[mapserver-dev] Scale computations for non-square pixels...

[Lime, Steve D (MNIT)]

The current approach assumed square cells (way back in the 1990's) so x, y or diagonal didn't matter. ;-)

-----Original Message-----
From: mapserver-dev [mailto:mapserver-dev-bounces at lists.osgeo.org] On Behalf Of Daniel Morissette
Sent: Tuesday, July 24, 2018 4:22 PM
To: mapserver-dev at lists.osgeo.org
Subject: Re: [mapserver-dev] Scale computations for non-square pixels...

Since you asked for feedback...

I had a look at the WMS 1.3 spec looking for guidance on this question 
and don't see a clear mention of whether the scaledenom should be based 
on the x, y or diagonal pixel size. The spec seems to assume square 
pixels for scaledenom witout being explicit about it (section 
7.2.4.6.9). All we find in the spec is a mention (in 7.3.3.8) that if 
WIDTH and HEIGHT don't match that will result in non-square pixels, but 
the spec does not address the impact on the scaledenom.

Personally I'd be tempted to go with scale based on the diagonal cell 
size just because that would be more or less an average of the x and y 
scales, so one would think it should work fine in more cases. However I 
could be mistaken since I don't know the reasons why the current 
approach was selected originally.

Daniel


On 2018-07-24 11:22 AM, Lime, Steve D (MNIT) wrote:
> Hi all: We have a ticket out there regarding scale computation with 
> non-square pixels (see 
> https://github.com/mapserver/mapserver/issues/5625). It should be easy 
> to implement a fix, to the extent it’s possible to come up with a single 
> scale value when that’s
> 
> really not the case. Any opinions on what a “best” approach would be? 
> --Steve
> 
> 
> 
> _______________________________________________
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> mapserver-dev at lists.osgeo.org
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> 


-- 
Daniel Morissette
Mapgears Inc
T: +1 418-696-5056 #201
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