[Qgis-developer] Re: Qgis Raster Calculator

[Peter Ersts]

Howdy Tom.

I agree with most of what Tim has already said. I have been sadly unable 
to contribute much time to QGIS in the last couple of years. We had 
always talked about having these type of capabilities in the core raster 
classes but never moved forward for a couple of reasons other than just 
lack of time. One of reason was the raster class was so tightly wrapped 
around GDAL - perfectly fine approach -- but there was also always 
discussions of moving toward raster providers. So rather than invest 
loads of time yet more tightly couple features they were tabled ( or 
pushed to plugins ) until providers came online. Luckily Radim Blazek 
has stepped up recently and started to move raster providers close to 
reality.

This is a good time to start talking about these types of analysis 
capabilities because the raster providers will have to all be able to 
efficiently provide data in blocks for things like convolution masks and 
such. Hopefully Radim can comment a little on the status of the 
providers and how raw data will be made available to things like plugins 
and other core classes.

-pete

On 12/05/2010 05:00 PM, Tim Sutton wrote:
> Hi
>
> Note: Tom its better etiquette to write these kind of messages on the
> dev mailing list rather than mailing us directly. I'm replying to this
> via the developer mailing list and it would be great if you could
> continue the discussion there.
>
>
> On Sun, Dec 5, 2010 at 5:59 PM, Tom Holderness
> <tom.holderness at newcastle.ac.uk>  wrote:
>> Dear Peter,
>>
>> I'm e-mailing regarding the recent addition of the Raster calculator to Qgis 1.6.0 (and I've copied in a few others who may be interested).
>>
>> I am a third year PhD student, with a bachelors in Geographic Information Science, using long time-series Earth observation data for urban climate analysis. As part of my project (and as nothing suitable was available at the time) I wrote a basic Python library "PyRaster" based on GDAL for scripting of raster analysis routines (based on Numpy matrices), over large datasets (1000's of scenes). Other people in the research group are now using this for their own analysis, and recently I wrote a GUI in the form of a Qgis plugin the "raster processing suite" to make the library functions more accessible to non-technical users. The plugin includes a raster calculator and a recently added Python interface so that users can develop more advanced models (image processing code is generated on-the-fly from the GUI and presented to the user). This was my first Qt project so there are still a few things to improve before relasing v1.0 (current: 0.9.3).
>>
>> To save duplication of effort I wonder if my plugin and the Qgis raster calculator could be brought together to develop an in-built Qgis raster calculator within advanced processing capabilities.
>>
> I downloaded and tested your plugin using the link you provided below.
> On the face of it I can't see any functionality it has that isnt in
> the QGIS core raster calculator (but I only took a brief look), with
> the exception of your python code generator - which is indeed an
> interesting concept.
>
> The QGIS raster calculator is written in C++ and includes some
> features for dealing with rasters with different cell sizes etc, and
> it has been included in the newish qgis_analysis libarary with an eye
> to creating python bindings for it over time. It also has some
> features that yours misses I think like the ability to create boolean
> products using syntax lie raster at 1<  100.
>
>
>
>> I'm a big supporter of open-source geo projects (both my plugin and library are released under a BSD style license). There are obviously some technical "gaps" between the two projects, not least the difference between Python and C++ (I'm was a originally a C programmer), however, I would love to contribute to Qgis if possible.
> Marco did the work on contract to me for a project and programmed it
> in C++ for best speed and to get around the numpy in-memory aproach of
> previous raster calculator efforts. It would be great if you were
> interested to work directly on that. There are many features I would
> like to see in the calculator which it currently lacks. If you were
> interested in extending QGIS Raster Calculator I would be happy to
> discuss some of the features it misses. We always encourage those who
> wish to collaborate so if you have ideas, patches etc. just discuss
> them on the mailing list / submit patches via trac etc. - your inputs
> will certainly be appreciated.
>
>
>> The plugin is available within my repository:
>> www.students.ncl.ac.uk/tom.holderness/pyraster/qgis_repo.xml
>> More information can be found at:
>> www.students.ncl.ac.uk/tom.holderness/pyraster
>>
> Nice to see you are doing cool things with QGIS!
>
> Regards
>
> Tim
>
>> Kind Regards,
>>
>> Tom
>>
>> ----------------------------------------------------
>> Tomas du Chemin Holderness
>> Postgraduate Researcher
>>
>> School of Civil Engineering and Geosciences
>> Newcastle University
>>
>> Direct line:  +44 (0)191 222 6544
>> Web: www.students.ncl.ac.uk/tom.holderness
>>
>
>


-- 
====================================
Peter J. Ersts, Software Developer
American Museum of Natural History
Center for Biodiversity and Conservation
Central Park West at 79th Street
New York, New York 10024
Web: http://biodiversityinformatics.amnh.org
Web: http://cbc.amnh.org

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Quantum GIS Raster Development Team.