[Gdal-dev] issue warning to user when performing datum shift (OGR, GDAL )

[Dylan Beaudette]

On Tuesday 01 August 2006 11:02, Matt Wilkie wrote:
> > I agree completely - The user is responsible for how he/she chooses to
> > use/mis-use the software.
>
> So if I understand this correctly, the summary of repsonses is: this is
> a logical bug rather than functional one, and the fix is not
> implementation but documentation.
>
I would agree.

> The first comment from Paul K on the CA Soils site would be a good
> "patch", reproduced here and heavily edited:
>
>     There is no such thing as an accurate "default" set of datum
> transformation parameters for a datum. OGR uses (NADCON) by default,
> which is the most accurate available for North America, but in the
> general case (worldwide) this is very hard to determine and there
> normally is no such thing as a default. The transformation that should
> be used depends on the exact area covered, accuracy required etc. In
> other words, user beware and do your homework.
>     -- http://casoilresource.lawr.ucdavis.edu/drupal/node/259

Wording is concise and to the point.

> I'm not sure where in the docs this warning should go though. The OGR
> Projections Tutorial (http://ogr.maptools.org/osr_tutorial.html) is
> likely to be avoided by end users as it's about how to code projection.
> Perhaps the cs2cs man page? http://proj.maptools.org/man_cs2cs.html
>
> cheers,

I feel that this "reminder" should find its way into the docs somewhere, but 
other than possibly a very general README or the like, it would be a little 
out of place.

Just to reiterate, I am not suggesting that we dumb down the powerfull, and 
often non-interactive tools that we use and love. However, I think that a 
carefully placed reminder might save a new user from a bit of grief- and at 
the same time promote the idea that people must fully _understand_ their data 
and what they are _doing_ to it.

Cheers,


-- 
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341