[OpenLayers-Users] Users Digest, Vol 4, Issue 22

["RIVIERE Robert - CETE Méditerr./DI/ETER"]

Oups I'm sorry, of course 10 minutes after posting this I'v discovered that
there is now a WMS.untiled in openlyers 2.0.

Thanks,

Robert Rivière

-----Message d'origine-----
De : RIVIERE Robert, CETE Méditerr./DI/ETER 
Envoyé : mardi 29 août 2006 11:20
À : 'users at openlayers.org'
Cc : RIVIERE Robert, CETE Méditerr./DI/ETER
Objet : RE: Users Digest, Vol 4, Issue 22


Hello,

it's the first time I'm  posting to this mailist but I've been following
discussions for several months.
I'm working for a big administration where we've built in last months an
infrastructure of WMS servers.
OpenLayers seems to be quite interesting to use as a WMS client,
congratulations for this very nice work.

But when trying to use it, I've found the same problems that have been
discussed earlier this month :

- on the fly reprojection : if my server's original data are not it
EPSG:4326, requested tiles are generated after a reprojection by the server.
But as Arnd Wippermann mentionned, "A square in one projection is not a
square in the other projection", so data present in a square tile are not
coming from a square initial region. The result is that when you are gluing
tiles together, they dont match on borders, pieces of territories are
repeated on several tiles, etc...

- dynamic labelling : in my case, the server is MapServer in WMS mode.
MapServer tries to optimize labelling placement in a requested view. If you
are using several tiles, mapserver will try to place labels in each tile,
and the final result will be messy (typically, labels will be repeated in
several tiles)

So I'm asking if anyone has found a workaround for these problems. I'm not
sure there could be any... Except not using tiling and configure openlayers
to display only 1x1 image (is it possible without heavy modifications ?).

Thanks,

Robert Rivière

--- original message ---

Date: Wed, 23 Aug 2006 21:08:08 +0200
From: "Arnd Wippermann" <arnd.wippermann at web.de>
Subject: Re: [OpenLayers-Users] WMS overlay alignment on Google Map
	baselayer
To: <users at openlayers.org>
Message-ID: <E1GFy6Y-0000ua-00 at smtp05.web.de>
Content-Type: text/plain;	charset="iso-8859-1"

Hello,

I have some problems to understand the discussion. 

To get tiles from any data provider I have to use the projection the data
provider supports. For WMS the BBOX must contain values, which lie in this
projection. 

When I use a projection in OpenLayers, which is not supported by the data
provider, I'm not able with reprojection of the BBOX-values to get the
correct tiles. A square in one projection is not a square in the other
projection. 

Therefor I must use a mapserver (when the data provider, who often support
various projections,  not support the projection I want), which is able to
reproject data and send back the correct distorted (to the original
projection of the data provider) image to OpenLayers. I have to use a
program (mapserver), which is able to distort images. With Javascript there
is no possibly to do this.

When I'm wrong, please some clues so I can follow the discussion.

Mit freundlichen Gr?ssen

Arnd Wippermann
http://gis.ibbeck.de/pinguinale/