Making a 3D volume out of splines

Hi! I am making 3D figures out of x y z coordinates. I used alphashape for this so I could also calculate the volume but alphashape creates 3D shapes which are bigger than they should be. I also used splines which creates the shape that the figures should have. However, I do not know how to make an actual 3D volume out of this like the alphashape does. An example: f.l.t.r scatterplot of the coordinates, alphashape and spline figure.

Does someone know how to make a 3D figure out of the spline figure? Or how to calculate the total volume out of this?

Thank you!

[KSSV]

What do you expect?

[Ellen]

My goal is to make a smooth correct 3D figure out of the provided coordinates. So for example, fill the figure created by the spline lines, but I don't know it that is possible. Other ideas are also very welcome.

Answer 1

[darova]

Try this

clc,clear

load Coordinates.txt
x = Coordinates(:,1);
y = Coordinates(:,2);
z = Coordinates(:,3);

plot3(x,y,z,'.r')
for z0 = min(z):1:max(z)
    ix = find(abs(z-z0)<0.3);       % find indices of level
    x1 = x(ix)-mean(x(ix));         % center data
    y1 = y(ix)-mean(y(ix));
    z1 = z(ix);
    [t,r] = cart2pol(x1,y1);        % convert to polar system
    [t2,ix1] = sort(t);             % order data by angle
    x2 = x1(ix1)+mean(x(ix));       % return to original position
    y2 = y1(ix1)+mean(y(ix));
        % interpolate data
    tt = [0; cumsum(hypot(diff(x2),diff(y2)))];
    t3 = linspace(0,tt(end));
    x3 = spline(tt,x2,t3);
    y3 = spline(tt,y2,t3);
    z3 = spline(tt,z1(ix1),t3);
    line(x3,y3,z3)
end
axis vis3d