Dear Frank,<br><br>thanks a lot for your prompt assistance!<br><br>br,<br><br>ilumas<br><br><br><br><div class="gmail_quote">On Wed, Apr 21, 2010 at 7:13 PM, Frank Warmerdam <span dir="ltr"><<a href="mailto:warmerdam@pobox.com">warmerdam@pobox.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div><div></div><div class="h5">Ilumas wrote:<br>
> Dear list,<br>
><br>
> could you kindly confirm that the cs2cs's +towgs84 parameters remain the<br>
> same for a certain datum regardless of the direction of the<br>
> transformation. Some people (e.g.<br>
> <a href="http://n2.nabble.com/Datum-Shift-WGS84-to-Arc1960-not-working-propberly-td3410479.html" target="_blank">http://n2.nabble.com/Datum-Shift-WGS84-to-Arc1960-not-working-propberly-td3410479.html</a>)<br>
> <<a href="http://n2.nabble.com/Datum-Shift-WGS84-to-Arc1960-not-working-propberly-td3410479.html" target="_blank">http://n2.nabble.com/Datum-Shift-WGS84-to-Arc1960-not-working-propberly-td3410479.html</a>>seem<br>
> to suggest that the values need to be negated when going FROM wgs84 TO<br>
> something else, but this seems a bit strange to me. Unfortunately all<br>
> the examples in the man pages seem to be about changing the coordinates<br>
> TO wgs84...<br>
<br>
</div></div>Ilumas,<br>
<br>
The parameters are always expressed in terms of what it takes to transform<br>
to WGS84. If PROJ is transforming from WGS84 it will internally reverse<br>
the sense of the transformation.<br>
<br>
Keep in mind there is also an issue with the handedness of the parameters.<br>
Some folks, mostly european, express the parameters with a different<br>
handedness. The scripts that generate the "epsg" init file already know<br>
about this case and convert to the usual PROJ.4/North American handedness<br>
but if you are researching parameters yourself from various sources you<br>
may need to be aware of it.<br>
<br>
Best regards,<br>
<font color="#888888">--<br>
---------------------------------------+--------------------------------------<br>
I set the clouds in motion - turn up | Frank Warmerdam, <a href="mailto:warmerdam@pobox.com">warmerdam@pobox.com</a><br>
light and sound - activate the windows | <a href="http://pobox.com/%7Ewarmerdam" target="_blank">http://pobox.com/~warmerdam</a><br>
and watch the world go round - Rush | Geospatial Programmer for Rent<br>
</font><div><div></div><div class="h5"><br>
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