[Qgis-developer] Best practice for a new Vector Data Provider

[Jürgen E. Fischer]

Hi Sverre,

On Wed, 28. Jan 2015 at 12:05:25 +0000, Sverre Jonassen wrote:
> I am currently trying to make a new vector data provider with a source select
> dialog for QGIS so that QGIS can read and display data stored in a custom
> format. The format in question proprietary to software developed and
> maintained by the company I work at. I am quite new to developing for QGIS
> and I am struggling to find the best approach to do this. I hope that
> somebody out there can help me. I have not been able to find any internet
> resources on best practices for a data provider plugin.

UTSL.  You can browse through all provider in QGIS and look for one that is
close to what you need.


> So far, I have succeeded in creating a very simple vector data provider
> plugin and accessing it through a source select dialog (which I have added to
> the src/ui/-folder). This is, of course, not a suitable approach as it would
> mean that I have to build and deploy my own version of QGIS instead of a
> plugin. As far as I have understood it, there might be 3 possible approaches
> for me to make a new provider with a source select dialog:

> 1) An ordinary C++ plugin for the source select dialog containing the
>    provider. Is this possible? I have tried this and so far not succeeded.

I don't think that will work.  QGIS divides plugins into "ordinary" plugins and
providers.

 
> 2) A provider plugin containing all necessary ui. Is this possible? And
>    if so, how can I add a menu-item to activate the source select dialog?

That's the approach most providers (meanwhile) take.  You can export an entry
point "registerGui" that will be invoked with the application as argument.
With that pointer to you can lookup UI elements in the applicat0on and create
an insert new items you create.   Core providers usually don't use
this and there UI is hardwired in the application - some using the
"selectWidget" entry point.


> 3) A provider plugin without ui and a separate plugin with the source
>    select dialog.

That used to be the normal approach, when providers weren't supposed to link
the gui library.  As that changed I'd go for 2).


> A fourth option would be to create a plugin for OGR. This is, however, not a
> good solution for me because I would run a high risk of data conversion
> errors. Our format is much more similar to the QGIS internal geodata model
> than to the OGR geodata model.

Are you aware that you have to put QGIS providers and plugins under GPL?  That
means you have to make source code available to anyone you ship binaries to.

That doesn't apply to GDAL/OGR drivers.


Jürgen


-- 
Jürgen E. Fischer           norBIT GmbH             Tel. +49-4931-918175-31
Dipl.-Inf. (FH)             Rheinstraße 13          Fax. +49-4931-918175-50
Software Engineer           D-26506 Norden             http://www.norbit.de
QGIS release manager (PSC)  Germany                    IRC: jef on FreeNode                         
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