# How to measure surface area in mm^ generated using triangulaiton of a 3D object model by Matlab

2 views (last 30 days)
M.S. Khan on 24 Aug 2020
Edited: Bruno Luong on 26 Aug 2020
I have geneated Cone Model. The cone was generated using radius 78 mm and height 188.4 mm. Using trimesh(), i have triangulated it to measured its suface area. Please help me how to measusre caliberation factor to approxite it surface area or volume. i will be very thankfull for your cooperation and guidance.
Attached are coordinates and the figure of the cone. Thanks for the guidance of KSSV and Uday.
Regards,
bx = Boundary(:,1) ; by = Boundary(:,2) ; bz = Boundary(:,3) ;
T = delaunay(bx, by)
TO = triangulation(T, bx(:),by(:),bz(:));
area = 0;
for i = 1:size(TO.ConnectivityList,1) %the number of rows gives the number of triangles produced
a = TO.Points(TO.ConnectivityList(i,:),:); %this gives the 3 vertices of the ith triangle
if any(a(:,3) > max(bz))
continue;
end
%extract the three vertices
p1 = a(1,:);
p2 = a(2,:);
p3 = a(3,:);
format compact
area = area + 0.5 * norm(cross(p2-p1,p3-p1)); %calculate the area of the small triangle and add with previous result
end
--------------------------------
The above code gives me surface area = 47975.3181943477. This represent pixel, right.
How to measure the real surface area by applying caliberation factor. Please help me how to measure caliberation factor because i am new in this field.
The cone is orginally genereated having radius 78 mm and height 188.4 mm.

Bruno Luong on 26 Aug 2020
I don't know where you get the first formula from. It doesn't look right.
The second formula where I gave you is the correct one.
And beside this is not the question asked, please open the new one if you still have issue with computing the volume.
M.S. Khan on 26 Aug 2020
volume of the cone = surface area * height
Is it not a correct formula?
Bruno Luong on 26 Aug 2020
No. This is the correct formula
V = 1/3 * pi * r^2*h
anything different than that is not.