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<div class="Normal"><span style='font-size: 10pt; '>Hi</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>thanks for your answers and
sorry for not replying for approx. 2 months. I will now spend some time on my
problems with grid files. I thought first that the shift grid files can be used
for any reprojection (eg. 21781 to 32632). But it's only usable for one specific
reprojection (defined in the file header). The reprojection is more an
equalization than a "simple" reprojection since the old reference frame
(CH1903/LV03) is inaccurate. By adding the +nadgrid parameter I'm able to
reproject correctly only to one reference system. Reprojections to other systems
are wrong. Is there a way to tell proj4 that it only considers the grid file for
one system?</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>My intention is to use the
grid file for the reprojection of large raster dataset (aerial images) in web
mapping services. I can reproject the whole dataset statically but this approach
doubles the place requirement :( (~300 gigs). And what about other data I serve
via a web mapping service? I'd like a more dynamic way. One solution would be
something like a chain of reprojections: every time I want to reproject from
21781 to 4326 there will be a additional reprojection (21781 -> 2056 ->
4326) in the background. But I have no idea how to do this. </span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>Any help and other ideas are
appreciated!</span><br><span style='font-size: 10pt; '>regards</span><br><span style='font-size: 10pt; '>Stefan</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>> -----Ursprüngliche
Nachricht-----</span><br><span style='font-size: 10pt; '>> Von: Paul Kelly
[mailto:paul-grass@stjohnspoint.co.uk]</span><br><span style='font-size: 10pt; '>>
Gesendet am: Freitag, 23. Januar 2009
16:12</span><br><span style='font-size: 10pt; '>> An: PROJ.4 and general
Projections Discussions</span><br><span style='font-size: 10pt; '>> Betreff:
Re: [Proj] Problems using grid shift
files</span><br><span style='font-size: 10pt; '>>
</span><br><span style='font-size: 10pt; '>> On Fri, 23 Jan 2009, Mikael
Rittri wrote:</span><br><span style='font-size: 10pt; '>>
</span><br><span style='font-size: 10pt; '>> > I think cs2cs normally
assumes that a grid shift file will
</span><br><span style='font-size: 10pt; '>> transform a national datum to
WGS84.</span><br><span style='font-size: 10pt; '>> > So I don't know how
chenyx06.gsb can be used by cs2cs, but
</span><br><span style='font-size: 10pt; '>> perhaps some
pipe</span><br><span style='font-size: 10pt; '>> > construction could be
used.</span><br><span style='font-size: 10pt; '>>
</span><br><span style='font-size: 10pt; '>> Specify the gridshift file as
part of the PROJ.4 description </span><br><span style='font-size: 10pt; '>>
of the CH1903 </span><br><span style='font-size: 10pt; '>> system, and use a
+towgs84=0,0,0 datum parameter set for the CH1903+
</span><br><span style='font-size: 10pt; '>> location. Something along those
lines should work I think, but the
</span><br><span style='font-size: 10pt; '>> co-ordinates would need to be
transformed again to get to
WGS84.</span><br><span style='font-size: 10pt; '>>
</span><br><span style='font-size: 10pt; '>>
Paul</span><br><span style='font-size: 10pt; '>>
_______________________________________________</span><br><span style='font-size: 10pt; '>>
Proj mailing list</span><br><span style='font-size: 10pt; '>>
Proj@lists.maptools.org</span><br><span style='font-size: 10pt; '>>
http://lists.maptools.org/mailman/listinfo/proj</span><br><span style='font-size: 10pt; '>>
</span></div>
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