[MetaCRS] question on GeoTiff axis order

[Frank Warmerdam]

On 10-12-17 11:43 AM, Martin Desruisseaux wrote:
> Hello Frank
>
> Thanks for your reply. I guess that "correct way" means "what the GeoTIFF
> standard said", and that standard at
> http://www.remotesensing.org/geotiff/spec/geotiff2.5.html seems to be silent
> about the axis order. The above page basically just make a reference to a list
> a tables, and the GeoTIFF table at
> ftp://ftp.remotesensing.org/geotiff/tables/horiz_cs.csv explicitely define
> (lat,long) axis order for 4326 and some other CRS.
>
>  From this point of view, the GeoTIFF specification seems to mandate (lat,long)
> axis order. I guess that this is not the intend. Maybe a note somewhere could
> at least put a warning (something like "while the GeoTIFF tables derived from
> the EPSG database put latitude before longitude, the common usage for raster
> data is to display north up and east on the right side"). While I admit that
> this is very fuzzy, it is actually hard to provide an accurate rule applicable
> also to polar area, South Africa, Australia, etc..., and I guess that no one
> have the energy to produce an accurate specification at this time...

Martin,

My approach is to assume long/lat for geographic coordinate systems, but
(in theory at least) to honour EPSG axis order for projected coordinate
systems.  In theory, as the spec does not address axis order, you are right
that we ought to treat most GCSes as lat/long but the absolutely foolhardyness
of going against all current practice makes this unreasonable.  My emotional
response is largely due to the mayhem I saw come out of pushing EPSG axis
order for GCSes in WMS and beyond.

I agree that some clarification in the GeoTIFF FAQ would be helpful.  I
will endevour to add something there today.

I'm cc:ing the geotiff list since that is really where this discussion
should be. For those there who are interested the exchange is available
at:

   http://lists.osgeo.org/pipermail/metacrs/2010-December/thread.html

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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