geohash-dotnet

An easy-to-use, feature-rich geohash library for .NET

Installation

Install via NuGet Package Manager:

 Install-Package geohash-dotnet

Features

Geohasher

• Encode/Decode: Convert between geographic coordinates and geohash strings.
• Neighbors: Find adjacent geohashes in all cardinal directions.
• Subhashes: Retrieve finer-grained geohashes within a parent geohash.
• Parent Geohash: Get the less precise parent of a given geohash.
• Bounding Box: Obtain the geographic bounding box of a geohash.

PolygonHasher

• Generate geohashes within a specified polygon based on precision and inclusion criteria.
• Ideal for spatial indexing and geospatial queries within complex areas.

GeohashCompressor

• Compresses a set of geohashes to a minimal set that still covers the same area.
• Optimizes storage and improves performance for spatial queries.

Geohasher

Generate geohashes that cover a specific polygon:

// Create a new Geohasher instance
var geohasher = new Geohasher();

// Encode latitude and longitude into a geohash string
string geohash = geohasher.Encode(37.4219999, -122.0840575, 9);

// Decode the geohash back to latitude and longitude
(double latitude, double longitude) = geohasher.Decode(geohash);

// Get subhashes of a geohash
string[] subhashes = geohasher.GetSubhashes(geohash);

// Get neighbors of a geohash
Dictionary<Direction, string> neighbors = geohasher.GetNeighbors(geohash);

// Get parent of a geohash
string parent = geohasher.GetParent(geohash);

// Get the bounding box of a geohash
BoundingBox bbox = geohasher.GetBoundingBox(geohash);

PolygonHasher

// Initialize PolygonHasher
var polygonHasher = new PolygonHasher();

// Define a polygon
Polygon polygon = new Polygon(new LinearRing(new Coordinate[] {
  new Coordinate(-122.4183, 37.7755),
  new Coordinate(-122.4183, 37.7814),
  new Coordinate(-122.4085, 37.7814),
  new Coordinate(-122.4085, 37.7755),
  new Coordinate(-122.4183, 37.7755) // Closing the ring
}));

// Get geohashes of precision 6 that intersect with the polygon
var geohashes = polygonHasher.GetHashes(polygon, 6, PolygonHasher.GeohashInclusionCriteria.Intersects);

// Output the geohashes
foreach (string hash in geohashes)
{
  Console.WriteLine(hash);
}

GeohashCompressor

Compress a list of geohashes into a minimal covering set:

// Initialize GeohashCompressor
var compressor = new GeohashCompressor();

// Define input geohashes
var inputGeohashes = new[] {
  "tdnu20", "tdnu21", "tdnu22", "tdnu23", "tdnu24", "tdnu25",
  "tdnu26", "tdnu27", "tdnu28", "tdnu29", "tdnu2b", "tdnu2c",
  // ... additional geohashes
};

// Compress the geohashes
var compressedGeohashes = compressor.Compress(inputGeohashes);

// Output the compressed geohashes
foreach (var hash in compressedGeohashes)
{
  Console.WriteLine(hash);
}

Finding Neighbors

Dictionary<Direction, string> neighbors = geohasher.GetNeighbors(geohash);

string northNeighbor = neighbors[Direction.North];
string southNeighbor = neighbors[Direction.South];
// ... and so on for the other directions

find the neighbor hash in a specific direction, use the GetNeighbor() method:

string northNeighbor = geohasher.GetNeighbor(geohash, Direction.North);

Subhashes

Subhashes represent smaller, equally-sized regions within a geohash's bounding box:

string[] subhashes = geohasher.GetSubhashes(geohash);

Parent Geohash

The parent of a geohash is the geohash that covers the same area but at a lower precision level:

string parent = geohasher.GetParent(geohash);

Keep in mind that the parent geohash will be less precise and cover a larger area.

Bounding Box

To obtain the bounding box (minimum and maximum latitude and longitude):

BoundingBox bbox = geohasher.GetBoundingBox(geohash);

Performance Notes

PolygonHasher and GeohashCompressor have a time complexity of O(N²) relative to the number of geohashes processed.