[vtkusers] Problem displaying actors with large coordinates values ?

[pof]

David,
thanks for answering, eventhough it is not very optimistic for my problem.
At least, it will avoid me spending too much time on trying to solve 
this, as it may probably not be solved using any of the 2 options I 
mentionned.
Obviously, if an OpenGL Guru has an idea for this problem, he's welcome.
P.F.

> I've seen the effect before. As I recall it is caused by lack of
> precision in the GL library that VTK uses (24bits for X or something
> to that effect). I am not aware of a good solution. Perhaps someone
> else will chime in with one.
>
> David E DeMarle
> Kitware, Inc.
> R&D Engineer
> 28 Corporate Drive
> Clifton Park, NY 12065-8662
> Phone: 518-371-3971 x109
>
>
>
> On Mon, Jun 29, 2009 at 11:34 PM, pof<jd379252 at gmail.com> wrote:
>   
>> Dear vtk'ers,
>>
>> I need to display actors that are built from vtkPoints::New(VTK_DOUBLE) and
>> that have large coordinate values (typically in the range 1e6 to 1e7, coming
>> from Digital Elevation Model), although the scene extent (xmax-xmin,
>> ymax-ymin, zmax-zmin) is in the order of (1e3, 1e3, 1e3).
>>
>> When displaying such objects in a scene, everything looks fine at first
>> sight.
>> However, as soon as some rotation and zooming are applied with the mouse
>> action, the scene becomes less neat, and there are some random overlaps
>> (i.e. it is changing as the viewpoint is changed) between actors.
>>
>> So far, the only way I found to get rid off these nasty artifacts is to
>> perform a translation of the vtkPoints instance, such that its coordinates
>> values become much smaller.
>> However, I would really prefer to avoid such translation to save memory, as
>> I need to keep the original data (i.e. untranslated data points).
>>
>> To solve this, I'm thinking about some possibilities, so far unsuccessful:
>> - Perform the translation at the actor's level, but I have not found any
>> method to do that.
>> - Force the actor display to use 'double' reals as I guess it is presently
>> using 'float' reals (note that I'm already using 'double' vtkPoints instead
>> of 'float', though it hardly has any effect on the displayed artifacts)
>>
>> Does anybody has a clever idea or comment that could point me towards the
>> right direction?
>> Thanks,
>> P.F.
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>
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