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Re: [udig-devel] wmt distortion
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Actually because we had so much fun with these calculations we ended up leaving it up to each renderer to look at its data source and advertise a Set<Range<Double,Double>> of valid scales; for most source of data this is easy; for the tiled data sources this ends up being the list of scales for which tiles are defined.
So there is the opportunity to communicate with uDig what scales are defined; even if the source has a slightly different idea of what is going on. For the tiled servers they tend to communicate the resolutions at which they have data available. The scale to resolution conversation is where (I guess) the fun is.
Jody
On 05/10/2010, at 4:50 PM, Andrea Aime wrote:
> On Tue, Oct 5, 2010 at 8:35 AM, Jody Garnett <jody.garnett@xxxxxxxxx> wrote:
>> We did update the renderer interface so that tiled data sources could
>> indicate specific zoom levels; that is what the zoom level switch should be
>> picking up on?
>> I am not sure if this information is referenced by the default zoom in and
>> zoom out buttons or not? (It may of just been done for a commercial project
>> emily was working on).
>> I remember there being a bit of a gap between switching zoom level based on
>> scale; vs using the exact resolutions defined by the tile servers. So yes I
>> imagine that testing would be very helpful as we take on more tile servers?
>
> I'm wondering if this has anything to do with the many different ways to compute
> a scale. The OGC defined a simplified expression to compute the scales in
> SLD that is implemented by many WMS servers (but not all, some participants
> to the shootout had to fix their way to compute the scale) and afaik uDig is
> using an accurate scale computation instead of the OGC suggested one.
>
> This might explain the differences you're seeing. Or it might be something else
> entirely... not sure what exactly goes on there :-p
>
> Cheers
> Andrea
>
> -----------------------------------------------------
> Ing. Andrea Aime
> Senior Software Engineer
>
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>
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