# IGT fiducial registration : How to have a fix coordinate system

**URL:** <https://discourse.slicer.org/t/igt-fiducial-registration-how-to-have-a-fix-coordinate-system/31448>\
**Category:** Support\
**Created:** [August 30, 2023, 12:54pm UTC](https://discourse.slicer.org/t/igt-fiducial-registration-how-to-have-a-fix-coordinate-system/31448 "2023-08-30T12:54:42Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![saeedeh\_lavasany](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/saeedeh_lavasany/32/7539_2.png) [@saeedeh\_lavasany](https://discourse.slicer.org/u/saeedeh_lavasany)\
**Post date:** [August 30, 2023, 12:54pm UTC](https://discourse.slicer.org/t/igt-fiducial-registration-how-to-have-a-fix-coordinate-system/31448/1 "2023-08-30T12:54:42Z")

</div>

Hello I am trying to use IGT fiducial registration to register a tool that position is tracked by an EMT sensor to a CT model.  
I’m using two EM sensors: one is called the “stylus,” and the other is named the “reference.”  
I followed the tutorial to register the stylus tip by aligning it with specific markers I selected on the CT scan.  
After completing the registration process, I incorporated the “Reference To CT” transformation into the hierarchy.

However, there’s an issue. Even though I attempt to transfer the information from the stylus sensor to the reference sensor, which is securely positioned on the phantom object, the transformation called “Reference To CT” becomes inaccurate when I manipulate the field generator. As a result, I lose the ability to visualize the stylus on the phantom object.

Would you please let me know whats the problem?

 ![Capture3](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/a/9/a921966d711a248c8dc4eceee381abaa0c1b7643.png)  
 ![Capture4](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/d/a/dade8638c953ad47f040a5155505e26f5e7e15a9.png)

 ![Capture1](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/c/d/cd5a49c6512b90ca1525f306874c4ec24a1f4431.png)  
 ![Capture2](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/d/d/ddf61083b91fbba8234725979f77b619f830a837.png)

---

<div class="post-metadata">

**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:** [August 30, 2023, 6:27pm UTC](https://discourse.slicer.org/t/igt-fiducial-registration-how-to-have-a-fix-coordinate-system/31448/2 "2023-08-30T18:27:20Z")

</div>

ReferenceToTracker is constantly being updated by Plus, overwriting the inverse.  
You can add TrackerToReference (or StylusToReference) in the Plus config file, and use one of those to transform the stylus.

---

<div class="post-metadata">

**Author:** ![saeedeh\_lavasany](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/saeedeh_lavasany/32/7539_2.png) [@saeedeh\_lavasany](https://discourse.slicer.org/u/saeedeh_lavasany)\
**Post date:** [August 31, 2023, 8:37am UTC](https://discourse.slicer.org/t/igt-fiducial-registration-how-to-have-a-fix-coordinate-system/31448/3 "2023-08-31T08:37:24Z")

</div>

Thank you for your reply. I implemented the transformation, and now everything is working perfectly.

---

<div class="post-metadata">

**Author:** ![Dr\_Ayush\_Shrivastava](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/dr_ayush_shrivastava/32/78794_2.png) [@Dr\_Ayush\_Shrivastava](https://discourse.slicer.org/u/Dr_Ayush_Shrivastava)\
**Post date:** [February 23, 2025, 6:23pm UTC](https://discourse.slicer.org/t/igt-fiducial-registration-how-to-have-a-fix-coordinate-system/31448/4 "2025-02-23T18:23:44Z")

</div>

How can i connect you , i need help.