compiling boundaries into a volume

Hello,

I've got a loop that outputs the coordinates of 3 segmented shapes in an image (using bwboundaries), and currently plot these over the original image.

For each image I have:

for k = 1:length(segments) %length of "segments" is normally 3

    boundary = segments{k};    
    x=boundary(:,2);
    y=boundary(:,1);
    plot(x, y, 'r', 'LineWidth', 2)

end

This image is part of a 3D dataset, so I have the X Y coordinates for the 3 objects for each slice in the image dataset (each original image slice is 512x512 pixels). Does anyone know how I might compile these coordinates into a seperate 3D image so I can view only my 3 segmented volumes? I somehow need to turn my boundary into a meshgrid

Thanks,

Jim