Well, I agree that for assessing the accuracy of the re-projection results one needs a reference, but that should not be necessary for understanding the behavior of the cs2cs or the towgs84 string. Therefore I still argue that the test I suggested below is a valid way to test whether the parameter values need to be negated or not. Anyone?<div>
<br></div><div>ilumas<br><br><div class="gmail_quote">On Fri, Apr 23, 2010 at 3:39 PM, Jean-Claude REPETTO <span dir="ltr"><<a href="mailto:jrepetto@free.fr">jrepetto@free.fr</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Le 23/04/2010 14:24, Ilumas a écrit :<br>
<div class="im">><br>
> Anyway, I believe that the behaviour of a certain towgs84 string is easy<br>
</div>> to test with cs2cs itself: just do the transformation to one direction<br>
<div class="im">> (e.g. from WGS84) and convert the resulting coordinates back to the<br>
> original datum using exactly the same parameter string. If the resulting<br>
> coordinates equal to the original ones, no negation is needed. Right?<br>
><br>
> ilumas<br>
<br>
</div>Hi,nding the behavious of the cs2cs<br>
<br>
I think you are wrong. To check the parameters, you need to know the<br>
coordinates of at least one point in both datums, and compare them with<br>
the results of cs2cs.<br>
<font color="#888888"><br>
Jean-Claude<br>
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