How would I check this.<br><br><div><span class="gmail_quote">On 11/14/05, <b class="gmail_sendername"><a href="mailto:strk@refractions.net">strk@refractions.net</a></b> <<a href="mailto:strk@refractions.net">strk@refractions.net
</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">None of the measurement functions in postgis take projection into<br>account. Computations are purely cartesian. Can it be that the
<br>input (shapefile) is really in decimal degrees and it is transformed<br>(reprojected) to GDA94/MGA84 during ARC load ?<br><br>--strk;<br><br>On Mon, Nov 14, 2005 at 08:25:54PM +1100, Johan Wehtje wrote:<br>> isvalid returns true, envelope gives results that make no sense outside of
<br>> the world of Lilliput.<br>><br>> I had some of the same maps but with MGA 84 zone 56 datum, and they have<br>> loaded no problem, I therefore think that the definition for the GDA94<br>> spatial refernces must be out of whack, because the shape files have no
<br>> problem when loaded in arc view in either GDA 94 or MGA 84.<br>><br>> The GDA 94 shapes have attached xml files, and the pojection string in these<br>> does look the same as the proj4 text in the Spatial Refsys table, so I don't
<br>> know what is going wrong.<br>><br>> Cheers<br>> (and thanks your help)<br>> Johan Wehtje<br>><br>> On 11/14/05, <a href="mailto:strk@refractions.net">strk@refractions.net</a> <<a href="mailto:strk@refractions.net">
strk@refractions.net</a>> wrote:<br>> ><br>> > Does the area computation give acceptable value for the geometry's<br>> > envelope ? [ select area(envelope(the_geom)) ] ?<br>> > Is the geometry valid ? [ select isvalid(the_geom) ] ?
<br>> ><br>> > --strk;<br>> ><br>> > On Mon, Nov 14, 2005 at 07:50:10PM +1100, Johan Wehtje wrote:<br>> > > I am using Postgis 1.0.4 on Win XP with Postgresql 8.1.<br>> > ><br>> > > I had some Shape files that have Land Parcels , they use GDA94 Zone 56 (
<br>> > > srid 28356) , and I used shp2pgsql to load them into my DB.<br>> > ><br>> > > But when I an area calculation I get results that are completely wrong ,<br>> > and<br>> > > when i add a Postgis layer using QGIS the scale would have me beleive
<br>> > that<br>> > > the entire shire (which about 80 km accross) is about 2 cm.<br>> > ><br>> > > I have tried this about twenty times, on 2 different machines - and the<br>> > > results are the same. i have verified the original shape files in
<br>> > Arcview,<br>> > > and when they are laoded the scale and area are all what they should be.<br>> > ><br>> > > What am I doing wrong?<br>> > ><br>> > > Johan Wehtje
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