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/* --------------------------------------------------------------------
* Copyright 2015 Gary W. Lucas.
*
* Licensed 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.
* ---------------------------------------------------------------------
*/
/*
* -----------------------------------------------------------------------
*
* Revision History:
* Date Name Description
* ------ --------- -------------------------------------------------
* 08/2015 G. Lucas Created
* 01/2017 G. Lucas Refactored to provide more generic functionality
*
* Notes:
*
* -----------------------------------------------------------------------
*/
package org.tinfour.common;
import java.util.BitSet;
import java.util.Iterator;
/**
* Provides descriptive data for a Triangulated Irregular Network (TIN).
*/
public class TriangleCount {
private int count;
private double sumArea;
private double sumArea2;
private double minArea = Double.POSITIVE_INFINITY;
private double maxArea = Double.NEGATIVE_INFINITY;
private double c; // compensator for Kahan summation for area
private double c2; // compensator for Kahan summation for area squared
private final GeometricOperations geoOp;
/**
* Create an instance for tabulating a survey of
* the triangles which may or may not be members of a TIN.
*/
public TriangleCount() {
geoOp = new GeometricOperations();
}
/**
* A constructor that performs a survey of the TIN to gather statistics
* about the triangles that comprise it.
*
* @param tin a valid instance of an incremental tin
*/
public TriangleCount(IIncrementalTin tin) {
geoOp = new GeometricOperations(tin.getThresholds());
if (tin.isBootstrapped()) {
int maxIndex = tin.getMaximumEdgeAllocationIndex();
int maxMapIndex = maxIndex + 2;
BitSet bitset = new BitSet(maxMapIndex);
Iterator iEdge = tin.getEdgeIterator();
while (iEdge.hasNext()) {
IQuadEdge e = iEdge.next();
if (e.getA() == null || e.getB() == null) {
setMarkBit(bitset, e);
setMarkBit(bitset, e.getDual());
continue;
}
this.countTriangleEdge(bitset, e);
this.countTriangleEdge(bitset, e.getDual());
}
}
}
/**
* Set the mark bit for an edge to 1.
*
* @param map an array at least as large as the largest edge index divided
* by 32
* @param edge a valid edge
*/
private void setMarkBit(BitSet bitset, final IQuadEdge edge) {
int index = edge.getIndex() ;
bitset.set(index);
}
/**
* Gets the edge mark bit.
*
* @param map an array at least as large as the largest edge index divided
* by 32
* @param edge a valid edge
* @return if the edge is marked, a non-zero value; otherwise, a zero.
*/
private boolean getMarkBit(BitSet bitset, final IQuadEdge edge) {
int index = edge.getIndex();
return bitset.get(index);
}
/**
* Process one side of an edge, develop a triangle if feasible.
*
* @param bitset a bitmap for tracking which edges have been added to
* triangles
* @param e the edge to inspect
*/
@SuppressWarnings("PMD.AvoidDeeplyNestedIfStmts")
private void countTriangleEdge(BitSet bitset, IQuadEdge e) {
if (!getMarkBit(bitset, e)) {
setMarkBit(bitset, e);
IQuadEdge f = e.getForward();
// ghost triangle, not tabulated
if (f.getB() != null) {
IQuadEdge r = e.getReverse();
// check to see that both neighbors are not marked.
if (!getMarkBit(bitset, f) && !getMarkBit(bitset, r)) {
setMarkBit(bitset, f);
setMarkBit(bitset, r);
tabulateTriangle(e.getA(), f.getA(), r.getA());
}
}
}
}
/**
* Compute area for the triangle specified by the vertex arguments and
* add it to the triangle count and area summations.
*
* @param vA the initial vertex, given in counterclockwise order
* @param vB the second vertex, given in counterclockwise order
* @param vC the third vertex, given in counterclockwise order
*/
public final void tabulateTriangle(Vertex vA, Vertex vB, Vertex vC) {
// compute the area and tabulate using the Kahan Summation Algorithm
count++;
double a, y, t;
a = geoOp.area(vA, vB, vC);
y = a - c;
t = sumArea + y;
c = (t - sumArea) - y;
sumArea = t;
y = a * a - c2;
t = sumArea2 + y;
c2 = (t - sumArea2) - y;
sumArea2 = t;
if (a < minArea) {
minArea = a;
}
if (a > maxArea) {
maxArea = a;
}
}
/**
* Get the number of triangles in the TIN.
*
* @return a integer value of 1 or more (zero if TIN is undefined).
*/
public int getCount() {
return count;
}
/**
* Gets the sum of the area of all triangles in the TIN.
*
* @return if the triangle count is greater than zero,
* a positive floating point value
*
*/
public double getAreaSum() {
return sumArea;
}
/**
* Get the mean area of the triangles in the TIN.
*
* @return if the triangle count is greater than zero,
* a positive floating point value
*/
public double getAreaMean() {
if (count == 0) {
return 0;
}
return sumArea / count;
}
/**
* Gets the standard deviation of the triangles in the TIN.
*
* @return if the triangle count is greater than one,
* a positive floating point value
*/
public double getAreaStandardDeviation() {
if (count < 2) {
return 0;
}
double n = count; // use double to avoid int overflow
double s = n * sumArea2 - sumArea * sumArea;
double t = n * (n - 1);
return Math.sqrt(s / t);
}
/**
* Gets the minimum area of the triangles in the TIN.
*
* @return if the triangle count is greater than zero,
* a positive floating point value
*/
public double getAreaMin() {
return minArea;
}
/**
* Gets the maximum area of the triangles in the TIN.
*
* @return if the triangle count is greater than zero,
* a positive floating point value
*/
public double getAreaMax() {
return maxArea;
}
}
