public void smooth(float np) {
        smooth(np, 1);
    }
Smooth the terrain. For each node, its 8 neighbors' heights
are averaged and will influence node's new height
to the extent specified by <code>np</code>.

You must first load() the heightmap data before this will have any effect.

@param np
         To what extent neighbors influence the new height:
         Value of 0 will ignore neighbors (no smoothing).
         Value of 1 will ignore the node old height.
jme3-terrain/src/main/java/com/jme3/terrain/heightmap/AbstractHeightMap.java