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<TITLE>RE: [Gdal-dev] Defining Australian Map Grid in GDAL</TITLE>
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<P><FONT SIZE=2 FACE="Arial">Andrew,</FONT>
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<P><FONT SIZE=2 FACE="Arial">You have to be careful with AGD-based projections in Proj4, because the definitions that exist in Proj4 are not correct (problem with datums). I'm attaching a file with correct definitions for AGD-based projections. I have myself spent several days trying to figure out why my coordinates were up to 200m off, only to realise that Proj4 does not appear to use the AGD84 and AGD66 datum correctly.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">Just for the record:</FONT>
<BR><FONT SIZE=2 FACE="Arial">AMG66 = UTM + AGD66-datum</FONT>
<BR><FONT SIZE=2 FACE="Arial">AMG84 = UTM + AGD84-datum</FONT>
<BR><FONT SIZE=2 FACE="Arial">MGA94 = UTM + GDA94-datum (where GDA94 can be substituted with WGS84)</FONT>
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<P><FONT SIZE=2 FACE="Arial">Be careful with the acronyms. You wouldn’t be the first to start construction in the wrong spot :)</FONT>
<BR><FONT SIZE=2 FACE="Arial">For your image, I guess just override the projection, and project from Latlong AGD84 (epsg:4203, bottom of file I sent) to Latlong WGS84.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">Regards,</FONT>
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<P><FONT SIZE=2 FACE="Arial">Jacob</FONT>
<BR><FONT SIZE=2 FACE="Courier New"> </FONT>
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<P><B><FONT COLOR="#009500" FACE="Arial">J</FONT><FONT COLOR="#009500" SIZE=1 FACE="Arial">ACOB</FONT> <FONT COLOR="#009500" FACE="Arial">D</FONT><FONT COLOR="#009500" SIZE=1 FACE="Arial">ELFOS<BR>
</FONT><FONT COLOR="#009500" FACE="Arial">GIS</FONT><FONT COLOR="#009500" SIZE=1 FACE="Arial"></FONT> <FONT COLOR="#009500" FACE="Arial">A</FONT><FONT COLOR="#009500" SIZE=1 FACE="Arial">NALYST</FONT><BR>
</B><FONT COLOR="#000000" SIZE=2 FACE="Arial">Maunsell Australia Pty Ltd<BR>
629 Newcastle Street, Leederville, WA 6007</FONT>
<BR><FONT COLOR="#000000" SIZE=2 FACE="Arial">PO Box 81, Leederville, WA 6902</FONT>
<BR><FONT COLOR="#000000" SIZE=2 FACE="Arial">Western Australia</FONT>
<BR><FONT COLOR="#000000" SIZE=2 FACE="Arial">ABN 20 093 846 925<BR>
<BR>
Tel + 61 8 9281 6185<BR>
Fax + 61 8 9281 6297<BR>
</FONT><U><FONT COLOR="#009C21" SIZE=2 FACE="Arial">jacob.delfos@maunsell.com</FONT></U>
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<P><FONT FACE="Arial" SIZE=2 COLOR="#000000"> <<agd84_agd66_proj4.txt>> </FONT>
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<P><FONT SIZE=2 FACE="Courier New">» -----Original Message-----</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» From: gdal-dev-bounces@lists.maptools.org </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» [</FONT><A HREF="mailto:gdal-dev-bounces@lists.maptools.org"><U><FONT COLOR="#0000FF" SIZE=2 FACE="Courier New">mailto:gdal-dev-bounces@lists.maptools.org</FONT></U></A><FONT SIZE=2 FACE="Courier New">] On Behalf Of </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» Andrew Williams</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» Sent: 28 February 2006 22:27</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» To: gdal-dev@lists.maptools.org</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» Subject: [Gdal-dev] Defining Australian Map Grid in GDAL</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» Hello folks.</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» I'm having trouble with a Geotiff. </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» The scan is a topographic map sheet. The cartography and grid </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» on the sheet is based on AMG (Australian Map Grid). It is a </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» UTM projection based on the Australian National Spheroid, </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» ellps=aust_SA I believe.</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» My problem is that the GeoTiff has been georefernced as UTM </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» ellps=GRS80 datum=WGS84 incorrectly.</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» My intent is to gdalwarp the image to latlong WGS84.</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» I have tried for the better part of a day to attempt to </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» override or otherwise correct the georeferncing. Without success.</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» I have been very successful with GDAL in the past, but this </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» has stopped me.</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» The problem is that I can't seem to fully define AMG "enough" </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» to allow GDALwarp to reproject the image. It seems to default </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» to the source as being UTM WGS84.</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» I attempted to gdal_translate the image using the corrected </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» definition and then gdalwarp image, but that also failed.</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» the definition I have been using is "+proj=tmerc </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» +ellps=aust_SA +lat_0=0 +lon_0=147 +x_0=500000 +y_0=10000000 </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» +k=0.9996 +south"</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» regards</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» Andrew</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» </FONT>
<BR><FONT SIZE=2 FACE="Courier New">» _______________________________________________</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» Gdal-dev mailing list</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» Gdal-dev@lists.maptools.org</FONT>
<BR><FONT SIZE=2 FACE="Courier New">» </FONT><A HREF="http://lists.maptools.org/mailman/listinfo/gdal-dev"><U><FONT COLOR="#0000FF" SIZE=2 FACE="Courier New">http://lists.maptools.org/mailman/listinfo/gdal-dev</FONT></U></A>
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