c++ 扫描线填充算法实现，对 DEM 数据进行置平

ScanlineFilling.h

#include 
#include 
class ScanlineFilling
{
	public:
		class Edge {
		public:
			int x1, y1, x2, y2, dx, dy;
			Edge(int x1, int y1, int x2, int y2);
		};

	private:
		std::vector<Edge> edgeTable;
		int  getYmin();
		int  getYmax();
		bool  isActive(Edge edge, int currentY);
		void  updateActiveEdges(std::vector<Edge>& activeEdges, int y);
		void  findIntersections(std::vector<int>& intersections, std::vector <Edge> activeEdges, int currentY);
	public:
		// 多边形填充
		// 参数：matrix:		要填充的二维数组，
		//		x,y:		数组的行列，
		//		position:	多边形的坐标[x,y]，
		//		len:		多边形坐标的个数(从起点到终点的个数，其中起点==终点)，
		//		fillValue:	填充的值
		void fill(int** matrix, int x, int y, int** position, int len, int fillValue);
};

ScanlineFilling.cpp

#include "ScanlineFilling.h"
#include 
#include 
#include 

using namespace std;

ScanlineFilling::Edge::Edge(int x1, int y1, int x2, int y2) {
	this->x1 = x1;
	this->y1 = y1;
	this->x2 = x2;
	this->y2 = y2;
	this->dx = x2 - x1;
	this->dy = y2 - y1;
}

int ScanlineFilling::getYmin() {
	int yMin = edgeTable.front().y1;
	for (Edge edge : edgeTable) {
		if (edge.y1 < yMin)
			yMin = edge.y1;
	}
	return yMin;
}

int ScanlineFilling::getYmax() {
	int yMax = edgeTable.front().y1;
	for (Edge edge : edgeTable) {
		if (edge.y1 > yMax)
			yMax = edge.y1;
	}
	return yMax;
}

bool ScanlineFilling::isActive(Edge edge, int currentY) {
	return edge.y1 < currentY && currentY <= edge.y2 || edge.y1 >= currentY && currentY > edge.y2;
}

void ScanlineFilling::updateActiveEdges(std::vector<Edge>& activeEdges, int y) {
	for (Edge edge : edgeTable) {
		if (isActive(edge, y)) {
			activeEdges.push_back(edge);
		}
	}
}

void ScanlineFilling::findIntersections(std::vector<int>& intersections, std::vector<Edge> activeEdges, int currentY) {
	for (Edge edge : activeEdges) {
		int x = edge.x1 + ((currentY - edge.y1) * (edge.dx)) / (edge.dy);
		intersections.push_back(x);
	}
}

// 多边形填充
// 参数：matrix:		要填充的二维数组，
//		x,y:		数组的行列，
//		position:	多边形的坐标[x,y]，
//		len:		多边形坐标的个数(从起点到终点的个数，其中起点==终点)，
//		fillValue:	填充的值
void ScanlineFilling::fill(int** matrix, int x, int y, int** position, int len,int fillValue) {
	vector<Edge> activeEdges;
	vector<int> intersections;
	int firstX, firstY;
	edgeTable.clear();
	// 获取要填充的多边形的边
	for (int i = 0; i < len; i++) {
		if (i == 0) {
			firstX = position[i][0];
			firstY = position[i][1];
			continue;
		}
		edgeTable.push_back(*(new Edge(firstX, firstY, position[i][0], position[i][1])));
		firstX = position[i][0];
		firstY = position[i][1];
	}
	int yMin = getYmin();
	int yMax = getYmax();
	for (int y = yMin; y < yMax; y++) {
		activeEdges.clear();
		intersections.clear();
		updateActiveEdges(activeEdges, y);
		findIntersections(intersections, activeEdges, y);
		// 升序
		sort(intersections.begin(),intersections.end());
		for (int i = 0; i < intersections.size(); i += 2) {
			int x1 = intersections[i];
			if ((i + 1) >= intersections.size()) {
				break;
			}
			int x2 = intersections[i + 1];
			for (int k = x1; k < x2; k++) {
				matrix[k][y] = fillValue;
			}
		}
	}
}

二维矩阵填充测试：

int main() {

	int** matrix = new int* [10];
	for (int i = 0; i < 10; i++) {
		matrix[i] = new int[10];
		for (int j = 0; j < 10; j++) {
			matrix[i][j] = 0;
		}
	}

	int** position = new int* [4];
	position[0] = new int[2];
	position[1] = new int[2];
	position[2] = new int[2];
	position[3] = new int[2];
	// 起点
	position[0][0] = 2;
	position[0][1] = 2;
	// 中间点
	position[1][0] = 2;
	position[1][1] = 8;
	position[2][0] = 8;
	position[2][1] = 7;
	// 终点
	position[3][0] = 2;
	position[3][1] = 2;
	ScanlineFilling* sc = new ScanlineFilling();
	sc->fill(matrix, 10, 10, position, 4, 1);
	// 打印填充结果
	for (int i = 0; i < 10; i++) {
		for (int j = 0; j < 10; j++) {
			cout << matrix[i][j] << "   ";
		}
		cout << endl;
	}
	return 0;
}

对 DEM 数据进行置平

ScanlineFilling* sc = new ScanlineFilling();
// greyValue： dem 高程值二维矩阵
// X,Y:		   dem 高程值二维矩阵在 x(lat),y(lon)方向上的像素个数
// position:   要填充的多边形的坐标（第一个点和最后一个点相同）,
//			   用 shp 文件置平，经纬度要转换为 dem 高程值的索引位置
// pointCount: 多边形坐标个数， position.length
// minGreyValue: 要填充的高程值
sc->fill(greyValue, X, Y, position, pointCount, minGreyValue);

填充结果：