[Qgis-developer] Raster algebra C++

[Martin Dobias]

Hi Marco

On Thu, Oct 14, 2010 at 5:40 PM, Marco Hugentobler
<marco.hugentobler at sourcepole.ch> wrote:
> Hi devs,
>
> A very cool and handy tool is Alexander Bruys raster algebra plugin. It's so
> usefull in environmental modelling that Tim and I thought it would be good to
> have it in our analysis library (where it can be used by 3rd party
> applications too and without the dependency of the numpy library).
> So here is my initial patch that implements a calculator tool as part of the
> analysis library by extending the search string mechanism.
>
> [...]
>
> You can try the functionality by applying the following patch:
> http://karlinapp.ethz.ch/101014_qgis_rastercalculator.diff
> The menu to open the calculator is located under 'Layer->Raster calculator'.

Thanks a lot for the patch. I have taken a brief look on it and I have
one suggestion: IMHO it would be better to keep the parser (and
interpreter) for raster algebra and "search strings" separate. I
understand that it is easier to reuse some of the code from search
strings with raster algebra, but the semantics is very different. And
there are various functions and operators that work only for one of
them, so mixing them together complicates the inner working of the
search string interpreter. Extending the languages (e.g. usage of
raster neighborhood, further string operations) will make the code
even more cluttered.

My vision is that search strings should continue to evolve to support
a reasonable subset of SQL language, while raster algebra language can
evolve to support further raster/matrix operations. Keeping these
different languages separately may bring brighter future for both :-)

Regards
Martin