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

Martin Dobias wonder.sk at gmail.com
Fri Jan 24 01:21:02 PST 2014

Hi Andreas

On Fri, Jan 24, 2014 at 3:48 PM, Andreas Neumann <a.neumann at carto.net> wrote:
> Hi Martin,
> So you think the same code of the point displacement renderer can also
> be used for clustering?
> It was developed exactly for the opposite: if multiple geometries are on
> top of each other they are displaced so you can see all of the points. A
> use-case is where several people live at the same address but have
> different attributes and you want to see them all.
> I am a bit surprised that the same code could be used for the opposite -
> to cluster points that are not at the same position. Wouldn't it require
> some additional code/work to do that?

When looking into the code history, there always used to be support
for a tolerance when two points are considered to be at the same
place. So the renderer always did grouping of nearby points, although
it was not originally designed to handle lots of points. And if we
display just the "group" symbol (without individual grouped markers),
there is the clustered marker renderer, isn't it? :-)

>From the technical point of view it is the same thing and the
difference is I think mainly in the use: point displacement is meant
for few close points (e.g. within a distance of 5 meters), while
marker cluster would be used for lots of points (and the distance is
best entered in pixels rather than map units to keep the map readable
with any scale).


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