href="http://trac.osgeo.org/proj/ticket/18" title="defect: lack of support for South African projections (assigned)" style="text-decoration: none; color: rgb(187, 0, 0); border-bottom-width: 1px; border-bottom-style: dotted; border-bottom-color: rgb(187, 187, 187); ">#18</a>)"</span></div>
<div><span class="Apple-style-span" style="font-family: Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif; font-size: 11px; border-collapse: collapse; "><br></span></div><div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; ">I was wondering where I could read about the rationale for the latter change. Ticket #18</span></font></div>
<div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; ">seems to be about the addition of TMSO only as far as I can see.</span></font></div>
<div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; "><br></span></font></div><div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; ">This seems to make a difference for the NAD27 coordinate systems as far as I understand</span></font></div>
<div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; ">how PROJ.4 </span></font><span class="Apple-style-span" style="font-family: Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif; border-collapse: collapse; ">works.</span></div>
<div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; "><br></span></font></div><div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; ">As I understand it, the +datum=NAD27 form (for example) uses datum shift files whereas</span></font></div>
<div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; ">the replacement +towgs84=-10,158,187,0,0,0,0 form represents an average shift, right?</span></font></div>
<div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; "><br></span></font></div><div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; ">Can someone either explain why this change was made or point me at a discussion </span></font></div>
<div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; ">perhaps in another list?</span></font></div>
<div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; "><br></span></font></div><div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; ">Thank you very much,</span></font></div>
<div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; "><br></span></font></div><div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; ">carl</span></font></div>
<div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse;"><br></span></font></div><div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse;"><br>
</span></font></div><div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; "><br></span></font></div>
<div><font class="Apple-style-span" face="Verdana, Arial, 'Bitstream Vera Sans', Helvetica, sans-serif"><span class="Apple-style-span" style="border-collapse: collapse; "><br></span></font></div>