基于C++、GDAL、OpenCV的矢量数据骨架线提取算法
CGAL已经实现了该功能，但由于CGAL依赖于Boost库，编译后过大，因此本文所采用的这套方式实现骨架线提取功能。
效果：
思路：
1、将导入shp按照要素逐一拆分成新的shp
2、将所有拆分后的shp分别转栅格，利用OpenCV提取骨架线
3、将所有骨架线转为shp，并合并输出
详细代码如下：
调用
basePolygonAlgorithm::SkeletonExtractor extract2;
extract2.polygon2Skelton("originFile.shp", "outputFile.shp");
.h
#include "opencv2/core/core.hpp"
#include "opencv2/opencv.hpp"
#include"opencv2/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "ogrsf_frmts.h"
#include "gdal_priv.h"
#include "ogr_geometry.h"
#include "ogr_attrind.h"
#include "ogr_srs_api.h"
//提取骨架线
class SkeletonExtractor
{
public:
SkeletonExtractor();
void polygon2Skelton(string src_path, string dst_path);//src_path待提取数据 dst_path：提取后数据
;
private:
cv::Mat thinning(cv::Mat img);//Mat骨架线提取
cv::Mat readRasterData(GDALDataset* pDstDataset);//pDstDataset转Mat
void polygon2subPolygon(const string& src_path, int* featureNum, double adfGeoTransform[6]);
void subPolygon2skelton(const string& dst_path, const int& featureNum, double adfGeoTransform[6]);
void mergeShp(vector<string>vecSrcFiles, string pszDstFile);
void writeShp(string dst_path, cv::Mat skel, double adfGeoTransform[], OGRSpatialReference* oSRS);
};
.cpp
SkeletonExtractor::SkeletonExtractor()
{
}
void SkeletonExtractor::polygon2Skelton(string src_path, string dst_path)
{
int featureNum = 0;
double adfGeoTransform[6];
polygon2subPolygon(src_path, &featureNum, adfGeoTransform);
subPolygon2skelton(dst_path, featureNum, adfGeoTransform);
return;
}
cv::Mat SkeletonExtractor::thinning(cv::Mat img)
{
cv::Mat skel(img.size(), CV_8UC1, cv::Scalar(0));
cv::Mat temp(img.size(), CV_8UC1);
cv::Mat element = cv::getStructuringElement(cv::MORPH_CROSS, cv::Size(3, 3));
bool done;
do
{
cv::morphologyEx(img, temp, cv::MORPH_OPEN, element);
cv::bitwise_not(temp, temp);
cv::bitwise_and(img, temp, temp);
cv::bitwise_or(skel, temp, skel);
cv::erode(img, img, element);
double maxVal = 0;
cv::minMaxLoc(img, nullptr, &maxVal);
done = (maxVal == 0);
} while (!done);
img.release();
temp.release();
return skel;
}
cv::Mat SkeletonExtractor::readRasterData(GDALDataset* pDstDataset)
{
// Read the first band of the raster dataset
GDALRasterBand* pBand = pDstDataset->GetRasterBand(1);
// Allocate memory for the raster data
int nXSize = pBand->GetXSize();
int nYSize = pBand->GetYSize();
GByte* pData = new GByte[nXSize * nYSize];
// Read the raster data
pBand->RasterIO(GF_Read, 0, 0, nXSize, nYSize, pData, nXSize, nYSize, GDT_Byte, 0, 0);
//转化为Mat
cv::Mat _Mymat(nYSize, nXSize, CV_8UC1);
for (int i = 0; i < nXSize; i++)
{
for (int j = 0; j < nYSize; j++)
{
_Mymat.at<uchar>(j, i) = (uchar)pData[j * nXSize + i];
}
}
// 执行骨架化
cv::Mat skel;
skel = thinning(_Mymat);
// 定义结构元素（如3x3的矩形）
int morph_size = 1;
cv::Mat element = cv::getStructuringElement(cv::MORPH_RECT,
cv::Size(2 * morph_size + 1, 2 * morph_size + 1),
cv::Point(morph_size, morph_size));
// 膨胀操作
cv::dilate(skel, skel, element);
// 腐蚀操作
cv::erode(skel, skel, element);
delete[] pData;
return skel;
}
void SkeletonExtractor::polygon2subPolygon(const string& src_path, int* featureNum, double adfGeoTransform[6])
{
// Register GDAL drivers
GDALAllRegister();
OGRRegisterAll();
// NULL, NULL, NULL));
GDALDataset* pSrcDataset = (GDALDataset*)GDALOpenEx(src_path.c_str(), GDAL_OF_VECTOR, NULL, NULL, NULL);
// The one layer.
OGRLayer* pSrcLayer = pSrcDataset->GetLayer(0);
OGRSpatialReference* oSRS = NULL;
oSRS = new OGRSpatialReference;
oSRS = pSrcLayer->GetSpatialRef();
*featureNum = pSrcLayer->GetFeatureCount();
pSrcDataset->GetGeoTransform(adfGeoTransform);
for (int i = 0; i < *featureNum; i++) {
// 获取要素
OGRFeature* pSrcFeature = pSrcLayer->GetFeature(i);
// 创建新的GDALDataset和图层
char outputFilename[256];
sprintf(outputFilename, "temp_%d.shp", i);
GDALDriver* pDriver = GetGDALDriverManager()->GetDriverByName("ESRI Shapefile");
GDALDataset* temp_pDstDataset = pDriver->Create(outputFilename, 0, 0, 0, GDT_Unknown, NULL);
OGRLayer* pDstLayer = temp_pDstDataset->CreateLayer(pSrcLayer->GetName(), oSRS, pSrcLayer->GetGeomType(), NULL);
// 复制要素到新的图层中
OGRFeature* pDstFeature = pSrcFeature->Clone();
pDstLayer->CreateFeature(pDstFeature);
OGRFeature::DestroyFeature(pDstFeature);
GDALFlushCache(temp_pDstDataset);
// 释放资源
GDALClose(temp_pDstDataset);
OGRFeature::DestroyFeature(pSrcFeature);
}
GDALClose(pSrcDataset);
}
void SkeletonExtractor::mergeShp(vector<string> vecSrcFiles, string pszDstFile)
{
GDALAllRegister();
// 获取Shapefile驱动
GDALDriver* poDriver = GetGDALDriverManager()->GetDriverByName("ESRI Shapefile");
if (poDriver == nullptr) {
cerr << "ESRI Shapefile driver not available." << endl;
return;
}
// 创建目标shapefile
GDALDataset* poDstDS = poDriver->Create(pszDstFile.c_str(), 0, 0, 0, GDT_Unknown, nullptr);
if (poDstDS == nullptr) {
cerr << "Creation of output file failed." << endl;
return;
}
OGRLayer* poDstLayer = nullptr;
// 遍历所有源shapefile
for (const auto& srcFile : vecSrcFiles) {
GDALDataset* poSrcDS = static_cast<GDALDataset*>(GDALOpenEx(srcFile.c_str(), GDAL_OF_VECTOR, nullptr, nullptr, nullptr));
if (poSrcDS == nullptr) {
cerr << "Open failed: " << srcFile << endl;
continue;
}
OGRLayer* poSrcLayer = poSrcDS->GetLayer(0);
if (poSrcLayer == nullptr) {
cerr << "Failed to get layer from source file: " << srcFile << endl;
GDALClose(poSrcDS);
continue;
}
// 如果目标图层不存在，则根据源图层创建一个
if (poDstLayer == nullptr) {
poDstLayer = poDstDS->CreateLayer(poSrcLayer->GetName(), poSrcLayer->GetSpatialRef(), poSrcLayer->GetGeomType(), nullptr);
if (poDstLayer == nullptr) {
cerr << "Failed to create destination layer." << endl;
GDALClose(poSrcDS);
GDALClose(poDstDS);
return;
}
// 复制属性表结构
OGRFeatureDefn* poSrcFDefn = poSrcLayer->GetLayerDefn();
for (int i = 0; i < poSrcFDefn->GetFieldCount(); ++i) {
poDstLayer->CreateField(poSrcFDefn->GetFieldDefn(i));
}
}
// 复制要素
OGRFeature* poFeature;
poSrcLayer->ResetReading();
while ((poFeature = poSrcLayer->GetNextFeature()) != nullptr) {
OGRFeature* poDstFeature = OGRFeature::CreateFeature(poDstLayer->GetLayerDefn());
poDstFeature->SetFrom(poFeature);
poDstFeature->SetGeometry(poFeature->GetGeometryRef());
if (poDstLayer->CreateFeature(poDstFeature) != OGRERR_NONE) {
cerr << "Failed to create feature in destination shapefile." << endl;
OGRFeature::DestroyFeature(poFeature);
OGRFeature::DestroyFeature(poDstFeature);
GDALClose(poSrcDS);
GDALClose(poDstDS);
return;
}
OGRFeature::DestroyFeature(poFeature);
OGRFeature::DestroyFeature(poDstFeature);
}
GDALClose(poSrcDS);
}
GDALClose(poDstDS);
}
void SkeletonExtractor::writeShp(string dst_path, cv::Mat skel, double adfGeoTransform[], OGRSpatialReference* oSRS)
{
GDALAllRegister();
OGRRegisterAll();
GDALDriver* poDriver = GetGDALDriverManager()->GetDriverByName("ESRI Shapefile");
GDALDataset* poDS = poDriver->Create(dst_path.c_str(), 0, 0, 0, GDT_Unknown, NULL);
OGRLayer* poLayer = poDS->CreateLayer("layer", oSRS, wkbUnknown, NULL);
std::vector<cv::Vec4i> hierarchy;
std::vector<std::vector<cv::Point>> contours;
cv::findContours(skel, contours, hierarchy, cv::RETR_EXTERNAL, cv::CHAIN_APPROX_NONE);
OGRMultiLineString multiLineString;
OGRFeature* poFeature = OGRFeature::CreateFeature(poLayer->GetLayerDefn());
for (int i = 0; i < contours.size(); i++)
{
OGRLineString lineString;
for (int j = 0; j < contours[i].size(); j++)
{
double x = adfGeoTransform[0] + contours[i][j].x * adfGeoTransform[1] + contours[i][j].y * adfGeoTransform[2];
double y = adfGeoTransform[3] + contours[i][j].x * adfGeoTransform[4] + contours[i][j].y * adfGeoTransform[5];
lineString.addPoint(x, y);
}
multiLineString.addGeometry(&lineString);
}
poFeature->SetGeometry(&multiLineString);
skelton_result = poFeature->GetGeometryRef()->clone();//clone将skelton_result复制到一个新的 OGRGeometry 对象中，防止因poFeature释放而变成空
poLayer->CreateFeature(poFeature);
OGRFeature::DestroyFeature(poFeature);
GDALClose(poDS);
hierarchy.clear();
contours.clear();
}
void SkeletonExtractor::subPolygon2skelton(const string& dst_path, const int& featureNum, double adfGeoTransform[6])
{
GDALAllRegister();
OGRRegisterAll();
//栅格参数设置
char** argv = NULL;
//nodata
argv = CSLAddString(argv, "-a_nodata");
argv = CSLAddString(argv, "-9999");
//初始值
argv = CSLAddString(argv, "-init");
argv = CSLAddString(argv, "0");
//分辨率
argv = CSLAddString(argv, "-ts");
argv = CSLAddString(argv, "1024");
argv = CSLAddString(argv, "1024");
//存储类型
argv = CSLAddString(argv, "-ot");
argv = CSLAddString(argv, "Byte");
GDALRasterizeOptions* pOptions = GDALRasterizeOptionsNew(argv, NULL);
OGRSpatialReference* oSRS = NULL;
vector<string>filePaths;
for (int i = 0; i < featureNum; i++) {
//重新打开新的SHP文件
char outputFilename[256];
sprintf(outputFilename, "temp_%d.shp", i);
GDALDataset* pNewDS = (GDALDataset*)GDALOpenEx(outputFilename, GDAL_OF_VECTOR, NULL, NULL, NULL);
OGRLayer* pNewLayer = pNewDS->GetLayer(0);
oSRS = new OGRSpatialReference;
oSRS = pNewLayer->GetSpatialRef();
//获取转换6参数
int pbUsageError = FALSE;
GDALDataset* pImageDataset = static_cast<GDALDataset*>(GDALRasterize("output.tif", NULL, pNewDS, pOptions, &pbUsageError));
double adfGeoTransform[6];
pImageDataset->GetGeoTransform(adfGeoTransform);
//提取骨架线
cv::Mat skel = readRasterData(pImageDataset);
//写入结果
outputFilename[256];
sprintf(outputFilename, "res_%d.shp", i);
writeShp(outputFilename, skel, adfGeoTransform, oSRS);
filePaths.push_back(outputFilename);
GDALClose(pNewDS);
GDALClose(pImageDataset);
skel.release();
}
// Close the datasets
GDALRasterizeOptionsFree(pOptions);
//合并shp
mergeShp(filePaths, dst_path);
//删除临时文件
for (int i = 0; i < featureNum; i++) {
char tempFile[256];
char resFile[256];
sprintf(tempFile, "temp_%d.shp", i);
std::remove(tempFile);
sprintf(tempFile, "temp_%d.shx", i);
std::remove(tempFile);
sprintf(tempFile, "temp_%d.dbf", i);
std::remove(tempFile);
sprintf(tempFile, "temp_%d.prj", i);
std::remove(tempFile);
sprintf(resFile, "res_%d.shp", i);
std::remove(resFile);
sprintf(resFile, "res_%d.shx", i);
std::remove(resFile);
sprintf(resFile, "res_%d.dbf", i);
std::remove(resFile);
sprintf(resFile, "res_%d.prj", i);
std::remove(resFile);
}
std::remove("output.tif");
return;
}