@Override
    public void write(JmeExporter ex) throws IOException {
        super.write(ex);
        OutputCapsule capsule = ex.getCapsule(this);
        capsule.write(heightStickWidth, "heightStickWidth", 0);
        capsule.write(heightStickLength, "heightStickLength", 0);
        capsule.write(heightScale, "heightScale", 0);
        capsule.write(minHeight, "minHeight", 0);
        capsule.write(maxHeight, "maxHeight", 0);
        capsule.write(upAxis, "upAxis", 1);
        capsule.write(heightfieldData, "heightfieldData", new float[0]);
        capsule.write(flipQuadEdges, "flipQuadEdges", false);
    }
Uses Bullet Physics Heightfield terrain collision system. This is MUCH faster
than using a regular mesh.
There are a couple tricks though:
   -No rotation or translation is supported.
   -The collision bbox must be centered around 0,0,0 with the height above and below the y-axis being
   equal on either side. If not, the whole collision box is shifted vertically and things don't collide
   as they should.

@author Brent Owens
jme3-jbullet/src/main/java/com/jme3/bullet/collision/shapes/HeightfieldCollisionShape.java