/// <summary>
/// Create a LinkedGeoPolygon describing the outline(s) of a set of hexagons.
/// Polygon outlines will follow GeoJSON MultiPolygon order: Each polygon will
/// have one outer loop, which is first in the list, followed by any holes.
///
/// It is expected that all hexagons in the set have the same resolution and
/// that the set contains no duplicates. Behavior is undefined if duplicates
/// or multiple resolutions are present, and the algorithm may produce unexpected
/// or invalid output.
/// </summary>
/// <param name="h3Set">Set of hexagons</param>
/// <param name="numHexes">NUmber of hexagons in set</param>
/// <param name="out_polygons">output polygon</param>
/// <!-- Based off 3.1.1 -->
public static void h3SetToLinkedGeo(ref List <H3Index> h3Set, int numHexes,
ref LinkedGeo.LinkedGeoPolygon out_polygons)
{
VertexGraph graph = new VertexGraph(0, 0);
h3SetToVertexGraph(ref h3Set, numHexes, ref graph);
_vertexGraphToLinkedGeo(ref graph, ref out_polygons);
// TODO: The return value, possibly indicating an error, is discarded here -
// we should use this when we update the API to return a value
LinkedGeo.normalizeMultiPolygon(ref out_polygons);
VertexGraph.destroyVertexGraph(ref graph);
}
/// <summary>
/// Internal: Create a LinkedGeoPolygon from a vertex graph. It is the
/// responsibility of the caller to call destroyLinkedPolygon on the
/// populated linked geo structure, or the memory for that structure
/// will not be freed.
/// </summary>
/// <param name="graph">input graph</param>
/// <param name="out_polygon">output polygon</param>
/// <!-- Based off 3.1.1 -->
internal static void _vertexGraphToLinkedGeo(ref VertexGraph graph, ref LinkedGeo.LinkedGeoPolygon out_polygon)
{
out_polygon = new LinkedGeo.LinkedGeoPolygon();
VertexGraph.VertexNode edge;
// Find the next unused entry point
while ((edge = VertexGraph.firstVertexNode(ref graph)) != null)
{
var loop = LinkedGeo.addNewLinkedLoop(ref out_polygon);
// Walk the graph to get the outline
do
{
var addLinkedCoord = LinkedGeo.addLinkedCoord(ref loop, ref edge.from);
var nextVertex = edge.to;
// Remove frees the node, so we can't use edge after this
VertexGraph.removeVertexNode(ref graph, ref edge);
edge = VertexGraph.findNodeForVertex(ref graph, ref nextVertex);
} while (edge != null);
}
}
