public async Task <IEnumerable <GeoClusterLocation> > GetGeoLocationClustersAsync(
GetGeoLocationClustersRequest request,
CancellationToken cancellationToken)
{
IEnumerable <MediaGeoLocation> medias = await _mediaStore.FindMediaInGeoBoxAsync(
request.Box,
100000,
cancellationToken);
var clusters = new List <GeoClusterLocation>();
if (medias.Count() < 500 && request.Precision > 10)
{
//Add every item as cluster
foreach (MediaGeoLocation media in medias)
{
clusters.Add(new GeoClusterLocation()
{
Hash = GeoHash.Encode(
media.Coordinates.Latitude,
media.Coordinates.Longitude),
Coordinates = media.Coordinates,
Id = media.Id,
Count = 1
});
}
}
else
{
medias.ToList().ForEach(x => x.GeoHash = x.GeoHash.Substring(0, request.Precision));
IEnumerable <IGrouping <string, MediaGeoLocation> > grouped = medias
.GroupBy(x => x.GeoHash);
foreach (IGrouping <string, MediaGeoLocation>?group in grouped)
{
GeohashDecodeResult decoded = GeoHash.Decode(group.Key);
var cluster = new GeoClusterLocation
{
Hash = group.Key,
Count = group.Count(),
Coordinates = new GeoCoordinate
{
Latitude = decoded.Coordinates.Lat,
Longitude = decoded.Coordinates.Lon
}
};
if (group.Count() == 1)
{
cluster.Id = group.First().Id;
}
clusters.Add(cluster);
}
}
return(clusters);
}
/// <summary>
/// Bounding Circle
/// Get all the hashString covered by the circle in numberOfChars
/// </summary>
/// <param name="latitude">latitude of center point</param>
/// <param name="longitude">longitude of center point</param>
/// <param name="radius">radius in meters</param>
/// <param name="numberOfChars">number of characters of hash string</param>
/// <returns>hash string array</returns>
public static string[] Bcircle(double latitude, double longitude, double radius, int numberOfChars = 9)
{
var hashList = new List <string>();
string hashCenter = GeoHash.Encode(latitude, longitude, numberOfChars);
hashList.Add(hashCenter);
GeohashDecodeResult latLon = GeoHash.Decode(hashCenter);
// Find left and right end
// Find west(left) end
Coordinates leftCoor = DistanceToPoint(latitude, longitude, radius, 270);
string hashLeft = GeoHash.Encode(leftCoor.Lat, leftCoor.Lon, numberOfChars);
NGeoHash.BoundingBox boxLeft = GeoHash.DecodeBbox(hashLeft);
// Find east(right) end
Coordinates rightCoor = DistanceToPoint(latitude, longitude, radius, 90);
string hashRight = GeoHash.Encode(rightCoor.Lat, rightCoor.Lon, numberOfChars);
NGeoHash.BoundingBox boxRight = GeoHash.DecodeBbox(hashRight);
// Find steps(from left to right)
double perLon = latLon.Error.Lon * 2; // box size(in degree) on west-east direction
var lonStep = Math.Round((boxRight.Minimum.Lon - boxLeft.Minimum.Lon) / perLon);
double perLat = latLon.Error.Lat * 2; // box size(in dgree) on north–south direction
for (var lon = 0; lon <= lonStep; lon++)
{
// Find current box
string currentBoxHash = GeoHash.Neighbor(hashLeft, new[] { 0, lon });
NGeoHash.BoundingBox currentBox = GeoHash.DecodeBbox(currentBoxHash);
// Find north(upper) end
// Find up neighbor
// Check if in range
int i = 0;
NGeoHash.BoundingBox upBox = currentBox;
string upBoxHash = currentBoxHash;
while (BoxInCircleRange(upBox, latitude, longitude, radius))
{
if (!hashList.Contains(upBoxHash))
{
hashList.Add(upBoxHash);
}
//Console.WriteLine("Add+ " + upBoxHash);
i++;
upBoxHash = GeoHash.Neighbor(currentBoxHash, new[] { i, 0 });
upBox = GeoHash.DecodeBbox(upBoxHash);
}
// Find south(down) end
// Find steps(north to south)
int j = 0;
NGeoHash.BoundingBox downBox = currentBox;
string downBoxHash = currentBoxHash;
while (BoxInCircleRange(downBox, latitude, longitude, radius))
{
if (!hashList.Contains(downBoxHash))
{
hashList.Add(downBoxHash);
}
//Console.WriteLine("Add- " + downBoxHash);
j--;
downBoxHash = GeoHash.Neighbor(currentBoxHash, new[] { j, 0 });
downBox = GeoHash.DecodeBbox(downBoxHash);
}
}
// Check each point on the circle, see if covers more box
// Find step length of radius
double stepOfRadius = FindMinSideLength(hashCenter) * 0.9;
// Find step of cricle, devide 360 degree to how many parts
double stepOfCircle = 360 / (Math.PI * 2 * radius / stepOfRadius);
for (double degree = 0; degree <= 360; degree += stepOfCircle)
{
Coordinates coor = DistanceToPoint(latitude, longitude, radius, degree);
string hash = GeoHash.Encode(coor.Lat, coor.Lon, numberOfChars);
if (!hashList.Contains(hash))
{
hashList.Add(hash);
}
}
return(hashList.ToArray());
}
