[Geoserver-devel] Lowering entry barriers a little more

GeoServer GeoServer Developer
1

Hi guys,
a user on IRC today asked for brief explanation of
WMS/WFS/WCS and well, I had none. Do you know of
any online article we could link for brief explainations
on the respective protocols.

You know, it would not be bad if Geoserver became something
that a user can simply use to publish maps or integrate
with Google Earth/Map/Whatever, without the need to be
exposed with the protocol crazyness :slight_smile:

Cheers
Andrea

2

I usually describe it as ...
Web Map Server - displays Maps ready to use in something like OpenLayers or uDig, has support for KML so it can show up in google earth
Web Feature Server and Web Coverage Server - actually access to the data (rather than just a picture of it) in case you want to do something crazy

Cheers,
Jody

Hi guys,
a user on IRC today asked for brief explanation of
WMS/WFS/WCS and well, I had none. Do you know of
any online article we could link for brief explainations
on the respective protocols.

You know, it would not be bad if Geoserver became something
that a user can simply use to publish maps or integrate
with Google Earth/Map/Whatever, without the need to be
exposed with the protocol crazyness :slight_smile:

Cheers
Andrea

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3

Jody Garnett ha scritto:

I usually describe it as ...
Web Map Server - displays Maps ready to use in something like OpenLayers or uDig, has support for KML so it can show up in google earth
Web Feature Server and Web Coverage Server - actually access to the data (rather than just a picture of it) in case you want to do something crazy

Yeah, me too, ha ha ha ha :slight_smile:
Ok, seriously, I guess that user wanted a middle ground between
the one line description and the hundreds technical pages you
get in the OGC specs :slight_smile:

Cheers
Andrea

4

I'd start with a "Design By Contract" look at the issue.

WMS - the contract is that the server promises to understand the spatial context and image (size, format, transparency) parameters the client wants in a map
The client will use the layers discovered (directly or indirectly) from the GetCapabilities call, preferably within the hints.

WFS, the contract is to deliver some (capped) number of features in response to a filter, using a FeatureType the client understands - i.e. encoded in the format requested, where the "normative" format is GML, and other potentially lossy formats may be used if the client thinks they can interpret the potentially munged content.
Again, the client should respect the FeatureTypes listed in the getCapabilities response, but in reality needs to know far more about the content to be able to formulate a sensible query. WFS only makes sense within the context of an external set of contracts describing the objects.

(We often assume this contract to be somethign like..... "I hope you will deliver a set of features within this bounding box that are simple enough for me to find the same type of geometry property for each Feature, and are not too many to kill the network connection or my ability to parse, or at least I will try to interpret a small subset indistinguishable from the actual potential result set, and I probably wont try to make any other interesting filters because I wont know the content until I've got it all.....".
This is why I personally believe that suport for well-known FeatureTypes and content standards will be necessary ultimately, just to simplify the nature of the contract between server instances and clients.)

WCS is a stranger beast by far, semantically, because it applies a subsetting operation to a Feature (subtype Coverage) to deliver a related Feature encoded as a range+domain (i.e. coverage). Best to think of it as a raster data subsetting convenience operation delivered through a standardised protocol IMHO.

RA

Andrea Aime wrote:

Jody Garnett ha scritto:
  

I usually describe it as ...
Web Map Server - displays Maps ready to use in something like OpenLayers or uDig, has support for KML so it can show up in google earth
Web Feature Server and Web Coverage Server - actually access to the data (rather than just a picture of it) in case you want to do something crazy
    
Yeah, me too, ha ha ha ha :slight_smile:
Ok, seriously, I guess that user wanted a middle ground between
the one line description and the hundreds technical pages you
get in the OGC specs :slight_smile:

Cheers
Andrea

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5

Here are some of the resources we've developed to answer just these questions:

WMS: http://lyceum.massgis.state.ma.us/wiki/doku.php?id=wms:home

WFS: (we link to this great one on the UDIG site) http://udig.refractions.net/confluence/display/GOWS/WFS

--saul

________________________________

From: geoserver-devel-bounces@lists.sourceforge.net on behalf of Andrea Aime
Sent: Mon 5/28/2007 1:38 PM
To: Geoserver-devel
Subject: [Geoserver-devel] Lowering entry barriers a little more

Hi guys,
a user on IRC today asked for brief explanation of
WMS/WFS/WCS and well, I had none. Do you know of
any online article we could link for brief explainations
on the respective protocols.

You know, it would not be bad if Geoserver became something
that a user can simply use to publish maps or integrate
with Google Earth/Map/Whatever, without the need to be
exposed with the protocol crazyness :slight_smile:

Cheers
Andrea

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Download DB2 Express C - the FREE version of DB2 express and take
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6

Farber, Saul (EEA) ha scritto:

Here are some of the resources we've developed to answer just these questions:
WMS: http://lyceum.massgis.state.ma.us/wiki/doku.php?id=wms:home
WFS: (we link to this great one on the UDIG site) http://udig.refractions.net/confluence/display/GOWS/WFS

Woot, nice ones Saul.
Ok, I set up a page with those two and Ian Turton course, if people
have more, I'll gladly add them.

http://docs.codehaus.org/display/GEOSDOC/More+documentation+on+OGC+services

Cheers
Andrea