[Qgis-developer] Quick fixes and error communication for ftools

Tue Nov 24 02:13:26 PST 2015

Hi Marco

On 11/24/2015 11:01 AM, Marco Hugentobler wrote:
> Hi Alessandro, Matthias
>
> >Is there no requirement for multi types?
>
> Afaik, the problem for f-tools are not the multi types, but only the
> geometry collections (containing geometries with different shape
> type). In my experience, if geos returns a geometry collection, it
> usually contains one 'expected' geometry and the others are slivers
> (@strk, please correct me if wrong).

I was mostly thinking about collections that contain a multitype with
several parts which are not considered slivers. This seems to be a very
valid scenario.

>
> >Based on what indicator should be chosen what to extract? Try
> polygons first, if there are none try lines, if there are none take
> points? 
>
> One possibility would be to pass the expected shapetype (Point / Line
> / Polygon) to the function and take the best candidate (e.g. longest
> line, largest polygon area).

Before the geometry changes, the algorithms were able to provide the
results without this additional information. How was that done?

>
> >How much effort (in time) do you think is required to implement this fix?
>
> Difficult to estimate. It seems straightforward to implement the
> extraction function. Then it needs to be called by the f-tools
> internally and be tested with a few examples. If unit tests are
> required (as mentioned by Alessandro), this seems to be the most time
> consuming task to me.
Unit Tests for processing are on my todo list anyway (I think as a psc
member you should have voted for that ;) )

Matthias
>
> Regards,
> Marco
>
> On 24.11.2015 10:42, Matthias Kuhn wrote:
>> Hi Marco
>>
>> Good to have your feedback, you probably know the problem best.
>>
>> On 11/24/2015 09:28 AM, Marco Hugentobler wrote:
>>> Hi
>>>
>>> >ad issue 1: update fTools to warn users when some features cause
>>> problems
>>> >ad issue 2: quick fix fTools to convert geometry collections to
>>> single geometry types
>>>
>>> A function that takes a geometry type and extracts the longest line
>>> / the largest polygon / the first point from the geometry collection
>>> should be straightforward to do.
>>
>> Is there no requirement for multi types?
>> Based on what indicator should be chosen what to extract? Try
>> polygons first, if there are none try lines, if there are none take
>> points?
>>
>>>
>>> >These fixes/updates would be made available as fTools updates via
>>> the plugin installer asap
>>>
>>> If the fix does not take too long, we probably don't need a warning
>>> at all.
>>
>> How much effort (in time) do you think is required to implement this fix?
>>
>> Regards,
>> Matthias
>>
>>>  
>>> Regards,
>>> Marco
>>>
>>> On 23.11.2015 21:35, Anita Graser wrote:
>>>> Hi,
>>>>
>>>> If you are following the psc list, you've probably seen the thread
>>>> discussing current shortcomings of ftools
>>>> (http://lists.osgeo.org/pipermail/qgis-psc/2015-November/003623.html)
>>>>
>>>> In short, the key issues are:
>>>> 1. When ftools encounter issues with certain features, warning
>>>> messages get written to the log but this is largely hidden from
>>>> users since they would actively have to actively monitor the log.
>>>> The problematic features are then missing from the results but this
>>>> is not always obvious. 
>>>> 2. The above issue is more common now (since 2.10) since underlying
>>>> libraries more often (and correctly so) produce geometry
>>>> collections as outputs. These geometry collections are not handled
>>>> well by the current ftools code which is much older.
>>>>
>>>> To address these issues, the following suggestions have been made
>>>> so far: 
>>>> ad issue 1: update fTools to warn users when some features cause
>>>> problems
>>>> ad issue 2: quick fix fTools to convert geometry collections to
>>>> single geometry types
>>>>
>>>> For the warnings, there's already a first PR
>>>> draft https://github.com/qgis/QGIS/pull/2432 which needs to be
>>>> fleshed out. 
>>>>
>>>> These fixes/updates would be made available as fTools updates via
>>>> the plugin installer asap. 
>>>>
>>>> If you have ideas how to handle this efficiently or have already
>>>> implemented code that addresses similar issues, let us know. 
>>>>
>>>> It would be good to have a quick discussion in order to be able to
>>>> provide improvements fast.
>>>>
>>>> Best wishes,
>>>> Anita
>>>>
>>>>
>>>> _______________________________________________
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>>>
>>>
>>> -- 
>>> Dr. Marco Hugentobler
>>> Sourcepole -  Linux & Open Source Solutions
>>> Weberstrasse 5, CH-8004 Zürich, Switzerland
>>> marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
>>> Technical Advisor QGIS Project Steering Committee 
>>>
>>>
>>> _______________________________________________
>>> Qgis-developer mailing list
>>> Qgis-developer at lists.osgeo.org
>>> List info: http://lists.osgeo.org/mailman/listinfo/qgis-developer
>>> Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-developer
>>
>> -- 
>> Matthias Kuhn
>> OPENGIS.ch - https://www.opengis.ch
>> Spatial • (Q)GIS • PostGIS • Open Source
>>
>>
>> _______________________________________________
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>> List info: http://lists.osgeo.org/mailman/listinfo/qgis-developer
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>
>
> -- 
> Dr. Marco Hugentobler
> Sourcepole -  Linux & Open Source Solutions
> Weberstrasse 5, CH-8004 Zürich, Switzerland
> marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
> Technical Advisor QGIS Project Steering Committee 
>
>
> _______________________________________________
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> List info: http://lists.osgeo.org/mailman/listinfo/qgis-developer
> Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-developer

-- 
Matthias Kuhn
OPENGIS.ch - https://www.opengis.ch
Spatial • (Q)GIS • PostGIS • Open Source

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