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Measuring surface area on parts of a 3D scan

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Message 1 of 4
leung_chinghei55
208 Views, 3 Replies

Measuring surface area on parts of a 3D scan

Hello, I am studying marine biology in university and I am trying to measure the surface area of a coral fragment that is covered by living tissue. I have tried to do that using the following steps:

 

1. Flip the 3D model using EDIT transform

Screenshot 2024-05-18 130033.png

 

2.Align the 3D model to the plane using EDIT/align

Screenshot 2024-05-18 130133.png

 

3. Isolate the area of interest by using the SELECT tool and pressing "Y"

Screenshot 2024-05-18 161508.png

4. Run ANALYSIS/stability to obtain surfance area

Screenshot 2024-05-18 161630.png

 

I have tried to run ANALYSIS/inspection before getting the surface area but parts of the area I am interested in are flattened. 

Screenshot 2024-05-18 162102.png

 

Is there other way that I should use to get an accurate measurement of the surface area from a section of a 3D model? Thank you

3 REPLIES 3
Message 2 of 4
MagWeb
in reply to: leung_chinghei55

If you just want to get the surface area you don't need step 1 and 2

Your strategy in step 3 and 4  (isolating the area of interest via SELECT and Separate("Y") and running ANALYSIS/Stability) is the only way in MM to get a partial surface area. Basically it should return the sum of all separated triangles' areas.

Did you get some unexpected results?

 

Your attempt to fill  the open boundary of the separated surface via ANALYSIS/Inspector gives self intersections in your case but might construct a closed volume in other cases.  Anyhow: It adds an additional surface area  (the infill) ...

 

BTW: You might want to hide the printer rendering. See menu:View>ShowPrinterBed. Click it to get rid of it.



Gunter Weber
Triangle Artisan

Message 3 of 4
leung_chinghei55
in reply to: MagWeb

Thank you very much! The values for the surface area were not very different from what I expect when I am using this workflow but I was worried I might be using the wrong method since the values for the volume of the 3D model were negative. Would the values for the surface area still be accurate when the value for the volume is negative?

Message 4 of 4
MagWeb
in reply to: leung_chinghei55

An object's volume runs into negative values if the space included by triangles with normals pointing outwards is smaller than the space included by triangles with normals pointing inwards.

 

A: If you did a cube 1x1x1 its surface area is 6 while its volume is 1. In MM it appears rendered with the set Shader material.

B: If you SelectAll of the cube and do Edit/FlipNormal it gets that pink stripes pattern. Now the normals point inwards. Now the surface area still is 6 while the volume is negative (-1).

 

Calculating the volume of an object with several surfaces MM sums all volumes and surface areas. If you combine cubeA and cubeB to a single object its volume is zero ( 1 + (-1) ) while its surface is 12 

If B is bigger than A the volume result will be negative.

 

Now if you isolated a partial surface and run Stability MM needs to "think" a closed open boundary  to calculate a volume.

E.g.: If you separated 5 sides of cube A the volume still is 1 while the surface area is 5

On more complex shapes the infill might result in  self intersections > this means you get positive and negative partial volumes > the total sum might be negative.

Instead the surface area is always a sum of planar triangle areas ignoring normal directions.

 



Gunter Weber
Triangle Artisan

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