public GeoHash(double latitude, double longitude, int precision = DefaultPrecision)
{
if (precision < 1)
{
throw new ArgumentException("Precision of GeoHash must be larger than zero!");
}
if (precision > MaxPrecision)
{
throw new ArgumentException("Precision of a GeoHash must be less than " + (MaxPrecision + 1) + "!");
}
if (!GeoUtils.CoordinatesValid(latitude, longitude))
{
throw new ArgumentException(string.Format("Not valid location coordinates: [%f, %f]", latitude, longitude));
}
double[] longitudeRange = { -180, 180 };
double[] latitudeRange = { -90, 90 };
var buffer = new char[precision];
for (var i = 0; i < precision; i++)
{
var hashValue = 0;
for (var j = 0; j < Base32Utils.BitsPerBase32Char; j++)
{
var even = (i * Base32Utils.BitsPerBase32Char + j) % 2 == 0;
var val = even ? longitude : latitude;
var range = even ? longitudeRange : latitudeRange;
var mid = (range[0] + range[1]) / 2;
if (val > mid)
{
hashValue = (hashValue << 1) + 1;
range[0] = mid;
}
else
{
hashValue <<= 1;
range[1] = mid;
}
}
buffer[i] = Base32Utils.ValueToBase32Char(hashValue);
}
_geoHash = new string(buffer);
}
public static GeoHashQuery QueryForGeoHash(GeoHash geohash, int bits)
{
var hash = geohash.GetGeoHashString();
var precision = (int)Math.Ceiling((double)bits / Base32Utils.BitsPerBase32Char);
if (hash.Length < precision)
{
return(new GeoHashQuery(hash, hash + "~"));
}
hash = hash.Substring(0, precision);
var hashBase = hash.Substring(0, hash.Length - 1);
var lastValue = Base32Utils.Base32CharToValue(hash[hash.Length - 1]);
var significantBits = bits - hashBase.Length * Base32Utils.BitsPerBase32Char;
var unusedBits = Base32Utils.BitsPerBase32Char - significantBits;
// delete unused bits
var startValue = (lastValue >> unusedBits) << unusedBits;
var endValue = startValue + (1 << unusedBits);
var startHash = hashBase + Base32Utils.ValueToBase32Char(startValue);
var endHash = endValue > 31 ? hashBase + "~" : hashBase + Base32Utils.ValueToBase32Char(endValue);
return(new GeoHashQuery(startHash, endHash));
}