# Creating a custom Annotation node in a Python scripted module

**URL:** <https://discourse.slicer.org/t/creating-a-custom-annotation-node-in-a-python-scripted-module/2331>\
**Category:** Development\
**Tags:** annotations\
**Created:** [March 15, 2018, 8:34pm UTC](https://discourse.slicer.org/t/creating-a-custom-annotation-node-in-a-python-scripted-module/2331 "2018-03-15T20:34:42Z")\
**Posts on this page:** 1\
**Showing post:** 5

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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:** [March 16, 2018, 6:00pm UTC](https://discourse.slicer.org/t/creating-a-custom-annotation-node-in-a-python-scripted-module/2331/5 "2018-03-16T18:00:59Z")

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Yes it is standard curved planar reformatting. The functionality is already available in Slicer, it just not easy to figure out how. It is described in detail here:

> [@Cross Sectional Area of a Ring](https://discourse.slicer.org/t/cross-sectional-area-of-a-ring/1015):
>
> I am looking to calculate the cross sectional area at multiple points around the ring (I tried to mark where I would like to slice the ring and measure the area using pairs of fiducials in the image below). I am not sure what the best method is as the orientation of the slice is constantly changing, so I’m just looking for an idea of what add-on or method would be best. Thank you!

So, you can find an example of positioning an object along a curve in Endoscopy module. I think this module uses the same method as I described above to constrain rotation around the curve direction vector. For vessels (and for any other significantly non-planar curve), I would use a Frenet-Serret frame ([SplineDrivenImageSlicer/Filters/vtkFrenetSerretFrame.h at master · djelouze/SplineDrivenImageSlicer · GitHub](https://github.com/jeromevelut/SplineDrivenImageSlicer/blob/master/Filters/vtkFrenetSerretFrame.h)) instead of a fixed constraining direction.

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