[Mapcss] MapCSS 0.2 finalization - zoom levels

Thomas Davie tom.davie at gmail.com
Fri May 4 17:13:06 BST 2012

A simple method of fixing this might be to introduce a new property to the canvas element – projection.

Different projections would then pay attention to different zoom condition formats; e.g. if projection:merkator was specified, |z0-... would be expected; while if projection: OSGrid or projection: spherical were used, then |s25000 might be expected.

if (*ra4 != 0xffc78948) { return false; }

On 4 May 2012, at 17:03, Paul Hartmann wrote:

> On 05/01/2012 03:59 PM, Richard Fairhurst wrote:
>> On 01/05/2012 14:47, Paul Hartmann wrote:
>>> In my opinion, it should be the same in MapCSS and the definition of the
>>> zoom selector should be based on map scale rather than on the projected
>>> coordinates in the Mercator projection.
>> My long-term intention for the zoom selector was that "z" would not be
>> the only way of specifying a zoom level, but that we could also have "s"
>> for a standard ratio scale.
>> So:
>> |z14-18        # "900913" zooms 14-18
>> |s25000-50000  # 1:25k to 1:50k
> For a map that is displayed on screen, a scale such as 1:50k is not
> enough, because you usually don't know the monitor resolution.
> We could either use a scale in cm/px directly, or assume some arbitrary
> pixel size, like 0.28 mm.
>> I think we absolutely need to keep the z selector as it is. Otherwise,
>> there is no way to work out what features to include in a simplified
>> database for small-scale rendering, bearing in mind that 900913 maps
>> represent 90% of the webmaps in use today. But offering an alternative
>> for those who want it makes sense to me.
> I see that this simplicity is desirable for a TMS using 900913 (aka
> EPSG:3857).
> But it gets problematic when the map is based on a different projection.
> Are you supposed to replicate the 900913 distortions? This is hard to
> swallow.
> Paul
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