# Draw specific dimension

**URL:** <https://discourse.slicer.org/t/draw-specific-dimension/22934>\
**Category:** Support\
**Created:** [April 13, 2022, 12:19pm UTC](https://discourse.slicer.org/t/draw-specific-dimension/22934 "2022-04-13T12:19:06Z")\
**Posts on this page:** 1\
**Showing post:** 4

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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 13, 2022, 6:06pm UTC](https://discourse.slicer.org/t/draw-specific-dimension/22934/4 "2022-04-13T18:06:42Z")

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For any measurement types that are not supported already by an existing markup, you can create your own custom markup by a little Python scripting. The idea is that you use markups to position models. You can add an observer to the markup so that if a control point position is changed then you get notified and you update the model.

There are a few simple examples in the script repository, as [this](https://slicer.readthedocs.io/en/latest/developer_guide/script_repository.html#define-edit-a-circular-region-of-interest-in-a-slice-viewer). There is a more complex example here:

> [@Drawing Circle on CT Image](https://discourse.slicer.org/t/drawing-circle-on-ct-image/20387/3):
>
> You can also use 2 points of a markups fiducial node to specify a circle by copy-pasting a few lines of code to into the Python console as shown in [this example](https://slicer.readthedocs.io/en/latest/developer_guide/script_repository.html#define-edit-a-circular-region-of-interest-in-a-slice-viewer). I’ve created a modified script that allows you to place 2 circles by specifying 6 points on the circumference: [Compute bone axis in 3D Slicer by specifying two circles. · GitHub](https://gist.github.com/lassoan/99514fb5edf98e1e3dda926253dc9742) You can use this by placing one fiducial list containing 6 points then copy-pasting into the Python console: [[Custom interactive measurement using P…](https://www.youtube.com/watch?v=1DG3y1TqWvw)

I would recommend using a vtkSphereSource for drawing a circle because then you don’t need to worry about orientation.

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