[Qgis-developer] How to change layer without redrawing the whole map

[Marco Hugentobler]

Hi Jonny

One possibility to handle this is to create a subclass of 
QgsMapCanvasItem to display the car symbols. That way, the QGIS 
background map is not re-rendered if the items change position.

Regards,
Marco

On 02.11.2011 09:26, Kanwar, Jonny wrote:
> Dear all,
>
> We would like to write a Qgis plugin (either C++ or python, doesn't
> matter) that allows us to visualize movements of vehicles over time.
> Suppose the plugin provides coordinates for each second and vehicle. Our
> fear is that for each frame to be rendered the whole map is redrawn. Do
> you see a way to enable Qgis to only update the animated layer and not
> all layers at once?
>
> We know there is the time manager plugin that provides capabilities
> similar to our requests. However, at our tests, this plugin suffered of
> poor performance.
>
> To get a bit more technical: As far as I understand the QgsMapCanvas has
> to be redrawn as soon as a single element of one of the layers changes.
> Is there a way to add some overlay that is just merged with the other
> (already rendered) image?
>
> Thanks for your support.
>
> Jonny Kanwar
>
>
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