public class MinimumClearance extends Object
Geometry
.
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:
If G has only a single vertex (i.e. is a
Point
), the value of the minimum clearance
is Double.MAX_VALUE
.
If G is a Puntal
or Lineal
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 nonidentical).
Empty geometries also have no such distance.
The lack of a meaningful MinimumClearance distance is detected
and suitable values are returned by
getDistance()
and getLine()
.
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.
Constructor and Description 

MinimumClearance(Geometry geom)
Creates an object to compute the Minimum Clearance
for the given Geometry

Modifier and Type  Method and 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.

public MinimumClearance(Geometry geom)
geom
 the input geometrypublic static double getDistance(Geometry g)
g
 the input geometrypublic static Geometry getLine(Geometry g)
g
 the input geometrypublic double getDistance()
If no distance exists (e.g. in the case of two identical points) Double.MAX_VALUE is returned.
public LineString getLine()
If no distance could be found (e.g. in the case of two identical points) LINESTRING EMPTY is returned.
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