[Geotiff] [MetaCRS] question on GeoTiff axis order

[Max Martinez]

Frank,

Your approach does sound reasonable. The horse has long left the barn on
this one.

But I'm not sure I completely understand what Martin is getting at.
GeoTIFF doesn't address display of the image, only the definition of
raster space, model space and the relationship between the two. The way
I would interpret this is that implementers are not intending to change
the definition of the coordinate reference systems used from EPSG.
Rather, lack of specificity in the standard, some misleading examples
(e.g. , 3.2.1), and old habit has led to common usage of fixing the axis
order of geographic coordinate systems at Lon, Lat when specifying the
relationship between raster space and model space, regardless of the CRS
definition. This only affects the encoding of the tags that describe
this relationship (ModelPixelScaleTag, ModelTiepointTag,
ModelTransformationTag) and adopters would be advised to observe this
convention if they want to achieve interoperability.

Perhaps this has an impact elsewhere and I am overlooking it.

Max

-----Original Message-----
From: geotiff-bounces at lists.maptools.org
[mailto:geotiff-bounces at lists.maptools.org] On Behalf Of Frank Warmerdam
Sent: Friday, December 17, 2010 12:15 PM
To: metacrs at lists.osgeo.org
Cc: GeoTIFF
Subject: Re: [Geotiff] [MetaCRS] question on GeoTiff axis order

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,
-- 
---------------------------------------+--------------------------------
---------------------------------------+------
I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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