# Slicer IGT providing Stylus tool-tip as input in Fiducial Registation Wizard under "To fiducials"

**URL:** <https://discourse.slicer.org/t/slicer-igt-providing-stylus-tool-tip-as-input-in-fiducial-registation-wizard-under-to-fiducials/8562>\
**Category:** Support\
**Tags:** registration\
**Created:** [September 25, 2019, 1:23pm UTC](https://discourse.slicer.org/t/slicer-igt-providing-stylus-tool-tip-as-input-in-fiducial-registation-wizard-under-to-fiducials/8562 "2019-09-25T13:23:42Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![NormandRbert](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/normandrbert/32/2975_2.png) [@NormandRbert](https://discourse.slicer.org/u/NormandRbert)\
**Post date:** [September 25, 2019, 1:23pm UTC](https://discourse.slicer.org/t/slicer-igt-providing-stylus-tool-tip-as-input-in-fiducial-registation-wizard-under-to-fiducials/8562/1 "2019-09-25T13:23:42Z")

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I need to calibrate an O-arm imaging system to obtain an “OArmImageToOArmTransform” with an Optitrack tri-ocular camera. This is something we expect to perform infrequently hence I am trying to do this task using various module UIs instead of coding for now. We built a registration x-ray phantom with 20 divots for this task.  
We are creating a fiducial for each divot seen in a 3D image and/or orthogonal 2D image planes of the phantom using the “IGT”-\>“Fiducial Registration Wizard” under “From Fiducial”. We wish to create fiducials using an instrumented Stylus (Medtronic) using the “IGT”-\>“Fiducial Registration Wizard” under “To Fiducial”.

I am having issues passing the position of the navigated stylus tip when touching the phantom divots in the same order as I did for the 3D image. The Wizard allows fiducials to be populated via the current value of a transform, a feature that seems promising for my use. However, my StylusToReference transform is not the correct transform to populate the “To fiducials” because it is not centered on the tip. I think I need the transform StylusToReference . StylusToStylusTip. One might think that hardening might provide the desired information but as soon as I do that my resulting transform is a snapshot i.e. is not live anymore.

Looking for advice on how to do this via the UI but if not possible I am not adverse to writing a module and/or running some code in the Python interactor. Regards

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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:** [September 25, 2019, 2:00pm UTC](https://discourse.slicer.org/t/slicer-igt-providing-stylus-tool-tip-as-input-in-fiducial-registation-wizard-under-to-fiducials/8562/2 "2019-09-25T14:00:49Z")

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If you place StylusTipToStylus under the StylusToReference transform in the transform hierarchy (without hardening), you should then be able to place points at the StylusTip position in the Fiducial Registration Wizard.

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**Author:** ![NormandRbert](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/normandrbert/32/2975_2.png) [@NormandRbert](https://discourse.slicer.org/u/NormandRbert)\
**Post date:** [September 25, 2019, 2:34pm UTC](https://discourse.slicer.org/t/slicer-igt-providing-stylus-tool-tip-as-input-in-fiducial-registation-wizard-under-to-fiducials/8562/3 "2019-09-25T14:34:29Z")

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Resolved. Indeed you are right. I only realized this after submitting this post and before it was approved by the moderator 😊 Had I paid closer attention to the tutorials ([http://www.slicerigt.org/wp/user-tutorial/](http://www.slicerigt.org/wp/user-tutorial/)), I might have noticed my erroneous ways.