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Need help: Finding volume of unenclosed space

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Message 1 of 4
bhern027
1164 Views, 3 Replies

Need help: Finding volume of unenclosed space

Hi, I have a question that I have not been able to find an answer to through extensive research on this forum and through Google. I am an anthropologist studying activity-linked variations in the knee, more specifically, in the femur. I would like to find the volume of what is called the intercondylar notch (see the diagram attached). I have attached a couple representations/visualizations of the space that I am trying to determine the volume of. As you can see, the space is not entirely enclosed by bone, which is where most of my difficulty in calculating this volume is originating. Does anyone know if there is any possible way to get a computer program to (estimate) the intercondylar notch volume? My preferred program of use is Meshmixer, but willing to learn others if they are able to compute this volume.

 

Thanks for any input!

Brianna

2233_16_15-lower-part-femur.jpgthe volume I am trying to find, highlightedthe volume I am trying to find, highlightedThe same intercondylar volume filled for a different visualization Pt. IThe same intercondylar volume filled for a different visualization Pt. IThe same intercondylar volume filled for a different visualization Pt. IIThe same intercondylar volume filled for a different visualization Pt. II

3 REPLIES 3
Message 2 of 4
MagWeb
in reply to: bhern027

Are you interested in the volume's value only or do you need some mesh of that volume too?

Think you want to compare different bones. If so you might need some consistent way to compute such a volume. So what's the right way to construct it ?

Basically it's easy to get the not modified bone's volume (A) using ANALYSIS/Stability. Then deform your area of interest the desired way and get its volume (B). Now subtract B minus A...

 

There are different ways. The base is always a selection of the area of interest (compare attached image):

1. You could select and Edit/Extrude it with EndType "Flat"  to a fix offset.

2. You could select and run Edit/FitPrimitive with PrimitiveType "ConvexHull" and do a BooleanUnion of the resulting primitive and the bone (this requires additional steps...)

3. You could run Deform/Smooth with SmoothingType "PerGroupMembrane" on the selection

(a 4th (similar to 3rd) way would be to run Edit/EraseAndFill with SmoothType "SmoothMVC")

VolumeBySurface.png

Does something like that fit to your needs?



Gunter Weber
Triangle Artisan

Message 3 of 4
MagWeb
in reply to: MagWeb

OK, here's the workflow (IMO the best to be used) based on a convex hull ( for parameters' details see attached screenshots):

1. (optional but recommended) Run Modify/SmoothBoundary to get a smooth seam and a face group of the selected region;

2. hit Y to separate the selected group as a separate object;

3. SelectAll of the new object;

4. This selected run Edit/FitPrimitive, set its Type to ConvexHull and check CreateNewObject;

The convex hull doesn't give the precise value of the space enclosed by the separated surface of interest as it is convex on the interior side of the bone too. We need to attract this region of the hull to the original surface:

5. Hide all objects but the FitPrimitive result and run EDIT/GenerateFaceGroups. Your aim is to join all interior triangles of the hull to a single group. As there's a harsh edge between inside and outside regions a little adjustment of the AngleThresh should do the job.

6. Set the separated cavity as a target clicking the magnet icon in the object browser and select the interior group of the hull by double clicking it;

7. This selected run Edit/AttractToTarget;

8. Run EDIT/Stability to get the modified hull's volume;CavityVolume.png



Gunter Weber
Triangle Artisan

Message 4 of 4
nguyenhieu1
in reply to: MagWeb

Hello,

 

I am medical student, and I am working in a study which need to investigate the volume of concave surface. Could you guide me how to do it please? Thank you so much.

 

Sincerely, 

 

 

Model 1.png

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