public float[] createHeightSubBlock(float[] heightMap, int x,
                    int y, int side) {
        float[] rVal = new float[side * side];
        int bsize = (int) FastMath.sqrt(heightMap.length);
        int count = 0;
        for (int i = y; i < side + y; i++) {
            for (int j = x; j < side + x; j++) {
                if (j < bsize && i < bsize)
                    rVal[count] = heightMap[j + (i * bsize)];
                count++;
            }
        }
        return rVal;
    }
<code>createQuadPatch</code> creates four child patches from this quad.
jme3-terrain/src/main/java/com/jme3/terrain/geomipmap/TerrainQuad.java