Class S2EdgeQuery

java.lang.Object

com.google.common.geometry.S2EdgeQuery

@GwtCompatible
public class S2EdgeQuery
extends Object

S2EdgeQuery is used to find edges or shapes that are crossed by an edge. If you need to query many edges, it is more efficient to declare a single S2EdgeQuery object and reuse it so that temporary storage does not need to be reallocated each time.

Here is an example showing how to index a set of polylines, and then find the polylines that are crossed by a given edge AB:

void test(Collection polylines, S2Point a0, S2Point a1) {
S2ShapeIndex index = new S2ShapeIndex();
for (int i = 0; i invalid input: '<' polylines.size(); ++i) {
index.add(polylines[i]);
}
S2EdgeQuery query = new S2EdgeQuery(index);
Mapinvalid input: '<'S2Shape, Edges> results = query.getCrossings(a, b);
for (Map.Entryinvalid input: '<'S2Shape, Edges> entry : results.entrySet()) {
S2Polyline polyline = (S2Polyline) entry.getKey();
for (Edges edges = entry.getValue(); !edges.isEmpty(); ) {
int edge = edges.getNext();
S2Point b0 = polyline.vertex(edge);
S2Point b1 = polyline.vertex(edge + 1);
// Guaranteed that each resulting edge is either a crossing or a degenerate crossing.
assertTrue(S2EdgeUtil.robustCrossing(a0, a1, b0, b1) >= 0);
}
}
}

Note that if you need to query many edges, it is more efficient to declare a single S2EdgeQuery object and reuse it so that temporary storage does not need to be reallocated each time.

This class is not thread-safe.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	S2EdgeQuery.Edges	An iterator over the sorted unique edge IDs of a shape that may intersect some query edge.
static final class	S2EdgeQuery.ShapeEdges	An Edges that contains all the edges of a shape with the given number of edges.

Constructor Summary

Constructors

Constructor	Description
S2EdgeQuery(S2ShapeIndex index)	Constructor from an S2ShapeIndex.

Method Summary

Modifier and Type	Method	Description
Map<S2Shape, S2EdgeQuery.Edges>	getCandidates(S2Point a, S2Point b)	Given a query edge AB, returns a map from the indexed shapes to a superset of the edges for each shape that intersect AB.
S2EdgeQuery.Edges	getCandidates(S2Point a, S2Point b, S2Shape shape)	Given a query edge AB and a shape shape, returns a superset of the edges of shape that intersect AB.
boolean	getCells(S2Point a, S2Point b, S2PaddedCell root, List<S2ShapeIndex.Cell> cells)	Convenience method for calling getCells(S2Point, R2Vector, S2Point, R2Vector, S2PaddedCell, List).
Map<S2Shape, S2EdgeQuery.Edges>	getCrossings(S2Point a, S2Point b)	Returns edges for each shape that either crosses AB or shares a vertex with AB.
S2EdgeQuery.Edges	getCrossings(S2Point a, S2Point b, S2Shape shape)	Returns edges from a given shape that either cross AB or share a vertex with AB.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

S2EdgeQuery

public S2EdgeQuery(S2ShapeIndex index)

Constructor from an S2ShapeIndex.

Method Details

getCrossings

public S2EdgeQuery.Edges getCrossings(S2Point a,
 S2Point b,
 S2Shape shape)

Returns edges from a given shape that either cross AB or share a vertex with AB.

getCrossings

public Map<S2Shape, S2EdgeQuery.Edges> getCrossings(S2Point a,
 S2Point b)

Returns edges for each shape that either crosses AB or shares a vertex with AB.

getCandidates

public S2EdgeQuery.Edges getCandidates(S2Point a,
 S2Point b,
 S2Shape shape)

Given a query edge AB and a shape shape, returns a superset of the edges of shape that intersect AB. Consider using S2EdgeQuery.ShapeEdges instead, if the shape has few enough edges.

getCandidates

public Map<S2Shape, S2EdgeQuery.Edges> getCandidates(S2Point a,
 S2Point b)

Given a query edge AB, returns a map from the indexed shapes to a superset of the edges for each shape that intersect AB. Consider using S2EdgeQuery.ShapeEdges instead, if there is just one indexed shape with few enough edges.

CAVEAT: This method may return shapes that have an empty set of candidate edges, i.e. result.get(shape).isEmpty() == true.

getCells

public boolean getCells(S2Point a,
 S2Point b,
 S2PaddedCell root,
 List<S2ShapeIndex.Cell> cells)

Convenience method for calling getCells(S2Point, R2Vector, S2Point, R2Vector, S2PaddedCell, List).