...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Checks if a geometry is valid (in the OGC sense)
template<typename Geometry, typename Strategy> bool is_valid(Geometry const & geometry, validity_failure_type & failure, Strategy const & strategy)
Type |
Concept |
Name |
Description |
---|---|---|---|
Geometry const & |
Any type fulfilling a Geometry Concept |
geometry |
A model of the specified concept |
validity_failure_type & |
failure |
An enumeration value indicating that the geometry is valid or not, and if not valid indicating the reason why |
|
Strategy const & |
Any type fulfilling a Is_valid Strategy Concept |
strategy |
The strategy which will be used for is_valid calculations |
Returns true if the geometry is valid (in the OGC sense); furthermore, the following geometries are considered valid: multi-geometries with no elements, linear geometries containing spikes, areal geometries with duplicate (consecutive) points
Either
#include <boost/geometry.hpp>
Or
#include <boost/geometry/algorithms/is_valid.hpp>
The function is_valid is not defined by OGC.
Geometry |
Status |
---|---|
Point |
|
Segment |
|
Box |
|
Linestring |
|
Ring |
|
Polygon |
|
MultiPoint |
|
MultiLinestring |
|
MultiPolygon |
|
Variant |
|
Constant-time for points, segments, boxes and multi-points
Linear for linestrings and multi-linestrings
Linearithmic for rings
Currently, worst-case quadratic for polygons and multi-polygons
Checks whether a geometry is valid and, if not valid, checks if it could be fixed by bg::correct; if so bg::correct is called on the geometry
#include <iostream> #include <boost/geometry.hpp> #include <boost/geometry/geometries/point_xy.hpp> #include <boost/geometry/geometries/polygon.hpp> int main() { typedef boost::geometry::model::d2::point_xy<double> point_type; typedef boost::geometry::model::polygon<point_type> polygon_type; polygon_type poly; boost::geometry::read_wkt("POLYGON((0 0,0 10,10 10,10 0),(0 0,9 2,9 1,0 0),(0 0,2 9,1 9,0 0))", poly); std::cout << "original geometry: " << boost::geometry::dsv(poly) << std::endl; boost::geometry::validity_failure_type failure; bool valid = boost::geometry::is_valid(poly, failure); // if the invalidity is only due to lack of closing points and/or wrongly oriented rings, then bg::correct can fix it bool could_be_fixed = (failure == boost::geometry::failure_not_closed || boost::geometry::failure_wrong_orientation); std::cout << "is valid? " << (valid ? "yes" : "no") << std::endl; if (! valid) { std::cout << "can boost::geometry::correct remedy invalidity? " << (could_be_fixed ? "possibly yes" : "no") << std::endl; if (could_be_fixed) { boost::geometry::correct(poly); std::cout << "after correction: " << (boost::geometry::is_valid(poly) ? "valid" : "still invalid") << std::endl; std::cout << "corrected geometry: " << boost::geometry::dsv(poly) << std::endl; } } return 0; }
Output:
original geometry: (((0, 0), (0, 10), (10, 10), (10, 0)), ((0, 0), (9, 2), (9, 1), (0, 0)), ((0, 0), (2, 9), (1, 9), (0, 0))) is valid? no can boost::geometry::correct remedy invalidity? possibly yes after correction: valid corrected geometry: (((0, 0), (0, 10), (10, 10), (10, 0), (0, 0)), ((0, 0), (9, 1), (9, 2), (0, 0)), ((0, 0), (2, 9), (1, 9), (0, 0)))