[Qgis-developer] Discussion: could Ice be used in Qgis ?

[Julien Michel]

Le 24/07/2015 10:31, Matthias Kuhn a écrit :
> Thank you for the hints. Please allow me one question here. I have
> recently plaied with OpenGL for rendering and did let the GPU do CRS
> transformation. I could not get it to work to my full satisfaction,
> based on the fact that I only had float but no double precision.
> Therefore e.g. CRS 21781 (in meters) already uses 6 figures for
> meters, one more is still ok but when you zoom into cm resolution you
> start to see the precision / rounding errors in rendering.
> For reprojection I guess you had to also deal with precision of
> coordinates. Did you use OpenGL features which are able to use double,
> transform coordinates into an intermediate format before sending them
> to the GPU or something totally different?

Hi Matthias,

Sorry for the late reply. For now Ice does not do anything specific to 
prevent loss of precision of coordinates in rendering, so this is 
another stone in Ice garden. However, I think that a fairly simple 
workaround is to shift/scale coordinates before rendering (for instance 
according to the data bouding box), eventually even change shift/scale 
settings with respect to zoom level, so that to ensure a controlled 
precision of coordinates in rendering. An example of software doing this 
is CloudCompare, which is a very good points clouds visualization 
software. If you load a point cloud with large coordinates, it will warn 
you about possible precision loss and propose to shift/scale the 
coordinates.

Hope that helps,

Regards,

Julien

-- 
Julien MICHEL
CNES - DCT/SI/AP