檢查是否linestring
的區段的起始點是在多邊形的內部或外部,以找出是否它正在進入或離開polygon
。簡單代碼示例:
// some demo polygon + line
Polygon polygon = new GeometryFactory().createPolygon(new Coordinate[]{new Coordinate(1,1), new Coordinate(6,1), new Coordinate(6,6), new Coordinate(1,6), new Coordinate(1,1)});
LineString line = new GeometryFactory().createLineString(new Coordinate[]{new Coordinate(0, 0), new Coordinate(5,5), new Coordinate(10,5)});
// check for intersection in the first place
if(line.intersects(polygon)){
System.out.println("line intersects polygon!");
// iterate over all segments of the linestring and check for intersections
for(int i = 1; i < line.getNumPoints(); i++){
// create line for current segment
LineString currentSegment = new GeometryFactory().createLineString(new Coordinate[]{line.getCoordinates()[i-1], line.getCoordinates()[i]});
// check if line is intersecting with ring
if(currentSegment.intersects(polygon)){
// segment is entering the ring if startpoint is outside the ring
if(!polygon.contains(currentSegment.getStartPoint())){
System.out.println("This segment is entering the polygon -> ");
System.out.println(currentSegment.toText());
// startpoint is inside the ring
}
if (polygon.contains(currentSegment.getStartPoint())) {
System.out.println("This segment is exiting the polygon -> ");
System.out.println(currentSegment.toText());
}
}
}
} else {
System.out.println("line is not intersecting the polygon!");
}
此代碼不涵蓋所有可能性。例如。如果單個線段多次與多邊形相交(輸入+退出),則此示例中未涉及。在這種情況下,只需計算交點的數量並在交點之間創建相應數量的線串。