Module Geojsonm

A library for manipulating large GeoJson documents without reading the whole document into memory using the Jsonm streaming, JSON parser.

module Err : sig ... end
module G : Geojson.S with type json = Ezjsonm.value

Maps

Maps are functions that allow you to manipulate common structure in GeoJson objects. These will be written directly back to the destination that you provide.

val map_geometry : (G.Geometry.t -> G.Geometry.t) -> Jsonm.src -> Jsonm.dst -> (unit, Err.t) Stdlib.result

map_geometry f src dst will apply f to all GeoJson objects. This is essentially any geometry object.

The map will recurse into geometry collections. Note for the moment if you have a single geometry object as your document, this will not work.

val map_props : (Ezjsonm.value -> Ezjsonm.value) -> Jsonm.src -> Jsonm.dst -> (unit, Err.t) Stdlib.result

map_props src dst ~f will apply f to each feature's properties field. The properties field is decoded into an Ezjsonm.value for convenience.

Folds

Folds are like maps except you can collect items into an accumulator which is returned to you.

For example, you might want to collect all of the names in the properties of features.

let get_string_exn = function `String s -> s | _ -> failwith "err"

let get_name = function
  | `O assoc -> List.assoc "name" assoc |> get_string_exn
  | _ -> failwith "err"

let places src =
  Geojsonm.fold_props (fun acc p -> get_name p :: acc) [] src
val fold_geometry : ('a -> G.Geometry.t -> 'a) -> 'a -> Jsonm.src -> ('a, Err.t) Stdlib.result

fold_geometry f acc src is much like map_geometry but allows you to accumulate some result that is then returned to you.

val fold_props : ('a -> Ezjsonm.value -> 'a) -> 'a -> Jsonm.src -> ('a, Err.t) Stdlib.result

fold_props f init src