Encodes a GeoJSON object into a JSON value.

This function takes a GeoJSON object and a properties encoder function, and returns a JSON representation of the GeoJSON object.

Arguments

• geojson: The GeoJSON object to encode.
• properties_encoder: A function that encodes the properties of Features and FeatureCollections.

Returns

A JSON representation of the GeoJSON object.

Example

import gleojson
import gleam/json
import gleam/option
import gleam/io

pub type CustomProperties {
  CustomProperties(name: String, value: Float)
}

pub fn custom_properties_encoder(props: CustomProperties) -> json.Json {
  json.object([
    #("name", json.string(props.name)),
    #("value", json.float(props.value)),
  ])
}

pub fn main() {
  let point = gleojson.Point(gleojson.position_2d(lon: 0.0, lat: 0.0))
  let properties = CustomProperties("Example", 42.0)
  let feature = gleojson.Feature(
    geometry: option.Some(point),
    properties: option.Some(properties),
    id: option.Some(gleojson.StringId("example-point"))
  )
  
  let encoded = gleojson.encode_geojson(feature, custom_properties_encoder)
  io.println(json.to_string(encoded))
}

Encodes a GeoJSON geometry object into a JSON value.

This function is a convenience wrapper around encode_geojson for geometry objects.

Decodes a GeoJSON object from a dynamic value.

This function takes a dynamic value (typically parsed from JSON) and a properties decoder, and attempts to decode it into a GeoJSON object.

Arguments

• properties_decoder: A function that decodes the properties of Features and FeatureCollections.

Returns

A function that takes a dynamic value and returns a Result containing either the decoded GeoJSON object or a list of decode errors.

Example

import gleojson
import gleam/json
import gleam/result
import gleam/dynamic
import gleam/io
import gleam/string

pub type CustomProperties {
  CustomProperties(name: String, value: Float)
}

pub fn custom_properties_decoder(
  dyn: dynamic.Dynamic,
) -> Result(CustomProperties, List(dynamic.DecodeError)) {
  dynamic.decode2(
    CustomProperties,
    dynamic.field("name", dynamic.string),
    dynamic.field("value", dynamic.float),
  )(dyn)
}

pub fn main() {
  let json_string = "{\"type\":\"Feature\",\"geometry\":{\"type\":\"Point\",\"coordinates\":[0.0,0.0]},\"properties\":{\"name\":\"Example\",\"value\":42.0}}"
  
  let decoded = 
    json.decode(
      from: json_string,
      using: gleojson.geojson_decoder(custom_properties_decoder)
    )
  
  case decoded {
    Ok(geojson) -> {
      // Work with the decoded GeoJSON object
      case geojson {
        gleojson.Feature(_, _, _) -> {
          io.println("Decoded a feature")
        }
        _ -> io.println("Decoded a different type of GeoJSON object")
      }
    }
    Error(errors) -> {
      // Handle decoding errors
      io.println("Failed to decode: " <> string.join(errors, ", "))
    }
  }
}

Creates a decoder for GeoJSON geometry objects.

This function is a convenience wrapper around geojson_decoder for geometry objects.

Creates a 2D Position object from longitude and latitude values.

This function is a convenience helper for creating a Position object with two dimensions (longitude and latitude).

Arguments

• lon: The longitude value as a Float.
• lat: The latitude value as a Float.

Returns

A Position object representing a 2D coordinate.

Example

import gleojson

pub fn main() {
  let position = gleojson.position_2d(lon: 125.6, lat: 10.1)
  // Use this position in your GeoJSON objects, e.g., in a Point geometry
  let point = gleojson.Point(coordinates: position)
}

Creates a 3D Position object from longitude, latitude, and altitude values.

This function is a convenience helper for creating a Position object with three dimensions (longitude, latitude, and altitude).

Arguments

• lon: The longitude value as a Float.
• lat: The latitude value as a Float.
• alt: The altitude value as a Float.

Returns

A Position object representing a 3D coordinate.

Example

import gleojson

pub fn main() {
  let position = gleojson.position_3d(lon: 125.6, lat: 10.1, alt: 100.0)
  // Use this position in your GeoJSON objects, e.g., in a Point geometry
  let point = gleojson.Point(coordinates: position)
}

Decodes null properties for Features and FeatureCollections.

This is a utility function that can be used as the properties_decoder argument for geojson_decoder when you don’t need to decode any properties.

Encodes null properties for Features and FeatureCollections.

This is a utility function that can be used as the properties_encoder argument for encode_geojson when you don’t need to encode any properties.