Performant mesh slicing in real time?

[OwenDavid]

Hi all,

We have a cuboid with one corner cut away to a smooth face. We then generate a slice in XY so normal to Z - the example shown in the image is at z=1.

Using the timer callback we then modulate the z position every frame to simulates the changing liquid level in a tank, for example.

At the moment we are removing and then generating a new slice object in every frame. But the (significant) impact on the scene update time suggest there must be a better way?

Is there an obvious solution to finding the liquid level of an irregular tank given the tank shape and liquid height?

Further, would it be possible to also generate a new mesh for the volume of liquid in the tank every frame performantly?

Thanks

[marcomusy]

Hope this example helps! I don't know if it's performant enough though...

from vedo import *

def func(w, evt=""):
    z = slider.value
    level = Plane(res=(50,50)).triangulate().pos(0,0,z)
    level.cut_with_mesh(tank, invert=False)
    level.compute_normals()
    level.lighting("off").c("blue3").alpha(0.5)
    ctank = tank.clone().cut_with_plane(normal="z", origin=(0, 0, z), invert=True)
    total = merge(ctank, level).compute_normals()#.flip_normals().reverse()   
    t2d.text(f"Water level: {z:.3f} m\nVolume: {total.volume():.4f} m:^3")
    plt.remove("Plane").add(level)


settings.default_font = "Roboto"

tank = Paraboloid().rotate_x(180)
tank.compute_normals().flip_normals().reverse()

tank.lighting("off").c("orange3").alpha(0.2)
t2d = Text2D()

plt = Plotter()
slider = plt.add_slider(func, 0, 1, value=0, title="Level", show_value=False)
plt.show(
    tank,
    t2d,
    axes=1,
    bg="orange9",
    bg2="blue9",
    viewup="z",
)
plt.close()

[OwenDavid]

Thanks, I will take a close look at this.

[OwenDavid]

Hi Marco,

I have been working on this recently.

We have another "tank" shape with curvature on one edge. The mesh looks reasonable and is loaded from a STL file. Upon loading the volume is computed correctly and the mesh is show to be closed.

We are using the faster cut_with_box() method to return the submerged volumes. We are capping the cut mesh using cap().

For the most part the new mesh is closed (with the user feedback showing a blue colour) but at several heights the capped mesh is open (with yellow feedback). How will this be impacting the volume calculations? It appears to be happening on several different meshes at arbitrary liquid heights.

Is this being caused by the quality of the imported mesh or are we missing a trick in the code?

The mesh under the cut looks quite ok...

What do you think?

from vedo import *

def func(widget, event):
    z = widget.value
    rho = 1.025
    
    #fwd tank
   

    fs_slice = tank.intersect_with_plane(normal=[0, 0, 1], origin=[0, 0, z]).alpha(0.25).c('blue').join()
    fs_slice.name = ("fs_slice")
    fs_slice.lw(3).wireframe().clean()
    plt.remove("fs_slice").add(fs_slice)

    sub_slice = fs_slice.clone().clean().triangulate().wireframe()
    sub_slice.name=("sub")
    #plt.remove("sub").add(sub_slice)

    xmin, xmax, ymin, ymax, zmin, zmax = tank.bounds()
    box_bounds = [xmin-100,xmax+100,ymin-100,ymax+100,z, zmax+100]
    ctank = tank.clone().cut_with_box(box_bounds, invert=True ).cap()
    ctank.name="CTank"
    ctank.lighting("off").c("blue3").alpha(0.05)
    ctank.clean().triangulate().compute_normals().wireframe()
  
    plt.remove("Plane").remove('CTank').add(ctank)
    
    t2d.text(
        (f"Water level: {z:.2f} mm\n"
        f"Surface area: {sub_slice.area()/1e6:.4f} m:^2\n"
        f"Submerged Volume: {ctank.volume()/1e9:.4f} m^3\n"
        f"Closed Volume: {ctank.is_closed()}")
    )

    if ctank.is_closed():
        print("ctank closed")
        tank.c('blue')
    else:
        print("ctank open")
        tank.c('yellow')
        


tank = Mesh("fwd.stl").c('grey').alpha(0.05)
tank.name = ("tank")
tank.compute_normals()
zmin,zmax = tank.bounds()[4:]

print(tank.volume()/1e9)

plt = Plotter()

slider = plt.add_slider(func, ceil(zmin), ceil(zmax), value=ceil(zmin), title="Level", show_value=True)
t2d = Text2D()

plt.show(
    tank,
    t2d,
    viewup='z',
    )```

[OwenDavid]

We turned the mesh.boundaries() on and we can see that the possible issue being shown by the purple lines. They appear at the edge of the cap/ on the liquid surface. Is there a way to resolve these issues?

[OwenDavid]

[marcomusy]

hi, I think it can be due to a precision issue as the vertices of the mesh exactly overlap with the cutting plane.

you can try to tilt a little bit the tank tank.rotate_y(1) and see if the problem persists..
also check out this simplified version which might be faster:

from vedo import *

def func(widget, event):
    z = widget.value

    # not needed, but shows how to slice
    # tankslice = tank.slice(normal=[0, 0, 1], origin=[0, 0, z]).rename("slice")
    # tankslice.lighting("off").c("blue4").alpha(0.5)

    xmin, xmax, ymin, ymax, zmin, zmax = tank.bounds()
    box_bounds = [xmin - 10, xmax + 10, ymin - 10, ymax + 10, z, zmax + 10]
    ctank = tank.clone(deep=False).cut_with_box(box_bounds, invert=True)
    ctank.clean().compute_normals().rename("Tank")
    area1 = ctank.area()
    ctank.cap()  # cap the top of the cut tank
    area2 = ctank.area()
    area = area2 - area1
    volume = ctank.volume()
    ctank.lighting("shiny").c("blue7").alpha(1)

    t2d.text(
        f"Surface area: {area:.4f} m:^2\n"
        f"Submerged volume: {volume:.4f} m:^3\n"
    )
    if ctank.is_closed():
        tank.c("blue")
    else:
        printc("tank open", c="r")
        tank.c("yellow")
    plt.remove("Tank").add(ctank)

tank = Paraboloid().rotate_x(180)
tank.compute_normals().flip_normals().reverse()
tank.lighting("off").c("grey").alpha(0.1)
zmin, zmax = tank.bounds()[4:]

t2d = Text2D(font="Calco", s=1.2)

plt = Plotter(axes=8)
slider = plt.add_slider(
    func,
    zmin,
    zmax,
    value=zmin,
    title="Water Level",
)
plt.show(tank, t2d, viewup="z", zoom=1.1)