[Proj] cs2cs's +towgs84 usage

[Ilumas]

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?

ilumas

On Fri, Apr 23, 2010 at 3:39 PM, Jean-Claude REPETTO <jrepetto at free.fr>wrote:

> Le 23/04/2010 14:24, Ilumas a écrit :
> >
> > Anyway, I believe that the behaviour of a certain towgs84 string is easy
> > to test with cs2cs itself: just do the transformation to one direction
> > (e.g. from WGS84) and convert the resulting coordinates back to the
> > original datum using exactly the same parameter string. If the resulting
> > coordinates equal to the original ones, no negation is needed. Right?
> >
> > ilumas
>
> Hi,nding the behavious of the cs2cs
>
> I think you are wrong. To check the parameters, you need to know the
> coordinates of at least one point in both datums, and compare them with
> the results of cs2cs.
>
> Jean-Claude
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