[GRASS-dev] v.external, ogr direct access, topology and pseudo-topology.... a bit confused

[G. Allegri]

The language doesn't help, so please forgive me if I haven't been clear: I
don't expect from grass something more or something less, I was wondering if
with the new grass 7 features (like direct ogr access) it was possible to
make some daily operations faster.

I frequently use SAGA for spatial processing, so I have its features in
mind... So I just was looking how to unify the various needs (more or less
rigorous) in a single environent, like grass.

giovanni

2010/4/19 Moritz Lennert <mlennert at club.worldonline.be>

> Jumping into the debate, since it raises some fundamental questions in my
> eyes;
>
>
> On 19/04/10 17:46, G. Allegri wrote:
>
>> No problem, this is not what I expect. I just expect a user to be able
>> to import a polygonal layer, without worrying about topology correctness
>> (clean/build operations), and do spatial operations on it. Obviously the
>> correctness of results depend on the operation the user is doing (and
>> it's his problem) but, i.e. a geometrical clip will be always correct, I
>> think...
>>
>
> The questions here for me are:
>
>
> - What is the actual error linked to doing operations on non-topological
> formats ?
>
> - Why do you absolutely want GRASS to do this ? If all you want to do is
> simple geometry operations on spaghetti files, you can easily do this with
> most of the available open source viewers / GIS, such as QGIS, gvSIG, uDIG,
> etc or even directly with ogr. Why go through the trouble of using GRASS for
> that ?
>
>
>  These operations should be quite fast for native vectors with topology.
>>>
>>
>> With "rapidly" I meant: load data, do-the-op, save the results. I'm sure
>> that the native grass data structures can deal more efficiently then SF
>> structures.... but often a user prefer to wait a minute more for the
>> operation to end, then working a minute to have to manage the data
>> cleaness (more often it takes much more then a minute, and it doesn't
>> worth it!)
>>
>>  > Yes, although not that rapidly because pseudo-topology needs to be
>> built first. Polygons do not need to be clean, but then nobody can
>> guarantee for the results.
>>
>> Ok, but the user just have to wait and wath the progress bar
>> completing... that's ok from his perspective :)
>>
>
> I find it a bit suspicious when user comfort is apparently put so much
> higher in priority then correctness of results...
>
> Moritz
>
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