[josm-dev] WMS layers default to "automatically change resolution"

[Martin Koppenhoefer]

2013/6/10 Stefan Breunig <breunig at uni-hd.de>

> > The problem is that some servers we are using
> > here might block you if you do too many requests in a short period of
> > time,
>
> The zoom snaps to certain resolutions to make caching work. Zooming out
> probably saves some requests because you need less tiles/images to fill
> your screen. Zooming in doesn’t, but then again I didn’t use high zoom
> levels very often in my practical tests. If you aren’t annoyed by this
> feature and only disable it out of fear to be rate-limited by your WMS,
> can you try it in every day use?



Usually I go to a zoom level (around 50 meters indicated in the scale in
the upper left corner of the screen) and remain there (this seems to
guarantee to have native resolution). This value has been tested by trial
and error and seems to guarantee "full" resolution of the server we are
accessing to.

We are using this
http://wms.pcn.minambiente.it/ogc?map=/ms_ogc/wms_v1.3/raster/ortofoto_colore_06.map
and this :
http://wms.pcn.minambiente.it/ogc?map=/ms_ogc/wms_v1.3/raster/ortofoto_colore_08.map
(has slightly higher resolution)
but I also don't know how to get the actual resolution of the imagery
behind.

I haven't been blocked recently by this server, but I am aware of some
other Italian mappers who access this with a fix IP, and they had serious
problems after being banned (they had traced e.g. railroads or rivers or
other features that imply the download of a lot of tiles compared to
tracing features like buildings in a relatively compact area. I agree that
this is mainly a problem of the provider's policy of this particular WMS
and not a general obstacle to change the JOSM defaults.

On slow servers the current default still seems to have other disadvantages
(it becomes even slower when you have to download several resolutions
instead of one, and I also don't see an advantage in using fewer than the
best resolution.



> Alternatively relay the WMS server
> details to me, so I can try. I believe having this default-on is more
> sensible, but only if it doesn’t turn out to be a problem.
>





> I had a look at the WMS specification when implementing this and found
> nothing of relevance to get the “native resolution” or available
> pre-rendered ones.  I had a look at some WMS servers if there’s maybe a
> non-standard way of including this, but I didn’t find anything. Take
> the map4bw server, for example. It definitely has resolution
> information[1] but it’s not included in the WMS file[2].
>
> Best regards,
> Stefan
>



Best regards,
Martin