# Detect when OpenIGTlink streamed transform no longer updated

**URL:** <https://discourse.slicer.org/t/detect-when-openigtlink-streamed-transform-no-longer-updated/20580>\
**Category:** Development\
**Tags:** python, openigtlink\
**Created:** [November 11, 2021, 2:53pm UTC](https://discourse.slicer.org/t/detect-when-openigtlink-streamed-transform-no-longer-updated/20580 "2021-11-11T14:53:14Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![atracsys-sbt](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/atracsys-sbt/32/11434_2.png) [@atracsys-sbt](https://discourse.slicer.org/u/atracsys-sbt)\
**Post date:** [November 11, 2021, 2:53pm UTC](https://discourse.slicer.org/t/detect-when-openigtlink-streamed-transform-no-longer-updated/20580/1 "2021-11-11T14:53:15Z")

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Hi,  
I stream tracking data to Slicer via OpenIGTlink, but I would like to be able to detect (i.e. emit an event) when tracking is no longer updated (e.g. the tracked object goes out of range).  
I have looked at what methods are available for vtkMRMLLinearTransformNode, but found nothing conclusive.  
Thanks  
S.

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**Author:** ![Sunderlandkyl](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/sunderlandkyl/32/79987_2.png) [@Sunderlandkyl](https://discourse.slicer.org/u/Sunderlandkyl)\
**Post date:** [November 11, 2021, 3:07pm UTC](https://discourse.slicer.org/t/detect-when-openigtlink-streamed-transform-no-longer-updated/20580/2 "2021-11-11T15:07:46Z")

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You might want to look at the Watchdog module in SlicerIGT. It can monitor any number of nodes, and will trigger a ModifiedEvent on the Watchdog node if their status changes. The status of individual nodes can be checked with vtkMRMLWatchdogNode::GetWatchedNodeUpToDate().

If you’re using Plus, and SendValidTransformsOnly is “FALSE”, then you can check the TransformStatus attribute on the TransformNode which is sent over OpenIGTLink as metadata.

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<div class="post-metadata">

**Author:** ![atracsys-sbt](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/atracsys-sbt/32/11434_2.png) [@atracsys-sbt](https://discourse.slicer.org/u/atracsys-sbt)\
**Post date:** [November 12, 2021, 9:12am UTC](https://discourse.slicer.org/t/detect-when-openigtlink-streamed-transform-no-longer-updated/20580/3 "2021-11-12T09:12:54Z")

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> [@Sunderlandkyl](#):
>
> TransformStatus

Since I am indeed using Plus, I opted for the second solution and it works like a charm, thanks !