What is the missing factor in the code attached for calculating the area of a 3D surface

The below code is supposed to find the area of a surface by summing the area of each triangles. But while running the code the area id always turning out to be zero. Kindly suggest some solution to resolve this issue

T = delaunay(X,Y);

TO = triangulation(T,X(:),Y(:),Z(:));

trimesh(TO)

area = 0; %initialize the area

%loop over all the desired small triangles and accumulate the areas

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 triangl%e

if (a(:,3) > 0.000015 ) % for z>15 micron

if (a(:,1:2) > 0.000075) % for x & y > 75 micron

if (any((0.383*a(:,1)+ a(:,2) < 0.0000128725) & (0.383*a(:,2)+ a(:,1)) < 0.0000128725))

p1 = a(1,:);

p2 = a(2,:);

p3 = a(3,:);

area = area + 0.5 * norm(cross(p2-p1,p3-p1));

end

end

end

end

Answer 1

[Prudhvi Peddagoni]

Hi Anand S,

It seems that 2nd and 3rd if conditions are cancelling each other in the above code.

The second if condition is that the values of a(: ,1:2) should be greater than 0.000075 while the third if condition is that the value 0.383*a(: ,1) + a(: ,2) should be less than 0.0000128725.

But it shouldn’t be possible according to the second if condition as a(: ,2) alone has a value greater than 0.000075 which is greater than 0.0000128725. So the area is not getting updated.

Hope this helps.

[Anand S]

Hi Prudhvi Peddagoni,

Thanks for your input. I have updated the third condition like this

if (any((a(:,2) < -2.589970505*a(:,1)+ 0.0003212305608) & (a(:,2) < -0.386104783*a(:,1)+ 0.000124028656)))

Now I am getting non zero value for area.