# Adding a missing landmark to a mrk.json file 

**URL:** <https://discourse.slicer.org/t/adding-a-missing-landmark-to-a-mrk-json-file/42400>\
**Category:** Support\
**Tags:** markups\
**Created:** [April 1, 2025, 4:33pm UTC](https://discourse.slicer.org/t/adding-a-missing-landmark-to-a-mrk-json-file/42400 "2025-04-01T16:33:06Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![grega](https://avatars.discourse-cdn.com/v4/letter/g/96bed5/32.png) [@grega](https://discourse.slicer.org/u/grega)\
**Post date:** [April 1, 2025, 4:33pm UTC](https://discourse.slicer.org/t/adding-a-missing-landmark-to-a-mrk-json-file/42400/1 "2025-04-01T16:33:06Z")

</div>

I have a point on a bone that i’m landmarking that isn’t present on all the samples in my data set. To be able to run GPA+PCA analysis I need to have a consistent number of points for each sample, so is there a way I can add a “missing landmark” so I can keep the number of landmarks the same, while not impacting the PCA slicer gives me?

---

<div class="post-metadata">

**Author:** ![muratmaga](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/muratmaga/32/3622_2.png) [@muratmaga](https://discourse.slicer.org/u/muratmaga)\
**Post date:** [April 3, 2025, 4:15am UTC](https://discourse.slicer.org/t/adding-a-missing-landmark-to-a-mrk-json-file/42400/2 "2025-04-03T04:15:46Z")

</div>

You can. However that landmark needs to be in the same spot (e.g., if it is the 3rd landmark, it has to be in that position like every other dataset).

See this tutorial section on how to designate a control point (landmark) as missing: [Tutorials/Markups\_1 at main · SlicerMorph/Tutorials · GitHub](https://github.com/SlicerMorph/Tutorials/tree/main/Markups_1#the-control-points-menu)

When you are setting your GPA analysis do not forget to enter the index (in my example 3) of that landmark into the `exclude landmarks` field. Otherwise your analysis won’t work.

(To clarify, you are technically designating the landmark as **SKIPPED** -as opposed to missing- in Slicer. THen you are telling GPA module to exclude it).