[mapserver-users] mapserver architecture for multi-websites on several machines

[Dave McIlhagga]

Hi Claudia, John,

We have been working closely with Steve Lime to complete the integration
of the OpenGIS Consortium (OGC) Web Map Server (WMS) capabilities into
MapServer.  Like John, I would strongly recommend the use of WMS for
this type of project as it fits precicely the scenario that you have
outlined below.

Just for clarity, WMS specifications outline three functions for
standard communications among servers:

Get Capabilities
Get Map
Get Feature Info

If I'm not mistaken, I believe these are all requested through http
requests.

Get Capabilities allows a server to ask a WMS MapServer information such
as version compliance, layers availability, etc...  This is used to make
further requests for the map and attribute information.

Get Map returns a map based on information passed as parameters.  This
includes projection info, extents, selected layers, etc...  At this time
symbology is not included so this has to be prepared beforehand.

Get Feature Info returns attribute information for a selected point and
selected layer(s) in XML format.


Currently in MapServer 3.5, WMS compliance has been completed so that
MapServer is capabable of responding to WMS requests.  Documentation for
use of WMS should be published shortly.

Under development is the ability for MapServer to "Cascade".  This is
the ability to call multiple servers through WMS and overlay resulting
maps to return a single image to the end-client.  Images are overlayed
by setting all pixels in each image where no data is found to
transparent so that layers beneath can be seen.  This will be completed
through the end of this summer.

I hope that helps clear up what to expect somewhat.  If I'm mistaken in
some of the technical details, please someone correct me.  Look for a
lot more information to be available concerning WMS in the coming weeks.

Dave


"Hockaday, John" wrote:
> 
> Hi Claudia,
> 
> I was hoping that someone with more experience with this type of subject
> would answer your question but it seems that they haven't so I will give you
> the little knowledge that I have on the subject.  Hopefully, lots of people
> will get annoyed with the errors in this e-mail that I am proposing and they
> will correct me for your benefit.  I for one am very interested in the
> outcomes of your project as I will have to look into something similar soon.
> 
> The Open GIS came up with a standard for accessing data across the web.  (I
> think that the OpenIGS is called something different now but I'm not sure.)
> One of the commands is something like getimage().  I believe that mapserver
> version 3.5 has the ability to handle Open GIS capabilities.  I seem to
> remember earlier versions having the getimage() command but I'm not sure
> about that either.
> 
> You could use the getimage() command to each of your mapservers and they
> should return an image.  You could then build these images on top of each
> other, if they are transparent, to make a final map.  GD can do this if
> mapserver doesn't already have a command to do it.  You may have to make
> more that one call to each map server as the order of the layers may be
> important to your final map.
> 
> I think that there is a similar OpenGIS command to get information about a
> layer from a remote map server.  It may be something like getinfo().  This
> is probably a more simpler command as it may only need information from one
> mapserver.
> 
> I would *strongly* recommend that you use the OpenGIS standard as a lot of
> work has gone into this standard and you will greatly benefit from their
> detailed efforts.  I worked on a system of connecting to many map producing
> servers a long time ago and it was full of problems therefore, we stopped
> doing it.  Since then, the OpenGIS has addressed those problems in their
> work.
> 
> Good luck and please keep this list aware of what you are doing.  I want to
> build on your work if you don't mind me "borrowing" your intellectual
> property and code.   ;--)
> 
> John
> 
> > -----Original Message-----
> > From: Claude Philipona [SMTP:claude.philipona at camptocamp.com]
> > Sent: Friday, July 13, 2001 8:38 PM
> > To:   mapserver-users at lists.gis.umn.edu
> > Subject:      [mapserver-users] mapserver architecture for multi-websites
> > on several machines
> >
> > We are starting a project using Mapserver (PHP/MapScript) for building a
> > cartographic server which could be used by different client web-sites on
> > different machines. The server will propose a large set of raster map from
> > 1:25'000 to 1:1'000'000. The client web-sites will be able to use the
> > central
> > mapserver to interactivly geocode any kind of information (points, lines,
> > surfaces) using an applet and to visualize and to navigate thru the
> > obtained
> > geocoded objects.
> >
> > Each site using Mapserver is totally independent should be able to
> > integrate the
> > map directly (no frames).In this configuration we don't have a web borwser
> > making
> > direct request to MapServer, but rather the web server machines would have
> > to
> > make the cartogrphic request to the mapserver machine. This is a kind of
> > wms.
> >
> > My question: What is the best solution to implement this kind of
> > architecture?
> > Has anybody already done such thing?
> >
> > My ideas were to use WDDX (Web Distributed Data Exchange,
> > http://www.openwddx.org/faq/) to exchange the required parameters between
> > the
> > mapserver box (coordinates of the click, shapes ON,...) and the webserver
> > boxes
> > (url of the map image,...). So the Webserver (php enabled) would post a
> > wddx file
> > (containing the serailzed parameter) to the MapServerPHP-MapScript. After
> > deserialization PHP/Mapscript will process the map request and return wddx
> > file
> > (containing the url of the images and other important parameter).
> >
> > Is it the way to go to get good performance? Is there a better way to do
> > it?
> >
> > Other question: I was palnning to start this development using directly
> > Mapserver
> > 3.5, providing that the system will not enter in production before
> > november. Is
> > 3.5 stable enough? Any timesacle for the official release?
> >
> > Claude Philipona

-- 
Dave McIlhagga
President, DM Solutions Group

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