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Ken / Brett, The only thing we know for certain is that we are all out of our depths! Regardless, I think we are on the way to solving this. Please find a new srs.db here http://dl.dropbox.com/u/9546967/srs.db. The new file incorporates both towgs84 parameters and a reference to the distortion files. The distortion file values appear to take precedence, but I have included the towgs84 parameters as it looks like the AGD84 distortion files do not cover the states and territories that did not adopt AGD84. Note that I have changed the AGD66 towgs84 parameters to national ones (previously ACT) according to this document (page 31) http://www.icsm.gov.au/gda/gdatm/gdav2.3.pdf. To use the distortion files you need to place these files http://dl.dropbox.com/u/9546967/agd66.gsb http://dl.dropbox.com/u/9546967/agd84.gsb in your Proj data directory (/usr/share/proj on Linux). It is the directory containing the 'epsg' and 'proj_def.dat' files. Make sure that this is the directory your Proj installation is actually using by checking the contents of the PROJ_LIB environment variable (echo $PROJ_LIB). It may not be set, which is OK. It took me about 4 hours to figure out I had set it to an old development directory several years ago! Note that I did try it without the +wktext parameter. It works in Proj (using cs2cs), but QGIS needs it. Let me know how it goes on your test points. Cheers, Roland --
ROLAND HILL Director Four Winds Technology Pty Ltd Ph/Fax : +61 (0)2 6366 9425 Mobile : +61 (0)41 880 7472 roland.h...@fourwindstechnology.com.au Privacy and
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On 24/09/10 07:27, Ken Norris wrote: Roland, I incorporated your srs.db but the translation falls about 30m short (in Melbourne) and about the same distance out at a control point in southern Tasmania.I see you use the National parameters that '... have an estimated accuracy of about 1 metre.' and are most accurate around Canberra (surprise). Geoscience recommend use of their distortion tables (xxx.gsb) for more accurate work Australia-wide. Can you incorporate the parameter reference to the distortion tables in the srs.db? I, like Brett, am out of my depth here. Regards Ken |
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