Convert Kml to GeoJSON format

This application KmlToGeojson, converts Kml and Kmz files into a GeoJSON representation.

Kml is used in Google Earth to display various geographic elements, such as; images, place marks, polygon shapes, and so on.

Similarly GeoJSON is a format for encoding a variety of geographic data structures.

This scala application uses the scalakml library and the play-geojson library to convert Kml to GeoJSON format.

Kml to GeoJSON mapping

Currently the following mapping is implemented.

Kml object -> list of GeoJSON object
Kml Folder -> GeoJSON FeatureCollection
Kml Document -> GeoJSON FeatureCollection
Kml MultiGeometry -> GeoJSON GeometryCollection
Kml Placemark -> GeoJSON Feature
Kml Point -> GeoJSON Point
Kml LineString -> GeoJSON LineString
Kml LinearRing -> GeoJSON LineString
Kml Polygon -> GeoJSON Polygon
Kml LatLonAltBox -> GeoJSON bbox

The GeoJSON Feature "properties" are generated from the following Kml elements:

name, description, address, phoneNumber, styleUrl, visibility, open, 
timeSpan (begin and end), timeStamp (when),
extendedData (displayName, name, value), altitudeMode, extrude

The Kml "id" attribute is converted to the GeoJSON Feature "id".

Everything else is ignored.

Only WGS84 coordinate reference system is supported and all longitudes and latitudes are in decimal degrees.

Installation and packaging

The easiest way to compile and package the application from source is to use SBT. To package the application and all its dependencies into a single jar file type:

sbt assembly

This will produce "kmltogeojson-1.2.jar" in the "./target/scala-2.13" directory.

For convenience a kmltogeojson-1.2.jar file is in the "distrib" directory ready for use.

Usage

Once you have the jar file, simply type at the prompt:

java -jar kmltogeojson-1.2.jar kml_file.kml geojson_file.geojson

where "kml_file.kml" is the Kml file you want to convert, and "geojson_file.geojson" is the destination file with the GeoJSON format results. If the "geojson_file.geojson" is absent, the output is directed to the console.

You can also use this library in your scala code. First add the following dependency to your build.sbt file:

libraryDependencies += "com.github.workingDog" %% "kmltogeojson" % "1.2"

Then, for example:

object TestGeoJson {
  def main(args: Array[String]) {
    // read a kml document from file
    val kml = new KmlFileReader().getKmlFromFile("./kml-files/Sydney.kml")
    // convert the kml document to geojson format
    val geojson = KmlConverter().toGeoJson(kml)
    // print the geojson objects
    geojson.foreach(obj => println(Json.prettyPrint(Json.toJson(obj))))
  }
}

The KmlConverter.scala has one generic method toGeoJson() that takes any of the implemented Kml objects. See also "TestGeoJson".

Dependencies

Depends on the scala scalakml library, and on the scala play-geojson library.

References

1. OGC 07-147r2 Version: 2.2.0, Category: OGC Standard, Editor: Tim Wilson, at http://www.opengeospatial.org/standards/kml

2. Google developers KML Reference, at https://developers.google.com/kml/documentation/kmlreference

3. GeoJSON reference document, at http://geojson.org/geojson-spec.html

Status

Stable.

Using Scala 2.13.1, Java 11 and SBT-1.3.8.