# Design of rigid tracker for optical tracking

**URL:** <https://discourse.slicer.org/t/design-of-rigid-tracker-for-optical-tracking/18614>\
**Category:** Development\
**Tags:** slicerigt\
**Created:** [July 10, 2021, 11:47am UTC](https://discourse.slicer.org/t/design-of-rigid-tracker-for-optical-tracking/18614 "2021-07-10T11:47:30Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![drvarunagarwal](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/drvarunagarwal/32/8914_2.png) [@drvarunagarwal](https://discourse.slicer.org/u/drvarunagarwal)\
**Post date:** [July 10, 2021, 11:47am UTC](https://discourse.slicer.org/t/design-of-rigid-tracker-for-optical-tracking/18614/1 "2021-07-10T11:47:31Z")

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Hi,

I am trying to setup optitrack duo for optical tracking via slicer IGT.  
I am using motive to design tracker as guided in the plustoolkit guide.

My question is regarding pivot point of the tracker.

The reflective spheres are tracked by camera and motive recognizes these and by default the pivot point is in the centre of geometry.  
However the point at which the tracker attaches to tool is somewhat away from this exact centre of geometry.  
Motive allows to change the pivot point of the tracker.

Should the pivot point of the geometry be this default centre point? or should it coincide with the point that the geometry attaches to the tool?

 ![IMG_3990](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/3/8/3873fc107648e741e3abace9daeabc0b6e00d706.jpeg)

which point In the image above, point A, B or C, should be set as pivot point? or it doesn’t matter?

Is this effect taken into account by the tool calibration algorithm? Does this have any effect on accuracy?

I hope I am clear on my question

Please advise.

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**Author:** ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)\
**Post date:** [July 14, 2021, 3:39am UTC](https://discourse.slicer.org/t/design-of-rigid-tracker-for-optical-tracking/18614/2 "2021-07-14T03:39:56Z")

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It does not matter how Motive chooses origin and axis directions of your marker, because you can get the transformation from the marker to your tooltip using Pivot calibration module of SlicerIGT extension (see [U-11 SlicerIGT tutorial](http://www.slicerigt.org/wp/user-tutorial/)).

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**Author:** ![drvarunagarwal](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/drvarunagarwal/32/8914_2.png) [@drvarunagarwal](https://discourse.slicer.org/u/drvarunagarwal)\
**Post date:** [July 14, 2021, 3:56am UTC](https://discourse.slicer.org/t/design-of-rigid-tracker-for-optical-tracking/18614/3 "2021-07-14T03:56:09Z")

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thanks a lot for the guidance