[vtkusers] UTM coordinates, double precision, structured and unstructured grids

David E DeMarle dave.demarle at kitware.com
Wed Jul 11 19:34:56 EDT 2012


This is opengl precision. The solutions I've seen subtract to single
precision as you've done. Newer cards, or alternatively specially
configured mesa, are potential alternatives.
On Jul 11, 2012 6:50 PM, "Richard R McDonald" <rmcd at usgs.gov> wrote:

> Hello,
>
> We have an application that provides pre- and post- processing
> capabilities for computational models of flow and sediment transport in
> Rivers.  The application is built with Qt and VTK.  We use both structured
> and unstructured grids.  The grid x,y locations, stored in vtkPoints and
> set to datatype double, are specified in UTM coordinates. When zooming in
> close and rotating the the grid, the point locations jump around as if
> truncated to single precision.  Using the same data sets with a subtracted
> offset to bring the x,y locations down to single precision eliminates the
> problem.  Can anyone lend some insight as to why this might be happening?
> Is there a truncation issue in VTK or is it a product of the graphics
> board?  Any help would be greatly appreciated.
>
> Thank you,
> Rich McDonald
> Research Hydrologist
> USGS Geomorphology and Sediment Transport Laboratory
> 4620 Technology Drive, Suite 400
> Golden, CO 80403
> 303 278 7952
> rmcd at usgs.gov
>
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