public void buildShell(final double k, final double width) {
build(
new Function3D() {
public double eval(double x, double y, double z) {
x = Math.min(x, _lx - x);
y = Math.min(y, _ly - y);
z = Math.min(z, _lz - z);
double r = Math2.hypot(x, y, z);
return (Math.abs(k - r) < width / 2.) ? 1 : 0;
}
});
}
