[Qgis-developer] On the fly simplication of point layers

[Tim Sutton]

Hi


On Fri, Jan 24, 2014 at 1:12 AM, A Huarte <ahuarte47 at yahoo.es> wrote:

> Hi!
>
> About simplification (no clustering), I think that the If we discard
> points based on the distance to the last fetched and rendered point (
> https://github.com/qgis/QGIS/blob/master/src/core/qgsfeatureiterator.cpp#L36)
> it will be very effective to render big dense points layers. I have a GIS
> application using this technique and it draws LAS files (> 30mb) "fast".
>
> I would like write a "point simplifier" in QGIS to validate results.
> Do you agree ?
>

I think this would be great. Since you are doing a full scan of the
dataset, you should be able to count how many points each aggregate point
represents right? I was thinking we could pass that the the renderer as a
'virtual' attribute so that we can use it to e.g. scale the symbol size.

+1 from me to implement this anyway as a new cluster renderer (or a patch
the point displacement renderer if that seems workable).

Regards

Tim


>
> Alvaro
>
>   ------------------------------
>  *De:* Tim Sutton <lists at linfiniti.com>
> *Para:* Martin Dobias <wonder.sk at gmail.com>
> *CC:* qgis-developer <qgis-developer at lists.osgeo.org>; "
> tech at wildintellect.com" <tech at wildintellect.com>
> *Enviado:* Jueves 23 de enero de 2014 23:16
>
> *Asunto:* Re: [Qgis-developer] On the fly simplication of point layers
>
> Hi
>
>
> On Wed, Jan 22, 2014 at 2:47 PM, Tim Sutton <lists at linfiniti.com> wrote:
>
> Hi
>
>
> On Wed, Jan 22, 2014 at 1:23 PM, Martin Dobias <wonder.sk at gmail.com>wrote:
>
> On Wed, Jan 22, 2014 at 4:33 PM, Tim Sutton <lists at linfiniti.com> wrote:
> >>
> >> Actually the point displacement renderer already does clustering,
> >> though it lacks more options to customize how the clustered symbol
> >> would look like.
> >>
> >
> > Doesnt it do the reverse? i.e. when more than one point falls in the same
> > place, it shifts them aside so they are all visible. If it can be made to
> > produce a scaled symbol based on the number of underlying points that
> would
> > be cool.That would also be a good time to change its name to 'Custer or
> > displace' or something.
>
> I think that was what the renderer did originally, but nowadays it
> also groups points within configured distance. Unfortunately it always
> tries to draw a circle around the clustered point with original
> symbols. If we introduced few rendering options, it would be more
> useful:
> - draw just the clustered symbol for the whole group
> - scale the clustered symbol depending on the number of points inside
>
>
> Yeah that should do it!
>
>
> I tested with a large point dataset (geonames ~3.5 million records).
> Basically enabling the point displacement renderer on that layer kills (or
> takes so long I killed it) QGIS. Since the essence of clustering is to
> speed up rendering times and reduce visual clutter, I suspect simple tweaks
> to the renderer would not be enough.
>
> Regards
>
> Tim
>
>
>
>  Regards
>
> Tim
>
>
> Cheers
> Martin
>
>
>
>
> --
> Tim Sutton - QGIS Project Steering Committee Member
> ==============================================
> Please do not email me off-list with technical
> support questions. Using the lists will gain
> more exposure for your issues and the knowledge
> surrounding your issue will be shared with all.
>
> Irc: timlinux on #qgis at freenode.net
>
> ==============================================
>
>
>
>
> --
> Tim Sutton - QGIS Project Steering Committee Member
> ==============================================
> Please do not email me off-list with technical
> support questions. Using the lists will gain
> more exposure for your issues and the knowledge
> surrounding your issue will be shared with all.
>
> Irc: timlinux on #qgis at freenode.net
> ==============================================
>
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>
>


-- 
Tim Sutton - QGIS Project Steering Committee Member
==============================================
Please do not email me off-list with technical
support questions. Using the lists will gain
more exposure for your issues and the knowledge
surrounding your issue will be shared with all.

Irc: timlinux on #qgis at freenode.net
==============================================
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