Use linspace or colons to create one or three vectors to define your coordinate grid.
Then you can use ndgrid or meshgrid to expand that/those vector(s) to a full grid.
Now use element-wise operations (.* and ./ and .^) to compute . The logical operators < and > will work element-wise by default.
Now you have logical arrays where the combination of x,y,z is either valid or invalid. You can use logical indexing to either remove them, or mark a value array with NaN.
Now you have x y and z vectors, which you can input to a function like plot3 to show the pointcloid.