Builds a sequence from a set of LineStrings so that they are ordered end to end. More...
#include <LineSequencer.h>
Public Member Functions | |
bool | isSequenceable () |
void | add (const geom::Geometry &geometry) |
void | filter (const geom::Geometry *g) |
geom::Geometry * | getSequencedLineStrings (bool release=1) |
Static Public Member Functions | |
static bool | isSequenced (const geom::Geometry *geom) |
Builds a sequence from a set of LineStrings so that they are ordered end to end.
A sequence is a complete non-repeating list of the linear components of the input. Each linestring is oriented so that identical endpoints are adjacent in the list.
The input linestrings may form one or more connected sets. The input linestrings should be correctly noded, or the results may not be what is expected. The output of this method is a single MultiLineString containing the ordered linestrings in the sequence.
The sequencing employs the classic Eulerian path graph algorithm. Since Eulerian paths are not uniquely determined, further rules are used to make the computed sequence preserve as much as possible of the input ordering. Within a connected subset of lines, the ordering rules are:
Not all arrangements of lines can be sequenced. For a connected set of edges in a graph, Euler's Theorem states that there is a sequence containing each edge once if and only if there are no more than 2 nodes of odd degree. If it is not possible to find a sequence, the isSequenceable method will return false
.
void geos::operation::linemerge::LineSequencer::add | ( | const geom::Geometry & | geometry | ) | [inline] |
Adds a Geometry to be sequenced. May be called multiple times. Any dimension of Geometry may be added; the constituent linework will be extracted.
geometry | the geometry to add |
References geos::geom::Geometry::applyComponentFilter().
void geos::operation::linemerge::LineSequencer::filter | ( | const geom::Geometry * | g | ) | [inline] |
Act as a GeometryComponentFilter so to extract the linearworks
geom::Geometry* geos::operation::linemerge::LineSequencer::getSequencedLineStrings | ( | bool | release = 1 |
) | [inline] |
Returns the LineString or MultiLineString built by the sequencing process, if one exists.
release | release ownership of computed Geometry |
null
if a valid sequence does not exist. bool geos::operation::linemerge::LineSequencer::isSequenceable | ( | ) | [inline] |
Tests whether the arrangement of linestrings has a valid sequence.
true
if a valid sequence exists. static bool geos::operation::linemerge::LineSequencer::isSequenced | ( | const geom::Geometry * | geom | ) | [static] |
Tests whether a Geometry is sequenced correctly. { LineString}s are trivially sequenced. MultiLineStrings are checked for correct sequencing. Otherwise, isSequenced
is defined to be true
for geometries that are not lineal.
geom | the geometry to test |