Projection and zoom

01 · The Earth constants

Projection, geodesy and tile maths all read from Earth.

03 · Zoom and altitude

2D tile providers express scale as a zoom level; 3D ones as camera altitude or range. MapConductor converts between them so your app always sees one zoom scale. Each provider implements one converter class extending the shared abstract base.

Latitude and tilt are part of the conversion: Web Mercator magnifies towards the poles, so the same zoom level needs a several-fold different camera altitude at the equator and at high latitude.

abstract class AbstractZoomAltitudeConverter(
    protected val zoom0Altitude: Double,
) {
    abstract fun zoomLevelToAltitude(zoomLevel: Double, latitude: Double, tilt: Double): Double

    abstract fun altitudeToZoomLevel(altitude: Double, latitude: Double, tilt: Double): Double
}

public protocol ZoomAltitudeConverterProtocol {
    var zoom0Altitude: Double { get }

    func zoomLevelToAltitude(zoomLevel: Double, latitude: Double, tilt: Double) -> Double
    func altitudeToZoomLevel(altitude: Double, latitude: Double, tilt: Double) -> Double
}

export abstract class AbstractZoomAltitudeConverter {
    constructor(protected readonly zoom0Altitude: number =
        AbstractZoomAltitudeConverter.DEFAULT_ZOOM0_ALTITUDE) {}

    abstract zoomLevelToAltitude(params: { zoomLevel: number; latitude: number; tilt: number }): number;
    abstract altitudeToZoomLevel(params: { altitude: number; latitude: number; tilt: number }): number;
}

Each provider package ships its own ZoomAltitudeConverter. Your app does not normally call it, but it is available if you are building your own 3D presentation.

// The same camera position handed to both states
val shared = MapCameraPosition(
    position = GeoPoint.fromLatLong(35.6812, 139.7671),
    zoom = 14.0,
)
val maplibre = rememberMapLibreMapViewState(cameraPosition = shared)
val googlemaps = rememberGoogleMapViewState(cameraPosition = shared)

// Move one and the same value goes to the other
Row {
    MapLibreMapView(
        state = maplibre,
        modifier = Modifier.weight(1f),
        onCameraMoveEnd = { googlemaps.moveCameraTo(it) },
    )
    GoogleMapView(
        state = googlemaps,
        modifier = Modifier.weight(1f),
        onCameraMoveEnd = { maplibre.moveCameraTo(it) },
    )
}