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I realize I still need to learn much.<br>
Thanks for taking time to explain.<br>
Paolo<br>
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<div class="moz-cite-prefix">Il 07/11/2013 14:59, G. Allegri ha
scritto:<br>
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<div text="#000000" bgcolor="#FFFFFF"> If I understand
well, the datum shift parameters are required in order
to improve the accuracy of the conversion between 3004
and other RS as ED50 UTM33, while they are not needed
for conversion between 102092 and e.g. WGS84?<br>
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<div>The shift parameters are alway needed to obtain higher
precision for CRS trasformations where the datums are
different. When a transform from datum A to datum B is
required, Proj4 (the engine underlying SRS and
projections) does datum A -> WGS84 -> datum B. The
shift parameters (+towgs84) are used my Proj4 to manage
the intermediated transformations to (and from) WGS84,
which is kind of a "pivot CRS".</div>
<div>So, they're should be always employed. 102092 does not
define them, that's why you get worst results.</div>
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<div>giovanni</div>
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