Polyline

The polyline-encoding module encodes and decodes polylines using Google’s Encoded Polyline Algorithm Format.

val positions =
    listOf(
        Position(longitude = -120.2, latitude = 38.5),
        Position(longitude = -120.95, latitude = 40.7),
        Position(longitude = -126.453, latitude = 43.252),
    )
val encoded = PolylineEncoding.encode(positions)
val decoded = PolylineEncoding.decode(encoded)

Details can be found in the API reference.

Installation

Multiplatform

commonMain {
    dependencies {
        implementation("org.maplibre.spatialk:polyline-encoding:0.8.0")
    }
}

JVM

dependencies {
    implementation("org.maplibre.spatialk:polyline-encoding-jvm:0.8.0")
}

Encoding

PolylineEncoding.encode converts a list of Position values into a compact encoded string.

val encoded =
    PolylineEncoding.encode(
        listOf(
            Position(longitude = -120.2, latitude = 38.5),
            Position(longitude = -120.95, latitude = 40.7),
        )
    )

Decoding

PolylineEncoding.decode converts an encoded polyline string back into a list of Position values. It throws IllegalArgumentException if the input is malformed.

val positions = PolylineEncoding.decode("_p~iF~ps|U_ulLnnqC")

PolylineEncoding.decodeOrNull behaves the same way, but returns null on malformed input instead of throwing.

val positions = PolylineEncoding.decodeOrNull("_p~iF~ps|U_ulLnnqC")

Precision

All three methods accept an optional precision parameter that controls the number of decimal digits used for coordinate values. The default is 5, which matches the standard Google precision of 1e-5. Some services, such as OSRM, use a precision of 6 for 1e-6.

val positions =
    listOf(
        Position(longitude = -120.2, latitude = 38.5),
        Position(longitude = -120.95, latitude = 40.7),
    )
val encoded = PolylineEncoding.encode(positions, precision = 6)
val decoded = PolylineEncoding.decode(encoded, precision = 6)