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

Dylan Beaudette dylan.beaudette at gmail.com
Mon Jul 31 20:43:28 EDT 2006


Ed - 

I agree completely - The user is responsible for how he/she chooses to 
use/mis-use the software. 

Perhaps I as asking for something (that most of us don't want for the stated 
reasons) but which is worth mentioning when someone is getting started. Maybe 
a couple good mistakes are a better reminder than a casual notice from  the 
software.

Cheers,

Dylan

On Monday 31 July 2006 17:10, Ed McNierney wrote:
> Dylan -
>
> I understand the concern, but I agree with Frank on the implementation
> issues.  May I suggest that another approach would be to avoid the
> "default" behavior and require an explicit statement by the user of the
> datum shift method to be used?  I realize that backward compatibility
> requires accepting current transformations "as is", but a statement
> like:
>
> ogr2ogr -s_srs 'prj=latlong datum=NAD83' -t_srs '+proj=utm +zone=11
> +datum=NAD27 +method=NADCON' output.shp input.shp
>
> Might help avoid any mystery about what "default" behavior is.  A
> compile-time "strict" option might be required to turn this feature on.
>
> I don't think that a command like the one above should warn the user
> that a datum shift is being performed, any more than the user should be
> warned that the coordinates of the points will be projected.  The
> command line asks for a datum shift, so the user shouldn't be surprised
> if one is performed.
>
> 	- Ed
>
>
> Ed McNierney
> President and Chief Mapmaker
> TopoZone.com / Maps a la carte, Inc.
> 73 Princeton Street, Suite 305
> North Chelmsford, MA  01863
> Phone: +1 (978) 251-4242
> Fax: +1 (978) 251-1396
> ed at topozone.com
>
> -----Original Message-----
> From: gdal-dev-bounces at lists.maptools.org
> [mailto:gdal-dev-bounces at lists.maptools.org] On Behalf Of Dylan
> Beaudette
> Sent: Monday, July 31, 2006 4:41 PM
> To: gdal-dev
> Subject: [Gdal-dev] issue warning to user when performing datum shift
> (OGR,GDAL)
>
> Hi everyone,
>
>
> In light of some recent thought, experimentation, and discussion [1] I
> am wondering if it would be at all possible or even desirable to warn
> the user when a datum shift operation is about to be performed. Within
> the US, and assumming that the NADCON grid was installed with Proj4,
> transforming between NAD27 and NAD83 should work just as expected.
> However, in other parts of the world, this may not be the case.
> Therefore, it might be a good idea to follow the model used in GRASS,
> where the user is specifically prompted for datum transform parameters
> whenever defining a new locatio, in these situations.
>
> Any thoughts / reasons not to do this?
>
> Cheers,
>
> 1. http://casoilresource.lawr.ucdavis.edu/drupal/node/259
>
>
> Dylan
> _______________________________________________
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> Gdal-dev at lists.maptools.org
> http://lists.maptools.org/mailman/listinfo/gdal-dev

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



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