sorry Gabriel...didn´t check my recipients´box and sent it directly to you!
----- Weitergeleitete Message -----
Von: Robert Buckley <robertdbuck...@yahoo.com>
An: Gabriel Roldan <grol...@opengeo.org>
Gesendet: 8:28 Montag, 5.März 2012
Betreff: Re: [Geoserver-users] gwc layer naming convention
Hi,
Thanks for the explanation.
Without having examples, it is pretty difficult to understand the difference
between resolutions, Levels and scales fully.
As a cartographer, I am interested only in the output, ie. if it is disirable
to have a map which shows the following scales - 1:1000.000 / 1:500.000 /
1:250.000 / 1:100.000 / 1:50.000 / 1:25.000 / 1:10.000 / 1:5000 I simply want
to know how to achieve this.
Obviously I would not use "Levels" as this doesn´t give me the control to
choose my own scales. Scale Denominators and Resolutions let me acheive this.
If using Resolutions is the recommended way, would you be able to explain, ( or
give a tutorial url) how I can accurately calculate the resolutions from a
given coordinate system? (and a given extent if this is relevent?)
eg. If I am using ETRS89 defined as follows...
<gridSet>
<name>EPSG:25832</name>
<srs><number>25832</number></srs>
<extent>
<coords>
<double>226014</double>
<double>5648111</double>
<double>773840</double>
<double>5998111</double>
</coords>
</extent>
Using these extents I can workout that the width west to east is 5998111
- 5648111 = 350000 meters and the hight is 773840 - 226014 = 547826
meters...but this has no real use as far as I can tell as the resolution
depends on only unit of measurement and screen dpi. Is this right?
Using a DPI of OpenLayers.DOTS_PER_INCH = 25.4 / 0.28 = 90.71428571428571,
and 39.3700787 inches in a meter of screen I can then workout that....
Resolution = chosen scale / InchesPerUnit * DPI
therefore...
Res = 1000000 / (39.2701 * 90.71428571428571)
R =1000000 / 3562.359071428571260271
R = 280.712859077111976006937033
the resolution corresponding to 1:1000.000 for a coordinate system defined in
meters is 280.712859077 etc
Is this the correct method of working out the resolutions? It would mean that
these resolutions are universal for all coordinate systems which use meters as
a unit.
I defined my geowebcache.xml using scaledenomintors. By looking into the source
code of the openlayers geowebcache demo the following resolutions are defined
for the above scales...
280.0, 140.0, 70.0, 27.999999999999996, 13.999999999999998, 6.999999999999999,
2.8, 1.4
they are close...but not identical...
280.712859etc, 140.356429etc, 28.0712859etc, 2.80712859, 1.4035642953
To how many decimal places should the resolutionsbe rounded, and why is
geoserver defining the first resolution as 280.0 and not 280,712 etc
Thanks for any comments...I´m sure there are lots of other users who have
exactly the same questions...
yours,
Rob
________________________________
Von: Gabriel Roldan <grol...@opengeo.org>
An: Robert Buckley <robertdbuck...@yahoo.com>
CC: "geoserver-users@lists.sourceforge.net"
<geoserver-users@lists.sourceforge.net>
Gesendet: 22:00 Sonntag, 4.März 2012
Betreff: Re: [Geoserver-users] gwc layer naming convention
On Sat, Feb 18, 2012 at 9:45 AM, Robert Buckley <robertdbuck...@yahoo.com>
wrote:
Thanks Gabriel,
>
>
>at last last i´ve got GWC working with custom scales!...the bit that wasn´t
>really very well documentated was the crucial last bit with the
><wmslayers>....Now it´s working I understand the principle much better.
cool.
>
>
>
>I am now looking at the XML schema regarding "resolutions",
>"scaleDenominators", or "levels".
>
>
>I have seen now custom geowebcache.xml examples which define either levels or
>scaleDenominators. Is there a reason for this..
There is. Levels gives you the easiest way of defining the gridset at the
expense of flexibility, like in gwc will just take the whole gridset bounds and
calculate each level's resolution as (level -1) * 2.
scaleDenominators and resolutions lets you specify exactly how you want each
zoom level. Resolutions is the recommended way, as it's not based on a fixed
world to pixel ratio. But some want to define them based on scale denominators
instead (there are a couple of them in the TMS spec), as it's common to have
1/1M, 1/500K, etc maps. Chosing which one to preserve also lets you choose
which one is bound to floating point rounding errors.
or do all methods of defining map levels work equally well?
They should work equally well (provided you use a recent gwc version, 1.2.6 I
think still has a bug that prevents using levels).
Cheers,
Gabriel
>
>thanks again,
>
>
>Rob
>
>
>
>________________________________
> Von: Gabriel Roldan <grol...@opengeo.org>
>An: Robert Buckley <robertdbuck...@yahoo.com>
>Cc: "geoserver-users@lists.sourceforge.net"
><geoserver-users@lists.sourceforge.net>
>Gesendet: 22:36 Freitag, 17.Februar 2012
>Betreff: Re: [Geoserver-users] gwc layer naming convention
>
>
>
>
>
><wmsLayer>
>...
><name>basemap</name>
><wmsUrl><string>SERVERPATH/wms?</wmsUrl>
><wmsLayers>ocean,border,river,landcover</wmsLayers>
></wmsLayer>
>
>On Fri, Feb 17, 2012 at 5:55 PM, Robert Buckley <robertdbuck...@yahoo.com>
>wrote:
>
>Hi,
>>
>>
>>I´m just reading through the geowebcache documentation, and don´t quite
>>understand something about the naming of layers in geowebcache.xml.
>>
>>
>>
>>
>>"<name> The layer name as published by GeoWebCache. It can be the same name
>>as known to the WMS (for example, in GeoServer, this would
>>benamespace:layername) or not."
>>
>>
>>If the layername is something different from the wms layer, how can gwc know
>>which layer is to be displayed by gwc?
>>
>>
>>
>>eg. I have a layer named zgb:Grenzen_ZGB.
>>
>>
>>the wms url is
>>.....SERVERPATH/wms?service=WMS&version=1.1.0&request=GetMap&layers=zgb:Grenzen_ZGB
>>
>>
>>geowebcache reads this from the wms url and creates a gwc tiled
>>representation.....so if the layername is something different, how can gwc
>>know which layers is to be tiled?
>>
>>
>>
>>
>>furthermore....can anyone tell me why I would first define a layer with
>><wmslayer> etc....and then again in the <wmslayers> section? Is this for
>>configurations which span more than just one layer?
>>
>>
>>
>>
>>thanks,
>>
>>
>>Rob
>>
>>
>>------------------------------------------------------------------------------
>>Virtualization & Cloud Management Using Capacity Planning
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>>also focuses on allowing computing to be delivered as a service.
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>>
>>
>
>
>
>--
>Gabriel Roldan
>OpenGeo - http://opengeo.org
>Expert service straight from the developers.
>
>
>
>------------------------------------------------------------------------------
>Virtualization & Cloud Management Using Capacity Planning
>Cloud computing makes use of virtualization - but cloud computing
>also focuses on allowing computing to be delivered as a service.
>http://www.accelacomm.com/jaw/sfnl/114/51521223/
>_______________________________________________
>Geoserver-users mailing list
>Geoserver-users@lists.sourceforge.net
>https://lists.sourceforge.net/lists/listinfo/geoserver-users
>
>
--
Gabriel Roldan
OpenGeo - http://opengeo.org
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