[Gdal-dev] projected bounding box

Ed McNierney ed at topozone.com
Mon Jul 14 13:03:57 EDT 2003

Jonathan -

Sorry - your first message made it sound like a specific application.  If you're building a general-purpose tool, you need to solve the general case <g>.  If you need to handle arbitrary map scales and projections, I can't think of way to select a good buffer value automatically (or at least, not a way that would be easier than projecting along the entire line).

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
ed at topozone.com
(978) 251-4242 

-----Original Message-----
From: Jonathan Coles [mailto:jonathan at intevation.de]
Sent: Monday, July 14, 2003 12:52 PM
To: gdal-dev at remotesensing.org
Subject: RE: [Gdal-dev] projected bounding box

On Mon, 2003-07-14 at 18:39, Ed McNierney wrote:
> This is a tricky problem to solve in a general case, 
> and has been the source of a number of software bugs 
> I've met along the way!

Hopefully, in the future, not with Thuban ;)

> To do it right, you need to take EACH POINT along
> each of the edges of the output bounding box (rectangle)
> and reproject it back into the source projection.  For 
> each edge you calculate the appropriate minimum/maximum 
> value in the input projection.

I was afraid of this response.

> it might be easier for you to take your specific application and calculate
> a "buffer" value.  
> This is obviously a special-case solution, but it's 
> probably a lot simpler and faster than trying to solve 
> the general problem.

That's the problem, this isn't a special case situation. It should
really work with any projection anywhere on the globe. It certainly is
something for me to think about though. Perhaps I can come up with a way
that will guarantee a good buffer value. Thanks for your thoughts.


 Jonathan Coles                                jonathan at intevation.de
 Intevation GmbH                             http://www.intevation.de

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