Clip geometry

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Sample viewer app

Clip a geometry with another geometry.

Image of clip geometry

Use case

Create a new set of geometries for analysis (e.g. displaying buffer zones around abandoned coal mine shafts in an area of planned urban development) by clipping intersecting geometries.

How to use the sample

Tap the button to clip the blue graphic with the red dashed envelopes.

How it works

  1. Use the static method class AGSGeometryEngine.clipGeometry(_:with:) to generate a clipped AGSGeometry, passing in an existing AGSGeometry and an AGSEnvelope as parameters. The existing geometry will be clipped where it intersects an envelope.
  2. Create a new AGSGraphic from the clipped geometry and add it to an AGSGraphicsOverlay on the AGSMapView.

Relevant API

  • AGSEnvelope
  • AGSGeometry
  • AGSGraphic
  • AGSGraphicsOverlay
  • class AGSGeometryEngine.clipGeometry(_:with:)

Additional information

Note: the resulting geometry may be null if the envelope does not intersect the geometry being clipped.

Tags

analysis, clip, geometry

Sample Code

ClipGeometryViewController.swift
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// Copyright 2018 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
//
//   http://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 UIKit
import ArcGIS

class ClipGeometryViewController: UIViewController {
    // MARK: Storyboard views

    /// The map view managed by the view controller.
    @IBOutlet var mapView: AGSMapView! {
        didSet {
            // Create a map with a topographic basemap.
            mapView.map = AGSMap(basemapStyle: .arcGISTopographic)
            // Add the graphics overlays to the map view.
            mapView.graphicsOverlays.addObjects(from: [coloradoGraphicsOverlay, envelopesGraphicsOverlay, clippedGraphicsOverlay])
            // Set the viewpoint to the extent of the Colorado geometry.
            mapView.setViewpointGeometry(coloradoGraphic.geometry!, padding: 100)
        }
    }

    // MARK: Instance properties

    /// A Boolean value indicating whether the geometries are clipped.
    private var geometriesAreClipped = false

    /// The unclipped graphic of Colorado.
    private var coloradoGraphic: AGSGraphic {
        coloradoGraphicsOverlay.graphics.firstObject as! AGSGraphic
    }

    /// The overlay for displaying the graphic of Colorado.
    private let coloradoGraphicsOverlay: AGSGraphicsOverlay = {
        // An envelope approximating the boundary of Colorado.
        let coloradoGeometry = AGSEnvelope(
            xMin: -11362327.128340,
            yMin: 5012861.290274,
            xMax: -12138232.018408,
            yMax: 4441198.773776,
            spatialReference: .webMercator()
        )

        // A semi-transparent blue color for the fill.
        let fillColor = UIColor.blue.withAlphaComponent(0.2)

        // The fill symbol for displaying Colorado.
        let fillSymbol = AGSSimpleFillSymbol(
            style: .solid,
            color: fillColor,
            outline: AGSSimpleLineSymbol(style: .solid, color: .blue, width: 2)
        )

        // Create a graphic from the geometry and symbol representing Colorado.
        let coloradoGraphic = AGSGraphic(geometry: coloradoGeometry, symbol: fillSymbol)

        // Create a graphics overlay.
        let coloradoGraphicsOverlay = AGSGraphicsOverlay()
        // Add the Colorado graphic to its overlay.
        coloradoGraphicsOverlay.graphics.add(coloradoGraphic)
        return coloradoGraphicsOverlay
    }()

    /// The graphics overlay containing clipped graphics.
    private let clippedGraphicsOverlay = AGSGraphicsOverlay()

    /// The overlay for displaying the other envelopes.
    private let envelopesGraphicsOverlay: AGSGraphicsOverlay = {
        // An envelope outside Colorado.
        let outsideEnvelope = AGSEnvelope(
            xMin: -11858344.321294,
            yMin: 5147942.225174,
            xMax: -12201990.219681,
            yMax: 5297071.577304,
            spatialReference: .webMercator()
        )

        // An envelope intersecting Colorado.
        let intersectingEnvelope = AGSEnvelope(
            xMin: -11962086.479298,
            yMin: 4566553.881363,
            xMax: -12260345.183558,
            yMax: 4332053.378376,
            spatialReference: .webMercator()
        )

        // An envelope inside Colorado.
        let containedEnvelope = AGSEnvelope(
            xMin: -11655182.595204,
            yMin: 4741618.772994,
            xMax: -11431488.567009,
            yMax: 4593570.068343,
            spatialReference: .webMercator()
        )

        // A dotted red outline symbol.
        let redOutline = AGSSimpleLineSymbol(style: .dot, color: .red, width: 3)

        // The envelopes in the order we want to display them.
        let envelopes = [outsideEnvelope, intersectingEnvelope, containedEnvelope]

        // The graphics for the envelopes with the red outline symbol.
        let graphics = envelopes.map { AGSGraphic(geometry: $0, symbol: redOutline) }

        let envelopesOverlay = AGSGraphicsOverlay()
        // Add the graphics to the overlay.
        envelopesOverlay.graphics.addObjects(from: graphics)
        return envelopesOverlay
    }()

    // MARK: Actions

    /// Clip geometries and add resulting graphics.
    private func clipGeometries() {
        // Hides the Colorado graphic.
        coloradoGraphic.isVisible = false

        let coloradoGeometry = coloradoGraphic.geometry!
        let coloradoSymbol = coloradoGraphic.symbol!

        // Clip Colorado's geometry to each envelope.
        let clippedGraphics: [AGSGraphic] = envelopesGraphicsOverlay.graphics.map { graphic in
            let envelope = (graphic as! AGSGraphic).geometry as! AGSEnvelope
            // Use the geometry engine to create a new geometry for the area of
            // Colorado that overlaps the given envelope.
            let clippedGeometry = AGSGeometryEngine.clipGeometry(coloradoGeometry, with: envelope)
            // Create and return the clipped graphic from the clipped geometry
            // if there is an overlap.
            return AGSGraphic(geometry: clippedGeometry, symbol: coloradoSymbol)
        }
        // Add the clipped graphics.
        clippedGraphicsOverlay.graphics.addObjects(from: clippedGraphics)
    }

    /// Remove all clipped graphics.
    private func reset() {
        clippedGraphicsOverlay.graphics.removeAllObjects()
        coloradoGraphic.isVisible = true
    }

    @IBAction func clipGeometry(_ sender: UIBarButtonItem) {
        geometriesAreClipped ? reset() : clipGeometries()
        geometriesAreClipped.toggle()
        // Set button title based on whether the geometries are clipped.
        sender.title = geometriesAreClipped ? "Reset" : "Clip"
    }

    // MARK: UIViewController

    override func viewDidLoad() {
        super.viewDidLoad()
        // Add the source code button item to the right of navigation bar.
        (navigationItem.rightBarButtonItem as! SourceCodeBarButtonItem).filenames = ["ClipGeometryViewController"]
    }
}

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