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On 22-1-2010 15:40, Mikael Rittri wrote:
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cite="mid:FAF6E56B26D2044696772EBE89B1535101BDE7F4@posty.carmenta.se"
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<div dir="ltr" align="left"><span class="131363214-22012010"><font
face="Arial">Jan, you wrote </font></span></div>
<div dir="ltr" align="left"><span class="131363214-22012010"></span> </div>
<div dir="ltr" align="left"><span class="131363214-22012010">> </span>All
my observations about the towgs parameters have been tested with real
Belgian coordinates overlaid over Google.</div>
<div dir="ltr" align="left"> </div>
<div dir="ltr" align="left"><span class="131363214-22012010"><font
face="Arial">Fine. But if you did make an error when transcribing the
newer transforms into Proj.4 syntax, and </font></span></div>
<div dir="ltr" align="left"><span class="131363214-22012010"><font
face="Arial">the error was just in the rotation angles, then the </font></span><span
class="131363214-22012010"><font face="Arial">effect may be too small
to notice. </font></span></div>
<div dir="ltr" align="left"><span class="131363214-22012010"></span> </div>
<div dir="ltr" align="left"><span class="131363214-22012010"><font
face="Arial">I mean, the angles describe a rotation, so there is
presumably a fixed point in Belgium where </font></span></div>
<div dir="ltr" align="left"><span class="131363214-22012010"><font
face="Arial">the rotation has no effect. If your test points happened
to be near the fixed point, the </font></span></div>
<div dir="ltr" align="left"><span class="131363214-22012010"><font
face="Arial">effect of the reversed angle signs could be very small. </font></span></div>
<div dir="ltr" align="left"><span class="131363214-22012010"></span> </div>
<div dir="ltr" align="left"><span class="131363214-22012010"><font
face="Arial"><font face="Times New Roman">> As I said before, the
EPSG database is not very systematical in the way it represents its
formulas, </font></font></span></div>
<div dir="ltr" align="left"><span class="131363214-22012010"><font
face="Arial"><font face="Times New Roman">> it just takes them from
whatever source is available, untested AFAIK. Never use them without
testing them with real world coordinates.</font></font></span></div>
<div><span class="131363214-22012010"></span> </div>
<div><span class="131363214-22012010"><font face="Arial">I agree
completely. But I am not yet convinced that you are right and EPSG
wrong for the newer transforms,</font></span></div>
<div><span class="131363214-22012010"><font face="Arial">although
that is certainly possible. Do you have some link to the offician
Belgian documents? </font></span><span class="131363214-22012010"></span></div>
<div dir="ltr" align="left"><font face="Arial"><br>
</font></div>
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As I said in a previous email:<br>
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<a class="moz-txt-link-freetext" href="http://www.ngi.be/FR/FR4-4.shtm">http://www.ngi.be/FR/FR4-4.shtm</a><br>
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