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Newbie at blender - I am an anthropologist working on my dissertation. Seeking someone to help me develop a reliable (read: CONSISTENT) way to find the volume of this incomplete space on the distal femur. The space I reference is between the two round parts called condyles. I have tried this by making a convex hull, and through various means solidifying it & finding the volume of that object on Meshmixer but get different numbers each time I repeat this on the same 3D model. Unsure if I need to add an edge detection method or something. Can anyone help me with a more reliable method? Will give authorship credit on ALL future publications utilizing your method(s). I can provide .obj file(s) upon request. TIA

Edit - in regards to where the notch/fossa parameters are: there is a ridge along the inside of each condyle and the upper and lower aspect that I have attempted to outline. What I was hoping was there might be some way to have Blender fill in a mesh within this loop (similar to the grid fill function) that I might be able to get it to project points downwards to the actual bone scan which I then could solidify and take the volume of. However, I am not sure if this could feasibly work in Blender or if this is even feasible. image of femur bone enter image description here enter image description here enter image description here

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    $\begingroup$ May be a duplicate of blender.stackexchange.com/questions/63113/… You may also have/want to bisect the mesh to end up with just the bone head. I can walk through it and make sure it works, but not tonight. $\endgroup$
    – TheLabCat
    Commented Aug 31, 2022 at 4:13
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    $\begingroup$ This is a very irregular shape, you want the volume of the intercondylar fossa if I understand the question correctly. But where exactly do you want the volume to be measured? Where does the incomplete space begin/end? And depending on the resolution of your geometry just small variations of the enclosed space can make much difference in the results. $\endgroup$
    – Gordon Brinkmann
    Commented Aug 31, 2022 at 6:49
  • $\begingroup$ Please add the information that Gordon Brinkmann asked about, as otherwise it will be difficult to provide an accurate answer. Just a heads up, this question is very specific and Blender's Stack Exchange is meant as a Q&A that is useful to other users as well. Other moderators and users might therefore vote to close this question as "too specialized". $\endgroup$
    – Robert Gützkow
    Commented Aug 31, 2022 at 12:33
  • $\begingroup$ I edited the question title to reflect what's being asked, so that people can see what you want to know. The info previously contained in the title seems to also be present in the body, so I think that should be fine. If you disagree, feel free to edit the question back. I don't agree with others that this is a duplicate, but the tricky part is defining the bounds of the condyles, as G Brinkmann has suggested. $\endgroup$
    – Nathan
    Commented Aug 31, 2022 at 17:53
  • $\begingroup$ @TheLabCat - I went to the page you suggested and I don't think this is a duplicate, I know I need to solidify my bone mesh to get a volume, but I don't want the volume of the bone that is there, I actually want the best-fit (computer estimated) volume of the space that is between the two condyles. $\endgroup$
    – Brianna H
    Commented Aug 31, 2022 at 20:59

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This post is really just a 'suggestion of concept'. It would be interesting to see whether this method of selection, or some refinement of it, yields volume-measurements which are comparable between your samples, in a way which is useful to you.

The strategy is similar to Ambient Occlusion shading. It's to fire a set of rays from outward-facing hemispheres distributed the mesh, and test for hits on the mesh itself. Points which can 'see' the mesh are preserved, and the Convex Hull taken of those:

enter image description here

The volume could be taken of the resulting solid, by one of the methods already suggested in the commentary.

enter image description here

If it begins to show promise, then it might be worth coding / noding up, to suit your workflow.

(Blender 3.2b)

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    $\begingroup$ Hi @Robin Betts - thank you for your suggestion! Let me play around with this and I will get back to you :) I appreciate your time. $\endgroup$
    – Brianna H
    Commented Aug 31, 2022 at 21:06
  • $\begingroup$ Hi @BriannaH ! I've used half an icosphere in this example, for economy. Variations might include subdividing the icosphere more or less , using UV hemispheres instead, or even creating shapes which bias the sample-rays, and making a count of hits rather than a simple on-off switch. All to be considered if this isn't completely hopeless. $\endgroup$
    – Robin Betts ♦
    Commented Aug 31, 2022 at 21:38
  • $\begingroup$ @BriannaH Hello and welcome. This site is not a regular forum, we generally upvote the post that helped you. If you feel it completely solved your issue consider marking it as accepted. $\endgroup$
    – Duarte Farrajota Ramos ♦
    Commented Sep 5, 2022 at 19:49

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