A multipart geometry can be densified by adding interpolated points at regular intervals. Generalizing multipart geometry simplifies it while preserving its general shape. Densifying a multipart geometry adds more vertices at regular intervals.
Use case
The sample shows a polyline representing a ship's location at irregular intervals. The density of vertices along the ship's route is appropriate to represent the path of the ship at the sample map view's initial scale. However, that level of detail may be too great if you wanted to show a polyline of the ship's movement down the whole of the Willamette river. Then, you might consider generalizing the polyline to still faithfully represent the ship's passage on the river without having an overly complicated geometry.
Densifying a multipart geometry can be used to more accurately represent curved lines or to add more regularity to the vertices making up a multipart geometry.
How to use the sample
Tap the "Option" button to open the settings. Use the sliders to control the parameters of the densify and generalize methods. You can deselect the toggles for either method to remove its effect from the result polyline.
How it works
- Use the static method
static GeometryEngine.densify(_:maxSegmentLength:)to densify the polyline object. The resulting polyline object will have more points along the line, so that there are no points greater thanmaxSegmentLengthfrom the next point. - Use the static method
static GeometryEngine.generalize(_:maxDeviation:removeDegenerateParts:)to generalize the polyline object. The resulting polyline object will have points shifted from the original line to simplify the shape. None of these points can deviate farther from the original line thanmaxDeviation. The last parameter,removeDegenerateParts, will clean up extraneous parts of a multipart geometry. This will have no effect in this sample as the polyline does not contain extraneous parts. - Note that
maxSegmentLengthandmaxDeviationare in the units of the geometry's coordinate system. In this example, a cartesian coordinate system is used and at a small enough scale that geodesic distances are not required.
Relevant API
- GeometryEngine
- Multipoint
- Point
- PointCollection
- Polyline
- SimpleLineSymbol
- SpatialReference
Tags
densify, generalize, simplify
Sample Code
// Copyright 2023 Esri // // Licensed under the Apache License, Version 2.0 (the "License"); // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // // https://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. // See the License for the specific language governing permissions and // limitations under the License. import ArcGIS import SwiftUI struct DensifyAndGeneralizeGeometryView: View { /// The view model for the sample. @StateObject private var model = Model() /// A Boolean value indicating whether the geometry settings sheet is showing. @State private var isShowingSettings = false var body: some View { MapView(map: model.map, graphicsOverlays: [model.graphicsOverlay]) .toolbar { ToolbarItem(placement: .bottomBar) { Button("Geometry Settings") { isShowingSettings = true } .popover(isPresented: $isShowingSettings) { NavigationStack { SettingsView(model: model) } .presentationDetents([.fraction(0.5)]) .frame(idealWidth: 320, idealHeight: 380) } } } } } extension DensifyAndGeneralizeGeometryView { /// The view model for the sample. class Model: ObservableObject { /// A map with a Streets (Night) basemap. let map = Map(basemapStyle: .arcGISStreetsNight) /// The graphics overlay for all of the graphics. let graphicsOverlay: GraphicsOverlay /// The base polyline geometry that is densified and generalized. private let originalPolyline: Polyline /// The graphic for displaying the points of the resultant geometry. private let resultPointsGraphic: Graphic = { let symbol = SimpleMarkerSymbol(style: .circle, color: .magenta, size: 7) return Graphic(symbol: symbol) }() /// The graphic for displaying the lines of the resultant geometry. private let resultPolylineGraphic: Graphic = { let symbol = SimpleLineSymbol(style: .solid, color: .magenta, width: 3) return Graphic(symbol: symbol) }() /// A mutable point collection from which the original polyline and /// multipoint geometries are made. private let pointCollection = MutablePointCollection( points: [ Point(x: 2330611.130549, y: 202360.002957), Point(x: 2330583.834672, y: 202525.984012), Point(x: 2330574.164902, y: 202691.488009), Point(x: 2330689.292623, y: 203170.045888), Point(x: 2330696.773344, y: 203317.495798), Point(x: 2330691.419723, y: 203380.917080), Point(x: 2330435.065296, y: 203816.662457), Point(x: 2330369.500800, y: 204329.861789), Point(x: 2330400.929891, y: 204712.129673), Point(x: 2330484.300447, y: 204927.797132), Point(x: 2330514.469919, y: 205000.792463), Point(x: 2330638.099138, y: 205271.601116), Point(x: 2330725.315888, y: 205631.231308), Point(x: 2330755.640702, y: 206433.354860), Point(x: 2330680.644719, y: 206660.240923), Point(x: 2330386.957926, y: 207340.947204), Point(x: 2330485.861737, y: 207742.298501) ], // The spatial reference for the sample, NAD83 / Oregon North. spatialReference: SpatialReference(wkid: WKID(rawValue: 32126)!) ) /// A Boolean indicating whether to generalize. @Published var shouldGeneralize = false /// The max deviation for generalization. @Published var maxDeviation = 10.0 /// A Boolean indicating whether to densify. @Published var shouldDensify = false /// The max segment length for densifying. @Published var maxSegmentLength = 100.0 init() { originalPolyline = Polyline(points: pointCollection) // Set the initial viewpoint to show the extent of the polyline. map.initialViewpoint = Viewpoint( center: originalPolyline.extent.center, scale: 65907 ) // Create graphics overlay. let multipoint = Multipoint(points: pointCollection) // Create graphics for displaying the base points and lines. let originalPolylineGraphic = Graphic( geometry: originalPolyline, symbol: SimpleLineSymbol(style: .dot, color: .red, width: 3) ) let originalPointsGraphic = Graphic( geometry: multipoint, symbol: SimpleMarkerSymbol(style: .circle, color: .red, size: 7) ) // Add the graphics in the order we want them to appear, back to front. graphicsOverlay = GraphicsOverlay(graphics: [ originalPointsGraphic, originalPolylineGraphic, resultPointsGraphic, resultPolylineGraphic ]) } /// Resets the model values to the originals. func reset() { shouldDensify = false maxDeviation = 10.0 shouldGeneralize = false maxSegmentLength = 100.0 updateGraphics() } /// Updates the result polyline and multipoint graphics after densifying /// and generalizing. func updateGraphics() { // Reset the result graphics if there are no operations to do. if !shouldGeneralize && !shouldDensify { resultPolylineGraphic.geometry = nil resultPointsGraphic.geometry = nil return } // Start with original polyline. var resultPolyline = originalPolyline // Generalize the polyline with the specified max deviation. if shouldGeneralize { resultPolyline = GeometryEngine.generalize( resultPolyline, maxDeviation: maxDeviation, removeDegenerateParts: true ) as! Polyline } // Densify the points of the polyline with the specified max segment. if shouldDensify { resultPolyline = GeometryEngine.densify( resultPolyline, maxSegmentLength: maxSegmentLength ) as! Polyline } // Convert the result points to an array. let points = resultPolyline.parts.flatMap(\.points) // Create a multipoint geometry from the points array. let resultMultipoint = Multipoint(points: points) // Update the result graphics with the result geometries. resultPolylineGraphic.geometry = resultPolyline resultPointsGraphic.geometry = resultMultipoint } } } #Preview { NavigationStack { DensifyAndGeneralizeGeometryView() } }