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

Matt Wilkie matt.wilkie at gov.yk.ca
Tue Aug 1 14:02:19 EDT 2006

> 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.

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

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


matt wilkie
Geographic Information,
Information Management and Technology,
Yukon Department of Environment
10 Burns Road * Whitehorse, Yukon * Y1A 4Y9
867-667-8133 Tel * 867-393-7003 Fax

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