c79b6dcf52
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
110 lines
4.8 KiB
Markdown
110 lines
4.8 KiB
Markdown
# Using GeoJSON with a line style layer
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Adding an ``MLNLineStyleLayer`` to the map using a GeoJSON file.
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> Note: This example uses UIKit.
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<!-- include-example(LineStyleLayerExample) -->
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```swift
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class LineStyleLayerExample: UIViewController, MLNMapViewDelegate {
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var mapView: MLNMapView!
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override func viewDidLoad() {
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super.viewDidLoad()
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mapView = MLNMapView(frame: view.bounds, styleURL: VERSATILES_COLORFUL_STYLE)
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mapView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
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mapView.setCenter(
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CLLocationCoordinate2D(latitude: 45.5076, longitude: -122.6736),
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zoomLevel: 11,
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animated: false
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)
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view.addSubview(mapView)
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mapView.delegate = self
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}
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// Wait until the map is loaded before adding to the map.
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func mapView(_: MLNMapView, didFinishLoading _: MLNStyle) {
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loadGeoJson()
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}
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func loadGeoJson() {
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DispatchQueue.global().async {
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// Get the path for example.geojson in the app’s bundle.
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guard let jsonUrl = Bundle.main.url(forResource: "example", withExtension: "geojson") else {
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preconditionFailure("Failed to load local GeoJSON file")
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}
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guard let jsonData = try? Data(contentsOf: jsonUrl) else {
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preconditionFailure("Failed to parse GeoJSON file")
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}
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DispatchQueue.main.async {
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self.drawPolyline(geoJson: jsonData)
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}
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}
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}
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func drawPolyline(geoJson: Data) {
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// Add our GeoJSON data to the map as an MLNGeoJSONSource.
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// We can then reference this data from an MLNStyleLayer.
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// MLNMapView.style is optional, so you must guard against it not being set.
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guard let style = mapView.style else { return }
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guard let shapeFromGeoJSON = try? MLNShape(data: geoJson, encoding: String.Encoding.utf8.rawValue) else {
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fatalError("Could not generate MLNShape")
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}
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let source = MLNShapeSource(identifier: "polyline", shape: shapeFromGeoJSON, options: nil)
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style.addSource(source)
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// Create new layer for the line.
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let layer = MLNLineStyleLayer(identifier: "polyline", source: source)
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// Set the line join and cap to a rounded end.
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layer.lineJoin = NSExpression(forConstantValue: "round")
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layer.lineCap = NSExpression(forConstantValue: "round")
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// Set the line color to a constant blue color.
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layer.lineColor = NSExpression(forConstantValue: UIColor(red: 59 / 255, green: 178 / 255, blue: 208 / 255, alpha: 1))
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// Use `NSExpression` to smoothly adjust the line width from 2pt to 20pt between zoom levels 14 and 18. The `interpolationBase` parameter allows the values to interpolate along an exponential curve.
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layer.lineWidth = NSExpression(forMLNInterpolating: NSExpression.zoomLevelVariable, curveType: MLNExpressionInterpolationMode.linear, parameters: nil, stops: NSExpression(forConstantValue: [14: 2, 18: 20]))
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// We can also add a second layer that will draw a stroke around the original line.
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let casingLayer = MLNLineStyleLayer(identifier: "polyline-case", source: source)
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// Copy these attributes from the main line layer.
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casingLayer.lineJoin = layer.lineJoin
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casingLayer.lineCap = layer.lineCap
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// Line gap width represents the space before the outline begins, so should match the main line’s line width exactly.
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casingLayer.lineGapWidth = layer.lineWidth
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// Stroke color slightly darker than the line color.
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casingLayer.lineColor = NSExpression(forConstantValue: UIColor(red: 41 / 255, green: 145 / 255, blue: 171 / 255, alpha: 1))
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// Use `NSExpression` to gradually increase the stroke width between zoom levels 14 and 18.
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casingLayer.lineWidth = NSExpression(forMLNInterpolating: NSExpression.zoomLevelVariable, curveType: MLNExpressionInterpolationMode.linear, parameters: nil, stops: NSExpression(forConstantValue: [14: 1, 18: 4]))
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// Just for fun, let’s add another copy of the line with a dash pattern.
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let dashedLayer = MLNLineStyleLayer(identifier: "polyline-dash", source: source)
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dashedLayer.lineJoin = layer.lineJoin
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dashedLayer.lineCap = layer.lineCap
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dashedLayer.lineColor = NSExpression(forConstantValue: UIColor.white)
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dashedLayer.lineOpacity = NSExpression(forConstantValue: 0.5)
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dashedLayer.lineWidth = layer.lineWidth
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// Dash pattern in the format [dash, gap, dash, gap, ...]. You’ll want to adjust these values based on the line cap style.
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dashedLayer.lineDashPattern = NSExpression(forConstantValue: [0, 1.5])
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style.addLayer(layer)
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style.addLayer(dashedLayer)
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style.insertLayer(casingLayer, below: layer)
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}
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}
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```
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Map Data from OpenStreetMap.
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