The base class for all geometric objects.
Because it is not clear at this time what semantics for spatial analysis methods involving
s would be useful,
s are not supported as arguments to binary predicates (other than
) or the
The spatial analysis methods will return the most specific class possible to represent the result. If the result is homogeneous, a
will be returned if the result contains a single element; otherwise, a
will be returned. If the result is heterogeneous a
will be returned.
Because it is not clear at this time what semantics for set-theoretic methods involving
GeometryCollections would be useful,
GeometryCollections are not supported as arguments to the set-theoretic methods.
Representation of Computed Geometries
The SFS states that the result of a set-theoretic method is the "point-set" result of the usual set-theoretic definition of the operation (SFS 126.96.36.199). However, there are sometimes many ways of representing a point set as a
The SFS does not specify an unambiguous representation of a given point set returned from a spatial analysis method. One goal of JTS is to make this specification precise and unambiguous. JTS will use a canonical form for
Geometrys returned from spatial analysis methods. The canonical form is a
Geometry which is simple and noded:
- Simple means that the Geometry returned will be simple according to the JTS definition of
- Noded applies only to overlays involving
LineStrings. It means that all intersection points on
LineStrings will be present as endpoints of
LineStrings in the result.
This definition implies that non-simple geometries which are arguments to spatial analysis methods must be subjected to a line-dissolve process to ensure that the results are simple.
Constructed Points And The Precision Model
The results computed by the set-theoretic methods may contain constructed points which are not present in the input
s. These new points arise from intersections between line segments in the edges of the input
s. In the general case it is not possible to represent constructed points exactly. This is due to the fact that the coordinates of an intersection point may contain twice as many bits of precision as the coordinates of the input line segments. In order to represent these constructed points explicitly, JTS must truncate them to fit the
Unfortunately, truncating coordinates moves them slightly. Line segments which would not be coincident in the exact result may become coincident in the truncated representation. This in turn leads to "topology collapses" -- situations where a computed element has a lower dimension than it would in the exact result.
When JTS detects topology collapses during the computation of spatial analysis methods, it will throw an exception. If possible the exception will report the location of the collapse.
#equals(Object) and #hashCode are not overridden, so that when two topologically equal Geometries are added to HashMaps and HashSets, they remain distinct. This behaviour is desired in many cases.