Linestring is generalized by an untuned (Ramer-)Douglas-Peucker
algorithm. Distance computation is still a naive implementation and can be further sped up if necessary
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DennisOSRM
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/*
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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 <stack>
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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., 512., 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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std::stack<PairOfPoints > recursionStack;
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double ComputeDistance(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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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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INFO("[" << recursionStack.size() << "] left: " << pair.first << ", right: " << 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(ComputeDistance(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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INFO("distance: " << maxDistance << ", recurse: " << (maxDistance > DouglasPeuckerThresholds[zoomLevel] ? "yes" : "no") << ", index: " << indexOfFarthestElement << ", threshold: " << DouglasPeuckerThresholds[zoomLevel] << ", z: " << zoomLevel);
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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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INFO("1 < " << indexOfFarthestElement << " - " << pair.first << "=" << (1 > indexOfFarthestElement - pair.first ? "yes" : "no"));
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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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unsigned necessaryCount = 0;
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BOOST_FOREACH(PointT & segment, inputVector) {
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if(segment.necessary)
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++necessaryCount;
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}
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INFO("[" << necessaryCount << "|" << inputVector.size() << "] points are necessary");
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}
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};
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#endif /* DOUGLASPEUCKER_H_ */
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@@ -58,18 +58,23 @@ private:
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public:
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inline void printEncodedString(const vector<SegmentInformation>& polyline, string &output) {
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vector<int> deltaNumbers(2*polyline.size());
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vector<int> deltaNumbers;
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output += "\"";
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if(!polyline.empty()) {
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deltaNumbers[0] = polyline[0].location.lat;
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deltaNumbers[1] = polyline[0].location.lon;
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_Coordinate lastCoordinate = polyline[0].location;
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deltaNumbers.push_back( lastCoordinate.lat );
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deltaNumbers.push_back( lastCoordinate.lon );
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for(unsigned i = 1; i < polyline.size(); ++i) {
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deltaNumbers[(2*i)] = (polyline[i].location.lat - polyline[i-1].location.lat);
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deltaNumbers[(2*i)+1] = (polyline[i].location.lon - polyline[i-1].location.lon);
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if(!polyline[i].necessary)
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continue;
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deltaNumbers.push_back(polyline[i].location.lat - lastCoordinate.lat);
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deltaNumbers.push_back(polyline[i].location.lon - lastCoordinate.lon);
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lastCoordinate = polyline[i].location;
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}
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encodeVectorSignedNumber(deltaNumbers, output);
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}
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output += "\"";
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}
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inline void printEncodedString(const vector<_Coordinate>& polyline, string &output) {
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@@ -109,6 +114,8 @@ public:
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output += "[";
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string tmp;
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for(unsigned i = 0; i < polyline.size(); i++) {
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if(!polyline[i].necessary)
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continue;
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convertInternalLatLonToString(polyline[i].location.lat, tmp);
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output += "[";
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output += tmp;
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