[r,th] = meshgrid(10:15,0:180);
[x,y] = deal(r.*sind(th), r.*cosd(th));
z = x.^2+y.^2;
scatter(x(:),y(:),[],z(:),'fill'); axis equal off;

tri = delaunay(x,y);
trisurf(tri,x,y,z);  view(2); axis equal off;

A = alphaShape(x(:), y(:), z(:));