Class GraphOptions
This class is only needed by S2Builder::Layer implementations. A layer is
responsible for assembling an S2Builder::Graph of snapped edges into the
desired output format (e.g., an S2Polygon). The GraphOptions class allows
each Layer type to specify requirements on its input graph: for example, if
Constructors
| Name | Description |
this
(edge_type, degenerate_edges, duplicate_edges, sibling_pairs)
|
All S2Builder::Layer subtypes should specify GraphOptions explicitly
using this constructor, rather than relying on default values.
|
this
()
|
The default options specify that all edges should be kept, since this
produces the least surprising output and makes it easier to diagnose the
problem when an option is left unspecified.
|
Methods
| Name | Description |
allowVertexFiltering
()
|
This is a specialized option that is only needed by clients want to work
with the graphs for multiple layers at the same time (e.g., in order to
check whether the same edge is present in two different graphs). [Note
that if you need to do this, usually it is easier just to build a single
graph with suitable edge labels.]
|
edgeType
()
|
Specifies whether the S2Builder input edges should be treated as
undirected. If true, then all input edges are duplicated into pairs
consisting of an edge and a sibling (reverse) edge. The layer
implementation is responsible for ensuring that exactly one edge from
each pair is used in the output, i.e. *only half* of the graph edges will
be used. (Note that some values of the sibling_pairs() option
automatically take care of this issue by removing half of the edges and
changing edge_type() to DIRECTED.)
|
Enums
| Name | Description |
DegenerateEdges
|
Controls how degenerate edges (i.e., an edge from a vertex to itself) are
handled. Such edges may be present in the input, or they may be created
when both endpoints of an edge are snapped to the same output vertex.
The options available are:
|
DuplicateEdges
|
Controls how duplicate edges (i.e., edges that are present multiple
times) are handled. Such edges may be present in the input, or they can
be created when vertices are snapped together. When several edges are
merged, the result is a single edge labelled with all of the original
input edge ids.
|
SiblingPairs
|
Controls how sibling edge pairs (i.e., pairs consisting of an edge and
its reverse edge) are handled. Layer types that define an interior
(e.g., polygons) normally discard such edge pairs since they do not
affect the result (i.e., they define a "loop" with no interior). The
various options include:
|
DegenerateEdges
:DISCARD is specified, then S2Builder will ensure that all
degenerate edges are removed before passing the graph to the S2Layer::Build
method.