llamadonica / dart-geohash Goto Github PK

As a user of this lib, I want to be able to easily create a hash search query, so that I can query databases quickly and consistently.

Supporting info
Here's a discussion of how to make a list of hashes to perform a location based search
https://gis.stackexchange.com/questions/18330/using-geohash-for-proximity-searches
And an even older article
https://www.movable-type.co.uk/scripts/geohash.html

AC

• Add something like String[] getHashesByRadius(lat, long, radius)

With respect to

static Rectangle<double> getExtents(String geohash) 

the values calculated in the block below are correct.

      final latitude = latitudeFloat * (180 / pow(2.0, 52)) - 90;
      final longitude = longitudeFloat * (360 / pow(2.0, 52)) - 180;
      final height = latitudeDiff * (180 / pow(2.0, 52));
      final width = longitudeDiff * (360 / pow(2.0, 52));

However, the computed latitude and longitude represent the top left corner of the geohash block.

Therefore:

return Rectangle<double>(latitude + height, longitude, height, width);

should be:

return Rectangle<double>(longitude, latitude, width, height);   //  Rectangle params: Rectangle(this.left, this.top, T width, T height)

Moreover, while latitude decreases downward - this is the definition of bottom for Rectangle:

/// The y-coordinate of the bottom edge.
  T get bottom => (top + height) as T;

Therefore, with respect to:

static Point<double> decode(String geohash)

The computations of the coordinates should be:

    final x = extents.left + extents.width / 2;
    final y = extents.bottom - extents.height / 2;

I have used x=longitude and y=latitude based on the commonly accepted mathematical approach of used x to represent the horizontal axis and y to represent the vertical axis. I recommend this is implemented. It may be a breaking change but the code isn't functional anyway.