# Ignore nodes when placing fiducial?

**URL:** <https://discourse.slicer.org/t/ignore-nodes-when-placing-fiducial/17014>\
**Category:** Support\
**Created:** [April 9, 2021, 3:44pm UTC](https://discourse.slicer.org/t/ignore-nodes-when-placing-fiducial/17014 "2021-04-09T15:44:53Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![hherhold](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/hherhold/32/12199_2.png) [@hherhold](https://discourse.slicer.org/u/hherhold)\
**Post date:** [April 9, 2021, 3:44pm UTC](https://discourse.slicer.org/t/ignore-nodes-when-placing-fiducial/17014/1 "2021-04-09T15:44:54Z")

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Normally when you interactively place a fiducial in the 3D view, the cursor/placement fiducial jumps to the intersection point closest to the camera of whatever is visible. For example, let’s say I have a body with a skeleton. I have a segment for the skin and a segment for the bones. If I turn the opacity down for the skin so I can see the bones, then I try to place a fiducial/markup point on the bones, it will jump to the skin as it’s the point nearest to the camera that’s visible.

Is it possible to force placement to a single segment only, such that it will ignore all other segments? That is, for the above example, can I force intersection tests to only be on the bones and ignore the skin?

Thanks!

-Hollister

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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:** [April 14, 2021, 5:27am UTC](https://discourse.slicer.org/t/ignore-nodes-when-placing-fiducial/17014/2 "2021-04-14T05:27:05Z")

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You cannot exclude individual segments from picking in 3D views, but you can exclude model nodes. After exporting your segmentation to model nodes (and hiding the segmentation) turn off `Selectable` property for the skin model by this command:

```python
getNode('skin').SetSelectable(False)

```

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**Author:** ![hherhold](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/hherhold/32/12199_2.png) [@hherhold](https://discourse.slicer.org/u/hherhold)\
**Post date:** [April 14, 2021, 11:04am UTC](https://discourse.slicer.org/t/ignore-nodes-when-placing-fiducial/17014/3 "2021-04-14T11:04:48Z")

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Oh, excellent - that’s perfect.

Thanks!