[gdal-dev] calculate raster values within a vector

[Emilio Mayorga]

n Wed, Aug 26, 2009 at 9:37 AM, Jose Gomez-Dans<jgomezdans at gmail.com> wrote:
> 2009/8/26 Dylan Beaudette <debeaudette at ucdavis.edu>
>>
>> ndeed. The current (C++) version of Starspan is more or less unsupported.
>> I tend to use an older, stabler, version-- but have become frustrated with
>> it in recent studies. I think that the current maintainer Jon Greenberg is
>> working on an R implementation-- however I am not certain that this will
>> scale well to very large rasters. A Python incantation would be more
>> flexible
>> than the current C++ version, but perhaps at a speed cost. The current
>> version is blazing fast, but there aren't any C++ programmers working on
>> it now. If there is sufficient interest, I would like to get it into OSGeo so
>> that a more skilled programmer (than myself) can have a look at it.
>
> Python is extremely fast for some of these things. The version I tend to use
> < http://sites.google.com/site/spatialpython/zonal-statistics> is bearable
> even working with whole landsat scenes. The example there (with one MODIS
> 1km tile) takes in my laptop:
> %timeit S = ZonalStats ( labels_file, data_file, stats='mean') ; std_s =
> S.ResampleToGrid("std")
> 10 loops, best of 3: 1.44 s per loop
>
> %timeit S = ZonalStats ( labels_file, data_file, stats='mean') ; std_s =
> S.ZonalStatistics("mean")
> 10 loops, best of 3: 359 ms per loop
>
>
> I plan to add a number of refinements to the code, such as adding a vector
> input that gets automaticall rasterised, something that the GDAL python
> wrappers have allowed for quite some time now, and adding these values to
> the output as extra fields, but so far, I have had no need for these, so I
> haven't really bothered.

Wow, Jose, thanks for sharing that! It looks terrific. I may be able
to contribute to it, but not until October or so.


> 2009/8/26 Dylan Beaudette <debeaudette at ucdavis.edu>
> If you are doing raster-on-raster zonal stats, then GRASS is fairly good at
> that too.

Dylan, thanks for your comments on Starspan. Regarding GRASS, I wish I
had time to start using it, but so far I haven't been able to. One of
these days... Still, accessing this functionality from Python is a big
plus for me. For example, I'm sharing some of my zonalstats-like code
with a colleague. I've helped him set up Python with all the right
modules, and he can run my code. Adding GRASS to that bag of new
things would probably make this task too complicated. Anyways, that's
just my own preferred workflow. I'll get to GRASS one of these days...

Cheers,

-Emilio