geojson-types

GeoJSON data types including JSON/BSON conversion.

Provides data types, lens operators and (de)serialization of GeoJSON data to/from JSON and BSON using aeson and bson.

This library uses a the lens library a lot. It provides Iso / Prism to convert from and to GeoJSON objects.

e.g. to convert a latitude/longitude given as a pair of Double to a Position, use the _PositionIso as a Getter on that pair:

_Position :: BaseType t => Iso' (t, t) (Position t)

pos :: Position Double
pos = (57.324, 7.2342) ^. _Position

to then convert it to a Point object use _Point:

_Point :: Iso' (Position t) (GeoJSON Point t)

p :: GeoJSON Point Double
p = pos ^. _Point

ps :: GeoJSON MultiPoint Double
ps = [p,p,p,p] ^. _MultiPoint

The library also provides type classes for working polymorphic over user defined data types.

e.g. for a data type:

data Location =
  Location {
    locationName :: String,
    locationLat :: Double,
    locationLon :: Double
  }

one can implement the type class HasGeoJSON to provide a Getter to a any GeoJSON object. In this example a Point.

instance HasGeoJSON Point Double Location where
 geoJSON = to $ \loc ->
   (locationLat loc, locationLon loc) ^. _Position . _Point