/// <summary>
/// _polyfillInternal traces the provided geoPolygon data structure with hexagons
/// and then iteratively searches through these hexagons and their immediate
/// neighbors to see if they are contained within the polygon or not. Those that
/// are found are added to the out array as well as the found array. Once all
/// hexagons to search are checked, the found hexagons become the new search
/// array and the found array is wiped and the process repeats until no new
/// hexagons can be found.
/// </summary>
/// <remarks>
/// This comes at it a little differently using C#'s internal HashSet rather
/// than a collision bucket. I've tweaked it to where it matches the speed
/// of the original in benchmark tests, but it liekly could be made faster.
/// </remarks>
/// <param name="polygon">The geofence and holes defining the relevant area</param>
/// <param name="res">The Hexagon resolution (0-15)</param>
/// <returns>
/// Tuple
/// Item1 - Status code
/// Item2 - List of H3Index values
/// </returns>
/// <!--
/// algos.c
/// int _polyfillInternal
/// -->
public static (int, List <H3Index>) PolyFillInternal(this GeoPolygon polygon, int res)
{
// Get bounding boxes
var bboxes = polygon.ToBBoxes();
// Get the traced hexagons around the outer polygon;
var geofence = polygon.GeoFence;
var preSearch = new List <H3Index>();
var search = geofence.GetEdgeHexagons(res);
preSearch.AddRange(search);
// Check inner holes
for (var i = 0; i < polygon.NumHoles; i++)
{
var hole = polygon.Holes[i];
var innerHex = hole.GetEdgeHexagons(res);
preSearch.AddRange(innerHex);
}
search = new HashSet <H3Index>();
search.UnionWith(preSearch);
var found = new HashSet <H3Index>();
var results = new HashSet <H3Index>();
int numSearchHexes = search.Count;
var numFoundHexes = 0;
while (numSearchHexes > 0)
{
var currentSearchNum = 0;
while (currentSearchNum < numSearchHexes)
{
foreach (var ring in search
.Select
(
index => index.KRing(1)
.Where(h => h != Constants.H3Index.H3_NULL)
))
{
foreach (
var hex in ring
.Where
(
hex => !results.Contains(hex) &&
!found.Contains(hex) &&
polygon.PointInside(bboxes, hex.ToGeoCoord())
))
{
found.Add(hex);
numFoundHexes++;
}
currentSearchNum++;
}
}
search = new HashSet <H3Index>(found);
numSearchHexes = numFoundHexes;
numFoundHexes = 0;
results.UnionWith(found);
found.Clear();
}
return(0, results.ToList());
}
