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

Tue Nov 24 15:00:28 PST 2015

May be tested against test dataset provided by werner macho and Giovanni
Manghi?

On Tuesday, 24 November 2015, Matthias Kuhn <matthias at opengis.ch> wrote:

> Thank you Marco,
>
> Are you confident that these are the only places that need changes, so
> does this mean that there is no more reason for a warning and we just need
> a quick point release?
> I applied the same to processing and did some changes to your fix to make
> it work also for union and clip.
>
> Regards
> Matthias
>
> On 11/24/2015 04:58 PM, Neumann, Andreas wrote:
>
> Thank you Marco! Much appreciated.
>
> Andreas
>
> On 2015-11-24 16:36, Marco Hugentobler wrote:
>
> Hi all
>
> I had a detailed look with the debugger at what happens in the different
> versions. It turned out fTools does indeed handle geometry collections, but
> assumed a geometry collection has wkb type 'unknown' (which was true <=
> 2.8, but now geometry collections are not unknown anymore). Commit
> <https://github.com/qgis/QGIS/commit/594fafe73b80d91d94b962c2e51aea0b0168a08a>
> https://github.com/qgis/QGIS/commit/594fafe73b80d91d94b962c2e51aea0b0168a08a
> should solve the issue and bring back the old behaviour.
>
> Regards,
> Marco
>
>
>
> On 24.11.2015 11:29, Marco Hugentobler wrote:
>
> 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>
> 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>
> 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, Switzerlandmarco.hugentobler at sourcepole.ch <javascript:_e(%7B%7D,'cvml','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
>
>
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>
> --
> Dr. Marco Hugentobler
> Sourcepole -  Linux & Open Source Solutions
> Weberstrasse 5, CH-8004 Zürich, Switzerlandmarco.hugentobler at sourcepole.ch <javascript:_e(%7B%7D,'cvml','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
>
>
>
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>
>
> --
> Dr. Marco Hugentobler
> Sourcepole -  Linux & Open Source Solutions
> Weberstrasse 5, CH-8004 Zürich, Switzerlandmarco.hugentobler at sourcepole.ch <javascript:_e(%7B%7D,'cvml','marco.hugentobler at sourcepole.ch');> http://www.sourcepole.ch
> Technical Advisor QGIS Project Steering Committee
>
>
>
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>
>
> --
> Dr. Marco Hugentobler
> Sourcepole -  Linux & Open Source Solutions
> Weberstrasse 5, CH-8004 Zürich, Switzerlandmarco.hugentobler at sourcepole.ch <javascript:_e(%7B%7D,'cvml','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
>
>

-- 
Luigi Pirelli

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