Class MinimumClearance
- java.lang.Object
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- org.locationtech.jts.precision.MinimumClearance
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public class MinimumClearance extends java.lang.Object
Computes the Minimum Clearance of aGeometry
.The Minimum Clearance is a measure of what magnitude of perturbation of the vertices of a geometry can be tolerated before the geometry becomes topologically invalid. The smaller the Minimum Clearance distance, the less vertex perturbation the geometry can tolerate before becoming invalid.
The concept was introduced by Thompson and Van Oosterom [TV06], based on earlier work by Milenkovic [Mi88].
The Minimum Clearance of a geometry G is defined to be the value r such that "the movement of all points by a distance of r in any direction will guarantee to leave the geometry valid" [TV06]. An equivalent constructive definition [Mi88] is that r is the largest value such:
- No two distinct vertices of G are closer than r
- No vertex of G is closer than r to an edge of G of which the vertex is not an endpoint
If G has only a single vertex (i.e. is a
Point
), the value of the minimum clearance isDouble.MAX_VALUE
.If G is a
Puntal
orLineal
geometry, then in fact no amount of perturbation will render the geometry invalid. In this case a Minimum Clearance is still computed based on the vertex and segment distances according to the constructive definition.It is possible for no Minimum Clearance to exist. For instance, a
MultiPoint
with all members identical has no Minimum Clearance (i.e. no amount of perturbation will cause the member points to become non-identical). Empty geometries also have no such distance. The lack of a meaningful MinimumClearance distance is detected and suitable values are returned bygetDistance()
andgetLine()
.The computation of Minimum Clearance utilizes the
STRtree.nearestNeighbour(ItemDistance)
method to provide good performance even for large inputs.An interesting note is that for the case of
MultiPoint
s, the computed Minimum Clearance line effectively determines the Nearest Neighbours in the collection.References
- [Mi88] Milenkovic, V. J., Verifiable implementations of geometric algorithms using finite precision arithmetic. in Artificial Intelligence, 377-401. 1988
- [TV06] Thompson, Rod and van Oosterom, Peter, Interchange of Spatial Data-Inhibiting Factors, Agile 2006, Visegrad, Hungary. 2006
- Author:
- Martin Davis
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Constructor Summary
Constructors Constructor Description MinimumClearance(Geometry geom)
Creates an object to compute the Minimum Clearance for the given Geometry
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description double
getDistance()
Gets the Minimum Clearance distance.static double
getDistance(Geometry g)
Computes the Minimum Clearance distance for the given Geometry.LineString
getLine()
Gets a LineString containing two points which are at the Minimum Clearance distance.static Geometry
getLine(Geometry g)
Gets a LineString containing two points which are at the Minimum Clearance distance for the given Geometry.
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Constructor Detail
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MinimumClearance
public MinimumClearance(Geometry geom)
Creates an object to compute the Minimum Clearance for the given Geometry- Parameters:
geom
- the input geometry
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Method Detail
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getDistance
public static double getDistance(Geometry g)
Computes the Minimum Clearance distance for the given Geometry.- Parameters:
g
- the input geometry- Returns:
- the Minimum Clearance distance
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getLine
public static Geometry getLine(Geometry g)
Gets a LineString containing two points which are at the Minimum Clearance distance for the given Geometry.- Parameters:
g
- the input geometry- Returns:
- the value of the minimum clearance distance or LINESTRING EMPTY if no Minimum Clearance distance exists
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getDistance
public double getDistance()
Gets the Minimum Clearance distance.If no distance exists (e.g. in the case of two identical points) Double.MAX_VALUE is returned.
- Returns:
- the value of the minimum clearance distance or Double.MAX_VALUE if no Minimum Clearance distance exists
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getLine
public LineString getLine()
Gets a LineString containing two points which are at the Minimum Clearance distance.If no distance could be found (e.g. in the case of two identical points) LINESTRING EMPTY is returned.
- Returns:
- the value of the minimum clearance distance or LINESTRING EMPTY if no Minimum Clearance distance exists
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