[Qgis-developer] WPS server

[rldhont]

Le 03/12/2012 14:05, Martin Dobias a écrit :
> Hi Rene-Luc
>
> On Mon, Dec 3, 2012 at 10:01 AM, rldhont <rldhont at gmail.com 
> <mailto:rldhont at gmail.com>> wrote:
>
>     With the QGIS Expression you just have to know how to write an
>     expression to create a new Process. It's not coding.
>     For example the Buffer Process can be described like this :
>     buffer("geometry","distance")
>     You want to create a Process which retrun the buffer without the
>     geometry :
>     difference(buffer("geometry","distance"),"geometry")
>     And we can define a Process which return the result of a QGIS
>     Expression as the Process parameter.
>
>
> Thanks for sharing your thoughts about your implementation.
>
> I would like to express my concerns that using QgsExpression may be a 
> dead end for a generic WPS servers. Expressions are meant to deal with 
> individual features of a vector layer. You're right that it's possible 
> to define your own functions and chain them to create processes, but 
> this is very limited. For example it's not possible for a process to 
> return more results and it's not possible to use one result more than 
> once. Just like raster calculator has its own expression engine, also 
> the processing service should use a way of describing algorithms that 
> suits best its needs - and in our case that's python+SEXTANTE.
>
> Therefore I strongly recommend using SEXTANTE for the WPS server 
> backend. I believe that would be less work than trying to hack 
> QgsExpression to use it for processing. You would just need to parse 
> WPS query, generate a Python script that would run SEXTANTE analysis 
> and then create WPS reply. It's probably not desirable to run the 
> processing directly within the server process (thread), so this would 
> be a better solution either way.

Hi Martin,

My idea was to have a simple WPS server based on QGIS-Server, very 
simple for simple vector case, and I thought it's a good idea. I only 
need to validate geometry, constructing simple buffer or intersection.

For big processing, I think SEXTANTE is better suitable, but for a WPS 
serveur, SEXTANTE didn't need QGIS. We can construct a WPS Server based 
on pySextante with pyWPS.

I don't really want to hack QgsExpression, just accesses to very simple 
processing, I'll just it. For SEXTANTE, It will be better to work on 
someting based on pyWPS.

René-Luc


> Regards
> Martin

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