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

Tue Nov 24 02:29:05 PST 2015

On 24.11.2015 11:13, Matthias Kuhn wrote:
> 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.

It is, but it was also not handled by f-tools <= 2.8.

>
>>
>> >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?

Not sure. Maybe the logic in the geos -> QgsGeometry conversion handled 
the collections differently.

Regards,
Marco

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

-- 
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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