diff --git a/Algorithms/DouglasPeucker.h b/Algorithms/DouglasPeucker.h index 215d2a1ce..e0feb45d5 100644 --- a/Algorithms/DouglasPeucker.h +++ b/Algorithms/DouglasPeucker.h @@ -29,15 +29,15 @@ or see http://www.gnu.org/licenses/agpl.txt. #include "../DataStructures/Coordinate.h" /*This class object computes the bitvector of indicating generalized input points - * according to the (Ramer-)Douglas-Peucker algorithm. Runtime n\log n calls to fastDistance + * according to the (Ramer-)Douglas-Peucker algorithm. * * Input is vector of pairs. Each pair consists of the point information and a bit * indicating if the points is present in the generalization. * Note: points may also be pre-selected*/ //These thresholds are more or less heuristically chosen. -// 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 -static double DouglasPeuckerThresholds[19] = { 32000000, 16240000, 80240000, 40240000, 20000000, 10000000, 500000, 240000, 120000, 60000, 30000, 19000, 5000, 2000, 200, 16, 6, 3, 3 }; +// 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 +static double DouglasPeuckerThresholds[19] = { 32000000., 16240000., 80240000., 40240000., 20000000., 10000000., 500000., 240000., 120000., 60000., 30000., 19000., 5000., 2000., 200, 16, 6, 3. , 3. }; template class DouglasPeucker { @@ -45,27 +45,58 @@ private: typedef std::pair PairOfPoints; //Stack to simulate the recursion std::stack recursionStack; + + double ComputeDistanceOfPointToLine(const _Coordinate& inputPoint, const _Coordinate& source, const _Coordinate& target) const { + double r = 0.; + const double x = static_cast(inputPoint.lat); + const double y = static_cast(inputPoint.lon); + const double a = static_cast(source.lat); + const double b = static_cast(source.lon); + const double c = static_cast(target.lat); + const double d = static_cast(target.lon); + double p,q,mX,nY; + if(fabs(a - c) <= FLT_EPSILON) { + const double m = (d-b)/(c-a); // slope + // Projection of (x,y) on line joining (a,b) and (c,d) + p = ((x + (m*y)) + (m*m*a - m*b))/(1 + m*m); + q = b + m*(p - a); + } else { + p = c; + q = y; + } + nY = (d*p - c*q)/(a*d - b*c); + 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 + r = std::isnan(mX) ? 0. : mX; + if(r<=0.){ + return ((b - y)*(b - y) + (a - x)*(a - x)); + } + else if(r >= 1.){ + return ((d - y)*(d - y) + (c - x)*(c - x)); + + } + // point lies in between + return (p-x)*(p-x) + (q-y)*(q-y); + } + public: void Run(std::vector & inputVector, const unsigned zoomLevel) { - const unsigned sizeOfInputVector = inputVector.size(); { assert(zoomLevel < 19); assert(1 < inputVector.size()); std::size_t leftBorderOfRange = 0; std::size_t rightBorderOfRange = 1; - //Sweep linerarily over array and identify those ranges that need to be checked - //decision points have been previously marked +// recursionStack.hint(inputVector.size()); do { assert(inputVector[leftBorderOfRange].necessary); - assert(inputVector[inputVector.back()].necessary); + assert(inputVector[inputVector.size()-1].necessary); if(inputVector[rightBorderOfRange].necessary) { recursionStack.push(std::make_pair(leftBorderOfRange, rightBorderOfRange)); leftBorderOfRange = rightBorderOfRange; } ++rightBorderOfRange; - } while( rightBorderOfRange < sizeOfInputVector); + } while( rightBorderOfRange < inputVector.size()); } while(!recursionStack.empty()) { //pop next element @@ -73,13 +104,13 @@ public: recursionStack.pop(); assert(inputVector[pair.first].necessary); assert(inputVector[pair.second].necessary); - assert(pair.second < sizeOfInputVector); + assert(pair.second < inputVector.size()); assert(pair.first < pair.second); - int maxDistance = -INT_MIN; + double maxDistance = -DBL_MAX; std::size_t indexOfFarthestElement = pair.second; //find index idx of element with maxDistance for(std::size_t i = pair.first+1; i < pair.second; ++i){ - const int distance = fastDistance(inputVector[i].location, inputVector[pair.first].location, inputVector[pair.second].location); + const double distance = std::fabs(ComputeDistanceOfPointToLine(inputVector[i].location, inputVector[pair.first].location, inputVector[pair.second].location)); if(distance > DouglasPeuckerThresholds[zoomLevel] && distance > maxDistance) { indexOfFarthestElement = i; maxDistance = distance; @@ -96,34 +127,6 @@ public: } } } - - /** - * This distance computation does integer arithmetic only and is about twice as fast as - * the other distance function. It is an approximation only, but works more or less ok. - */ - template - double fastDistance(const CoordT& point, const CoordT& segA, const CoordT& segB) { - int p2x = (segB.lon - segA.lat); - int p2y = (segB.lon - segA.lat); - int something = p2x*p2x + p2y*p2y; - int u = ((point.lon - segA.lon) * p2x + (point.lat - segA.lat) * p2y) / something; - - if (u > 1) - u = 1; - else if (u < 0) - u = 0; - - int x = segA.lon + u * p2x; - int y = segA.lat + u * p2y; - - int dx = x - point.lon; - int dy = y - point.lat; - - int dist = (dx*dx + dy*dy); - - return dist; - } - }; #endif /* DOUGLASPEUCKER_H_ */