@Override
    public float getInterpolatedHeight(float x, float z) {
        float low, highX, highZ;
        float intX, intZ;
        float interpolation;

        low = getScaledHeightAtPoint((int) x, (int) z);

        if (x + 1 >= size) {
            return low;
        }

        highX = getScaledHeightAtPoint((int) x + 1, (int) z);

        interpolation = x - (int) x;
        intX = ((highX - low) * interpolation) + low;

        if (z + 1 >= size) {
            return low;
        }

        highZ = getScaledHeightAtPoint((int) x, (int) z + 1);

        interpolation = z - (int) z;
        intZ = ((highZ - low) * interpolation) + low;

        return ((intX + intZ) / 2);
    }
<code>getInterpolatedHeight</code> returns the height of a point that
does not fall directly on the height posts.

@param x
           the x coordinate of the point.
@param z
           the y coordinate of the point.
@return the interpolated height at this point.
jme3-terrain/src/main/java/com/jme3/terrain/heightmap/AbstractHeightMap.java