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

[Ken Martin]

I think Modified time is independent of the clock. I believe it is a 64bit
integer that starts at zero and goes up by one each time something is
modified by VTK. So maybe something else is going on here...

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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-- 
Ken Martin PhD
Distinguished Engineer
Kitware Inc.
28 Corporate Drive
Clifton Park NY 12065

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