# ALPACA "What is the Target landmark set used for?"

**URL:** <https://discourse.slicer.org/t/alpaca-what-is-the-target-landmark-set-used-for/39648>\
**Category:** Support\
**Created:** [October 11, 2024, 8:43am UTC](https://discourse.slicer.org/t/alpaca-what-is-the-target-landmark-set-used-for/39648 "2024-10-11T08:43:32Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Chuan](https://avatars.discourse-cdn.com/v4/letter/c/4da419/32.png) [@Chuan](https://discourse.slicer.org/u/Chuan)\
**Post date:** [October 11, 2024, 8:43am UTC](https://discourse.slicer.org/t/alpaca-what-is-the-target-landmark-set-used-for/39648/1 "2024-10-11T08:43:32Z")

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Hi,  
I have a question regarding on the option of “Target landmark set (Optional)”,  
does anyone know what is this used for?  
Since ALPACA can generate new landmark on Target model, why there is this option that allowing user to put target landmark set?

Basically, I need the wrapped source model instead of caring about the landmarks. Do you think whether I input target landmark set here or not will influence the final wrapped source model during the “morphing” stage from source model towards target model?

Best regards,  
Chuan

![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/e/a/ea426048abeff36f90991aa1eddfb19ec1a4b4ce.png)

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**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:** [October 11, 2024, 3:36pm UTC](https://discourse.slicer.org/t/alpaca-what-is-the-target-landmark-set-used-for/39648/2 "2024-10-11T15:36:50Z")

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If you create do have a target landmark set, you can set that as a reference in this field and ALPACA will calculate the root mean square between that reference and the estimated landmark position.

RMS can be helpful when you are trying to optimize ALPACA parameters in an objective way.

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**Author:** ![Chuan](https://avatars.discourse-cdn.com/v4/letter/c/4da419/32.png) [@Chuan](https://discourse.slicer.org/u/Chuan)\
**Post date:** [October 11, 2024, 6:19pm UTC](https://discourse.slicer.org/t/alpaca-what-is-the-target-landmark-set-used-for/39648/3 "2024-10-11T18:19:54Z")

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I see, thank you very much!