128 lines
5.3 KiB
C++
128 lines
5.3 KiB
C++
/*
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open source routing machine
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Copyright (C) Dennis Luxen, others 2010
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU AFFERO General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU Affero General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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or see http://www.gnu.org/licenses/agpl.txt.
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*/
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#ifndef DOUGLASPEUCKER_H_
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#define DOUGLASPEUCKER_H_
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#include <cfloat>
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#include "../DataStructures/SimpleStack.h"
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/*This class object computes the bitvector of indicating generalized input points
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* according to the (Ramer-)Douglas-Peucker algorithm.
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*
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* Input is vector of pairs. Each pair consists of the point information and a bit
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* indicating if the points is present in the generalization.
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* Note: points may also be pre-selected*/
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//These thresholds are more or less heuristically chosen.
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static double DouglasPeuckerThresholds[19] = { 10240000., 5120000., 2560000., 1280000., 640000., 320000., 160000., 80000., 40000., 20000., 10000., 5000., 2400., 1200., 200, 16, 6, 3., 1. };
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template<class PointT>
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class DouglasPeucker {
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private:
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typedef std::pair<std::size_t, std::size_t> PairOfPoints;
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//Stack to simulate the recursion
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SimpleStack<PairOfPoints > recursionStack;
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double ComputeDistanceOfPointToLine(const _Coordinate& inputPoint, const _Coordinate& source, const _Coordinate& target) {
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double r;
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const double x = (double)inputPoint.lat;
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const double y = (double)inputPoint.lon;
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const double a = (double)source.lat;
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const double b = (double)source.lon;
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const double c = (double)target.lat;
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const double d = (double)target.lon;
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double p,q,mX,nY;
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if(c != a) {
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const double m = (d-b)/(c-a); // slope
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// Projection of (x,y) on line joining (a,b) and (c,d)
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p = ((x + (m*y)) + (m*m*a - m*b))/(1 + m*m);
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q = b + m*(p - a);
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} else {
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p = c;
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q = y;
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}
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nY = (d*p - c*q)/(a*d - b*c);
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mX = (p - nY*a)/c;// These values are actually n/m+n and m/m+n , we neednot calculate the values of m an n as we are just interested in the ratio
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r = mX;
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if(r<=0){
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return ((b - y)*(b - y) + (a - x)*(a - x));
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}
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else if(r >= 1){
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return ((d - y)*(d - y) + (c - x)*(c - x));
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}
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// point lies in between
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return (p-x)*(p-x) + (q-y)*(q-y);
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}
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public:
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void Run(std::vector<PointT> & inputVector, const unsigned zoomLevel) {
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{
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assert(zoomLevel < 19);
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assert(1 < inputVector.size());
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std::size_t leftBorderOfRange = 0;
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std::size_t rightBorderOfRange = 1;
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//Sweep linerarily over array and identify those ranges that need to be checked
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recursionStack.hint(inputVector.size());
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do {
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assert(inputVector[leftBorderOfRange].necessary);
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assert(inputVector[inputVector.size()-1].necessary);
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if(inputVector[rightBorderOfRange].necessary) {
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recursionStack.push(std::make_pair(leftBorderOfRange, rightBorderOfRange));
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leftBorderOfRange = rightBorderOfRange;
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}
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++rightBorderOfRange;
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} while( rightBorderOfRange < inputVector.size());
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}
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while(!recursionStack.empty()) {
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//pop next element
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const PairOfPoints pair = recursionStack.top();
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recursionStack.pop();
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assert(inputVector[pair.first].necessary);
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assert(inputVector[pair.second].necessary);
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assert(pair.second < inputVector.size());
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assert(pair.first < pair.second);
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double maxDistance = -DBL_MAX;
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std::size_t indexOfFarthestElement = pair.second;
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//find index idx of element with maxDistance
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for(std::size_t i = pair.first+1; i < pair.second; ++i){
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double distance = std::fabs(ComputeDistanceOfPointToLine(inputVector[i].location, inputVector[pair.first].location, inputVector[pair.second].location));
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if(distance > DouglasPeuckerThresholds[zoomLevel] && distance > maxDistance) {
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indexOfFarthestElement = i;
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maxDistance = distance;
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}
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}
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if (maxDistance > DouglasPeuckerThresholds[zoomLevel]) {
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// mark idx as necessary
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inputVector[indexOfFarthestElement].necessary = true;
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if (1 < indexOfFarthestElement - pair.first) {
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recursionStack.push(std::make_pair(pair.first, indexOfFarthestElement) );
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}
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if (1 < pair.second - indexOfFarthestElement)
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recursionStack.push(std::make_pair(indexOfFarthestElement, pair.second) );
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}
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}
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}
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};
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#endif /* DOUGLASPEUCKER_H_ */
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