[gdal-dev] Layer operations, a proposal

[Ari Jolma]

On 04/18/2012 03:07 AM, Jason Roberts wrote:
> As I have mentioned previously
> (http://lists.osgeo.org/pipermail/gdal-dev/2010-January/023089.html)

Thanks for pointing this out.

>   I think
> something like this would be a great addition to OGR. No doubt it would be a
> huge job--basically turning OGR into a GIS--but if it could be done well,
> with sufficient performance and in the core API, then many systems could
> potentially leverage it, instead of everybody implementing their own
> versions of Ari's pseudocode.

I don't think it would be a huge job. Maybe I'm missing something but I 
see the basic implementation very simple and generic. Perhaps there is a 
performance problem somewhere (looping through 1 million features within 
a loop of 1 million features and using shapefiles) but for common cases 
it should be ok, especially if the layers fit into memory.

Once I get something done (currently testing the 2nd algorithm), it 
would be interesting to do some benchmarking with available datasets.

Best regards,

Ari

>
> Best,
> Jason
>
> -----Original Message-----
> From: gdal-dev-bounces at lists.osgeo.org
> [mailto:gdal-dev-bounces at lists.osgeo.org] On Behalf Of Frank Warmerdam
> Sent: Tuesday, April 17, 2012 7:32 PM
> To: Ari Jolma
> Cc: gdal-dev at lists.osgeo.org
> Subject: Re: [gdal-dev] Layer operations, a proposal
>
> Ari,
>
> I think this would be an interesting addition.   Would you be willing
> to write up an RFC?
>
> I think the layer creation step should be a different call than the feature
> processing step to maximize the chance that folks who need to do something
> very format specific at layer creation can do so and still use the generic
> algorithm for processing the features.
>
> Your operations appear to be focused on spatial relationships, but I've also
> heard a lot of interest in feature joins on attribute fields.  One case is
> just merging features from a layer with a common attribute value.  Another
> case would be some sort of attribute based join between layers.  Hopefully
> we can use a reasonably similar approach for a variety of operations.
>
> I'm curious how you plan to handle the spatial relationships efficiently?
> An in memory spatial index?  I'd like have the API overly constrain how we
> implement this as I can imagine the internal operation implementation
> evolving over time, and perhaps taking different strategies for different
> styles of input data.  For instance an in-memory spatial index might not
> make much sense for large numbers of very simple point features while it
> would be good for heavy polygon features.
>
>
> Best regards,
> Frank
>
> On Tue, Apr 17, 2012 at 2:42 PM, Ari Jolma<ari.jolma at gmail.com>  wrote:
>> Folks,
>>
>> I propose a set of new methods for OGR layers (see the PDF). I took
>> the basic ideas from page
>> http://courses.washington.edu/gis250/lessons/Model_Builder/ which
>> seems rather comprehensive. I wrote the pseudo code myself quickly
>> (thus it may not be optimal and may contain bugs - improvement
>> suggestions are of course welcome).
>>
>> I was considering to write these in Perl (on top of the Perl bindings)
>> but probably they could also be in OGR core. Code-wise they would
>> probably go into ogrlayer.cpp.
>>
>> If there is support/interest, I assume I should submit this as a RFC
>> (with a patch)?
>>
>> Best regards,
>>
>> Ari
>>
>>
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>
>