Calculating a volume of a custom mesh using mesh.volume() doesn't work properly

Hi, I’m currently trying to build tubes and tubelike meshes, that might branch, etc. (I’m aware that there is a Tube shape in the Vedo library). I want to cut them and cap them at the places where they have opened up after cutting.
Additionally, I would like to calculate the total volume enclosed by the mesh before and after the procedure. Here’s an example below:

from vedo import *
import math

r = 1
coord_start_z = 0
coord_end_z = 1
angle = 0
number_of_vertices = 520
start_x = 0
start_y = 0
coordinates_all = []


for i in range(0,number_of_vertices):
    angle = (i/number_of_vertices)*2*3.141592653589793
    coord_x = start_x + r * math.cos(angle)
    coord_y = start_y + r * math.sin(angle)

    coordinates_all.append((coord_x,coord_y,coord_start_z))
    coordinates_all.append((coord_x,coord_y,coord_end_z))

faces = []
faces_base_start = [i for i in range(0,number_of_vertices*2) if i%2 == 0]
faces_base_end = [i for i in range(0,number_of_vertices*2) if i%2 != 0]
for i in range(0,number_of_vertices):
        faces_start = []
        if i + 1 == number_of_vertices:
            faces.append((i*2,i*2+1,1,0))
        else:
            faces.append((i*2,i*2+1,i*2+3,i*2+2))
        
faces.append(tuple(faces_base_start))
faces.append(tuple(faces_base_end))

tube =  Mesh([coordinates_all,faces])
cut_tube = tube.clone().cutWithPlane(origin=(0, 0, 0), normal=(1, 0, 0))
capped_cut_tube = cut_tube.clone().cap()
capped_cut_tube.c('r',alpha=0.5)

print('Volume of the original tube is: ' + str(tube.volume()))
print('Volume of the cut and capped tube is: ' + str(capped_cut_tube.volume()))

show(tube,axes=1,at=0,shape=(2,1))
show(capped_cut_tube,axes=1,at=1,shape=(2,1))

Unfortunately, the volume of the first tube is computed as 0 (it should be around 3.141592) and the second one is incorrectly calculated as well (0.8742, even though the volume is roughly halved by the split).

What could be the issue here?

[lukablagoje]

Thanks!

[marcomusy]

I actually did not think of the possibility to sweep a line to create tubes:

from vedo import *

pts = Circle().points().tolist()
ln1 = Line(pts+[pts[0]])

surf1 = ln1.sweep(( 2,0.2,3), res=3).c('red3')

pts = ln1.points().tolist()
ln2 = Line(pts+[pts[0]])
surf3 = ln2.sweep((3,0.3,3), res=3).c('green3') # the right branch

surf2 = ln1.sweep((-2,0.2,3), res=3).c('blue3')
surf2.cutWithMesh(surf3) # this cuts, but must increase resolution (res)

show(surf1, surf2, surf3, axes=1).close()

m = merge(surf1, surf2, surf3)
print(m.bounds())

################# second solution/approach
line1 = Line([[0,0,0],[2,.2,3],[-2,-.1,6]], lw=4).c('red4')
line2 = Line([[2,.2,3],[3,-.1,6]], lw=4)
lines = merge(line1, line2)
tube = lines.implicitModeller(distance=0.3, res=(100,50,100), bounds=m.bounds()).smooth()
tube.flat().lw(0.1).alpha(0.5)

show(line1,line2, tube, axes=1)

But probably the second solution is what you are after (but this one can become very memory-consuming for large networks: