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With inspiration from other libraries
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.math3.geometry.partitioning;
import org.apache.commons.math3.geometry.Space;
/** Visitor building boundary shell tree.
*
* The boundary shell is represented as {@link BoundaryAttribute boundary attributes}
* at each internal node.
*
* @param Type of the space.
* @since 3.4
*/
class BoundaryBuilder implements BSPTreeVisitor {
/** {@inheritDoc} */
public Order visitOrder(BSPTree node) {
return Order.PLUS_MINUS_SUB;
}
/** {@inheritDoc} */
public void visitInternalNode(BSPTree node) {
SubHyperplane plusOutside = null;
SubHyperplane plusInside = null;
NodesSet splitters = null;
// characterize the cut sub-hyperplane,
// first with respect to the plus sub-tree
final Characterization plusChar = new Characterization(node.getPlus(), node.getCut().copySelf());
if (plusChar.touchOutside()) {
// plusChar.outsideTouching() corresponds to a subset of the cut sub-hyperplane
// known to have outside cells on its plus side, we want to check if parts
// of this subset do have inside cells on their minus side
final Characterization minusChar = new Characterization(node.getMinus(), plusChar.outsideTouching());
if (minusChar.touchInside()) {
// this part belongs to the boundary,
// it has the outside on its plus side and the inside on its minus side
plusOutside = minusChar.insideTouching();
splitters = new NodesSet();
splitters.addAll(minusChar.getInsideSplitters());
splitters.addAll(plusChar.getOutsideSplitters());
}
}
if (plusChar.touchInside()) {
// plusChar.insideTouching() corresponds to a subset of the cut sub-hyperplane
// known to have inside cells on its plus side, we want to check if parts
// of this subset do have outside cells on their minus side
final Characterization minusChar = new Characterization(node.getMinus(), plusChar.insideTouching());
if (minusChar.touchOutside()) {
// this part belongs to the boundary,
// it has the inside on its plus side and the outside on its minus side
plusInside = minusChar.outsideTouching();
if (splitters == null) {
splitters = new NodesSet();
}
splitters.addAll(minusChar.getOutsideSplitters());
splitters.addAll(plusChar.getInsideSplitters());
}
}
if (splitters != null) {
// the parent nodes are natural splitters for boundary sub-hyperplanes
for (BSPTree up = node.getParent(); up != null; up = up.getParent()) {
splitters.add(up);
}
}
// set the boundary attribute at non-leaf nodes
node.setAttribute(new BoundaryAttribute(plusOutside, plusInside, splitters));
}
/** {@inheritDoc} */
public void visitLeafNode(BSPTree node) {
}
}