[vtk-developers] Rendering Corruption Due to PC Time Change

Will Schroeder will.schroeder at kitware.com
Mon May 8 07:44:42 EDT 2017


I love this bug! The more the esoteric bugs we have time to chase, my
obviously biased conclusion is that the better the quality of VTK's core
functionality is :-)

I would enjoy seeing screenshots. I assume they would be public and we
would be able to use them elsewhere? Of course with appropriate credit...

Best,
W

On Mon, May 8, 2017 at 7:25 AM, Paul <paul at 3dimageautomation.com.au> wrote:

> Hi,
>
> We are using VTK in a 3D LiDAR based mining automation application which
> operates continuously.
>
> VTK in medical application is great but VTK controlling the world’s
> largest autonomous machine is interesting for engineering types.
>
> If anyone is interested we can post some screenshots.
>
>
>
> Many of the vtk developers will remember the vtk code impact of our
> original issue with overflow of ModifiedTime on a Win64 build.
>
> Thanks again for the effort, it was certainly a relief as it was so
> critical for our application success.
>
>
>
> Subsequent to the overflow fix the application has been running without
> issues on two system equipped with dual Xeon processors.
>
> However one system with a four core i7 was having rendering issues at
> intervals of a week or more.
>
> Our initial thoughts was that the issue was related to high processor
> loading.
>
>
>
> It turns out that the issue is related to ModifiedTime.
>
> Rendering breaks if the PC time is changed in a negative direction.
>
>
>
> It took us some time to discover this.
>
> The i7 system is running Windows 7 and the Windows Time service was in the
> Scheduled Tasks to run once a week on Sunday morning.
>
> Vtk rendering only breaks if the time synchronisation has a negative
> correction.
>
> This can be reproduced by manually changing the PC time backwards.
>
>
>
>
>
> Q. Could this be resolved by making ModifiedTime independent of the PC
> clock.
>
> We run a PLC (real time automation controller) in kernel mode on the same
> platform.
>
> PLC’s are used in time critical applications such as motion
> synchronisation and use a SystemTime that does not jump.
>
> I am not sure what mechanism the PLC uses but suspect that the time is
> initialised to the PC time on application start and then incremented at
> 100nS intervals (the timer resolution).
>
>
>
> Paul
>
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-- 
William J. Schroeder, PhD
Kitware, Inc. - Building the World's Technical Computing Software
28 Corporate Drive
Clifton Park, NY 12065
will.schroeder at kitware.com
http://www.kitware.com
(518) 881-4902
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