Yes, we realize that's an issue. In our case we're only concerned with a
relatively small area (the province of BC), so the variation in true scale
across the area is not that large (around 20%). We realize that we won't
get 100% correlation, but we'd like to at least get it looking right better
than 50% of the time!
The issue is that it's very hard to determine what a scale limit in a SLD
corresponds to in terms of client (true, screen) scale. It seems odd that
the GeoServer scale would be a factor of 2 or more different to the true
(image) scale.
There does appear to be a rough correlation, which may even be a linear
factor. But it's hard to tell without seeing the exact scale that
GeoServer is using in its SLD algorithm.
As examples, here's some scale limits from SLDs, with the corresponding
largest client scale (approximate) at which the layer is visible
SLD Client Zoom Level
10,000,000 4,399,000 6
6,000,000 2,297,000 7
2,000,000 565,000 9
1,000,000 282,000 10
500,000 143,000 11
20,000 8,957 15
On Mon, Feb 15, 2016 at 2:35 PM, Rahkonen Jukka (MML) <
[email protected]> wrote:
> Hi,
>
>
>
> I am not sure if I understood the problem but I wonder how the true scale
> suits together with Web Mercator. I guess that you do not expect that the
> tiles of the same zoom level would use different styles at equator than in
> Canada or Finland even the true scale differs a lot.
>
>
>
> -Jukka Rahkonen-
>
>
>
> Martin Davis wrote:
>
>
>
> We are displaying map images in Web Mercator, from a GeoServer with native
> CRS as BC-Albers (EPGS:3005).
>
>
>
> We are using an OpenLayers client to display the map images. We have
> confirmed that the geodetic scale displayed by OpenLayers is approximately
> the true scale of the map images (modulo the fact that OL uses a fixed
> resolution of 72 DPI).
>
>
>
> Based on the zoom levels at which layers become visible, it appears that
> GeoServer's internal computed scale is from 2 to 4 times larger than the
> client scale.
>
>
>
> Is this expected?
>
>
>
> Is there any way to determine a way to map between client scale and
> Geoserver scale, so that we can configure the client to track GeoServer
> visibility faithfully?
>
>
>
> Is there any way to display the internal GeoServer scale to make it
> possible to confirm if this analysis is correct?
>
>
>
>
>
> GeoServer ver 2.6 (although I believe this is happening in 2.8 as well)
>
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