c – 如何在GEOS中制作矩形？
作者：互联网
如何使用GEOS库的C API制作矩形？
解决方法:
以下实现在GEOS中完成了工作.
//Compile with: g++ code.cpp -lgeos
//Updated: 2019-03-31
#include <geos/geom/PrecisionModel.h>
#include <geos/geom/Polygon.h>
#include <geos/geom/LinearRing.h>
#include <geos/geom/CoordinateSequenceFactory.h>
#include <geos/geom/Geometry.h>
#include <geos/geom/GeometryFactory.h>
#include <iostream>
#include <memory>
geos::geom::Polygon* MakeBox(double xmin, double ymin, double xmax, double ymax){
std::unique_ptr<geos::geom::PrecisionModel> pm(new geos::geom::PrecisionModel());
geos::geom::GeometryFactory::unique_ptr factory = geos::geom::GeometryFactory::create(pm.get(), -1);
geos::geom::CoordinateSequence *temp = factory->getCoordinateSequenceFactory()->create((std::size_t) 0, 0);
temp->add(geos::geom::Coordinate(xmin, ymin));
temp->add(geos::geom::Coordinate(xmin, ymax));
temp->add(geos::geom::Coordinate(xmax, ymax));
temp->add(geos::geom::Coordinate(xmax, ymin));
//Must close the linear ring or we will get an error:
//"Points of LinearRing do not form a closed linestring"
temp->add(geos::geom::Coordinate(xmin, ymin));
geos::geom::LinearRing *shell=factory->createLinearRing(temp);
//NULL in this case could instead be a collection of one or more holes
//in the interior of the polygon
return factory->createPolygon(shell,NULL);
}
int main(){
geos::geom::Polygon* box = MakeBox(0,0,10,10);
std::cout<<box->getArea()<<std::endl;
delete box; //Important to avoid memory leaks
}
作为参考,您也可以使用boost::polygon库完成此操作,如下所示.
//Compile with: g++ code.cpp
#include <boost/polygon/polygon.hpp>
#include <iostream>
namespace gtl = boost::polygon;
typedef gtl::polygon_data<float> Polygon;
Polygon MakeBox(float xmin, float ymin, float xmax, float ymax){
typedef gtl::polygon_traits<Polygon>::point_type Point;
Point pts[] = {
gtl::construct<Point>(xmin, ymin),
gtl::construct<Point>(xmin, ymax),
gtl::construct<Point>(xmax, ymax),
gtl::construct<Point>(xmax, ymin)
};
Polygon poly;
gtl::set_points(poly, pts, pts+4);
return poly;
}
int main(){
Polygon box = MakeBox(0,0,10,10);
std::cout<<gtl::area(box)<<std::endl;
}
并且还有Clipper.请注意,Clipper不能使用浮点坐标.
#include "clipper_cpp/clipper.hpp"
#include <iostream>
ClipperLib::Paths MakeBox(int xmin, int ymin, int xmax, int ymax){
ClipperLib::Paths box(1);
//Note that we run the path in the reverse direction to previous examples in
//order to maintain positive area
box[0] << ClipperLib::IntPoint(xmin,ymin) << ClipperLib::IntPoint(xmax,ymin)
<< ClipperLib::IntPoint(xmax,ymax) << ClipperLib::IntPoint(xmin,ymax);
return box;
}
int main(){
ClipperLib::Paths box = MakeBox(0,0,10,10);
std::cout<<ClipperLib::Area(box[0])<<std::endl;
}