1.  auto buffer_geom = line_string->buffer(15);//buffer  //这个是x和y各扩大段15个单位

auto buffer_geom = line_string->buffer(15);//buffer  //这个是x和y各扩大段15米
获取buffer坐标
auto boundary = buffer_geom->getBoundary();
auto boundary_coords = boundary->getCoordinates();
int numVertices = boundary_coords->size();

double minX = boundary_coords->getAt(0).x;
double maxX = boundary_coords->getAt(0).x;
double minY = boundary_coords->getAt(0).y;
double maxY = boundary_coords->getAt(0).y;

for (int i = 1; i < numVertices; ++i) {
    auto coord = boundary_coords->getAt(i);
    double x = coord.x;
    double y = coord.y;

    if (x < minX) minX = x;
    if (x > maxX) maxX = x;
    if (y < minY) minY = y;
    if (y > maxY) maxY = y;
}

std::cout << "Min X: " << minX << ", Max X: " << maxX << std::endl;
std::cout << "Min Y: " << minY << ", Max Y: " << maxY << std::endl;

2.  这个才是沿着这条线段向两侧扩展15个单位

 auto line_string = geos::geom::GeometryFactory::getDefaultInstance()->createLineString(std::move(coordinate_seq));

                geos::operation::buffer::BufferParameters para;
                para.setJoinStyle(geos::operation::buffer::BufferParameters::JOIN_MITRE);
                para.setEndCapStyle(geos::operation::buffer::BufferParameters::CAP_FLAT);
                geos::operation::buffer::BufferOp bufferOp(line_string.get(), para);
                sp<geos::geom::Geometry> buffer_geom;
                buffer_geom.reset(bufferOp.getResultGeometry(15));