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

Daniel Morissette dmorissette at mapgears.com
Tue Jul 24 14:22:19 PDT 2018

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 All we find in the spec is a mention (in 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.


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 mailing list
> mapserver-dev at lists.osgeo.org
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Daniel Morissette
Mapgears Inc
T: +1 418-696-5056 #201

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