[Qgis-developer] Lidar data into QGIS

A Huarte ahuarte47 at yahoo.es
Wed Jan 29 06:19:52 PST 2014

You are right, but only if it is possible to generate the quadtree on the fly (millions of points), or preprocess it to disk.

this doc uses a mixed strategy (I used it and it works fine)...

a first pass read the file to build a special quadtree which only save the number of points of each quad-item.
when the data is readed, it accumulates the points, and when a quad-item has all points, then it returns a releases the buffer of this quad-item.


> De: Jean-Roc Morreale <jr.morreale at enoreth.net>
>Para: A Huarte <ahuarte47 at yahoo.es> 
>CC: qgis-developer at lists.osgeo.org 
>Enviado: Miércoles 29 de enero de 2014 14:25
>Asunto: Re: [Qgis-developer] Lidar data into QGIS
>Most lidar files are not spatially ordered so with a sequential read you 
>will end up reading the whole file, it's like accessing a untiled 
>unpyramided bigtiff : painful.
>Le 2014-01-29 13:52, A Huarte a écrit :
>> I think but using a quadtree approach there is a problem, and it is
>> none other than the construction of the quadtree itself for so big
>> data.
>> IMHO I would use a specific provider (with a specific featureiterator)
>> reading sequentially the LAS file and discarding points before fetch
>> it to renderer using the RectangleFilter of current FeatureRequest. It
>> avoid create many-many QgsFeature's that after are discarded in
>> renderer side.
>> I use this technique in a personal viewer, and after first read of
>> file (the file is cached in SO), the following drawings are quite
>> fast.
>> Alvaro
>>> -------------------------
>>> DE: Jean-Roc Morreale <jr.morreale at enoreth.net>
>>> PARA: qgis-developer at lists.osgeo.org
>>> ENVIADO: Miércoles 29 de enero de 2014 13:32
>>> ASUNTO: Re: [Qgis-developer] Lidar data into QGIS
>>> Can it performs fast enough to display hundred millions points or
>>> billions at once ? Does it leverage a quadtree approach ?
>>> Le 2014-01-29 12:55, A Huarte a écrit :
>>>> yes, it can be implemented on renderer level (Martin Dobias
>>> propose
>>>> it) or on featureiterator level similar to current simplification
>>>> classes for line and polygons
>>>> I think it is pending for a test of performance
>>>> Best Regards
>>>> Alvaro
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