MATLAB: Clipping 3D mesh along boundary, interp1 problem

Question

Hello everyone,

I'm currently trying to cut off parts of a 3D mesh that lie outside of a certain threshold. To do so, I use interp1 to check if a point on the grid is above or below my threshold. My upper and lower limit is created using the boundary function on a set of points as shown in the first figure (X-Y view).

I set every point that is outside of the boundary to NaN with following code, where xm,ym,zm are the matrices generating the mesh, lower/upper contain the points from the boundary function, so that x(lower),y(lower) forms the lower border.

for i=1:size(zm,1)
    for j=1:size(zm,2)
        dyl=interp1(x(lower),y(lower),xm(i,j));
        dyu=interp1(x(upper),y(upper),xm(i,j));
        if ym(i,j)-dyl<0 || ym(i,j)-dyu>0
            zm(i,j)=NaN;
        end
    end
end

After setting all the values to NaN the following mesh remains.

To me it looks like the code worked at least in some places, but I cant figure out what causes the steep cuts along the upper border. My guess is that interp1 has problems giving interpolated values where the boundary has sharp bends. I tried using polyfit to compare the y-values to a fit function, both using boundary and convhull for the borders, but the results were not usable.

Can anyone see the problem here and is there a different/better way to do this?

Thanks for your help!

Answer 1

Check inpolygon ....with this you should be able to tell whether the given point lies inside or outside the given closed region.