void computeNormal() {
            // Cross-product 2 edges
            tmpV1.set(vertex[1].position).subtractLocal(vertex[0].position);
            tmpV2.set(vertex[2].position).subtractLocal(vertex[1].position);
            
            normal = tmpV1.cross(tmpV2);
            normal.normalizeLocal();
        }
Collapses vertices until the cost exceeds the given value.

Collapse cost indicates how much inaccuracy the
reduction causes. This generates the best LOD output, but the collapse
cost is implementation-dependant.
jme3-core/src/tools/java/jme3tools/optimize/LodGenerator.java