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ArcGIS Runtime SDK for Qt

Buffer

Sample Viewer View Sample on GitHub

Create a buffer around a map point and display the results as a Graphic.

Use case

Creating buffers is a core concept in GIS proximity analysis that allows you to visualize and locate geographic features contained within a polygon. For example, suppose you wanted to visualize areas of your city where alcohol sales are prohibited because they are within 500 meters of a school. The first step in this proximity analysis would be to generate 500 meter buffer polygons around all schools in the city. Any such businesses you find inside one of the resulting polygons are violating the law.

How to use the sample

  1. Tap on the map.
  2. A planar and a geodesic buffer will be created at the tap location using the distance (miles) specified in the text box.
  3. Continue tapping to create additional buffers. Notice that buffers closer to the equator appear similar in size. As you move north or south from the equator, however, the geodesic polygons become much larger. Geodesic polygons are in fact a better representation of the true shape and size of the buffer.
  4. Click Clear to remove all buffers and start again.

How it works

  1. The map Point for a tap on the display is captured.
  2. The static method GeometryEngine.buffer is called to create a planar buffer polygon from the map location and distance.
  3. Another static method, GeometryEngine.bufferGeodetic is called to create a geodesic buffer polygon using the same inputs.
  4. The polygon results (and tap location) are displayed in the map view with different symbols in order to highlight the difference between the buffer techniques due to the spatial reference used in the planar calculation.

Relevant API

  • GeometryEngine.buffer
  • GeometryEngine.bufferGeodetic
  • GraphicsOverlay

Additional information

Buffers can be generated as either planar (flat - coordinate space of the map's spatial reference) or geodesic (technique that considers the curved shape of the Earth's surface, which is generally a more accurate representation). In general, distortion in the map increases as you move away from the standard parallels of the spatial reference's projection. This map is in Web Mercator so areas near the equator are the most accurate. As you move the buffer location north or south from that line, you'll see a greater difference in the polygon size and shape. Planar operations are generally faster, but performance improvement may only be noticeable for large operations (buffering a great number or complex geometry).

For more information about using buffer analysis, see the topic How Buffer (Analysis) works in the ArcGIS Pro documentation.

Tags

analysis, buffer, euclidean, geodesic, geometry, planar

Sample Code

import QtQuick 2.6
import QtQuick.Controls 2.2
import Esri.ArcGISRuntime 100.9

Rectangle {
    id: rootRectangle
    clip: true
    width: 800
    height: 600

    

    // declare a map view
    MapView {
        id: mapView
        anchors.fill: parent

        // Add a map with a basemap
        Map {
            BasemapTopographic {}
        }

        // handle the mouse click - perform a buffer on click
        onMouseClicked: bufferPoint(mouse.mapPoint);

        // create graphics overlay for geodesic buffer graphics
        GraphicsOverlay {
            id: graphicsOverlaygeodesic

            // Set the renderer
            SimpleRenderer {
                // create a simple fill symbol for the geodesic buffer result
                SimpleFillSymbol {
                    id: geodesicBufferSymbol
                    color: Qt.rgba(1, 0, 0, 0.5)
                    style: Enums.SimpleFillSymbolStyleSolid

                    SimpleLineSymbol {
                        color: geodesicBufferSymbol.color
                        style: Enums.SimpleLineSymbolStyleSolid
                        width: 2
                    }
                }
            }
        }

        // create graphics overlay for planar buffer graphics
        GraphicsOverlay {
            id: graphicsOverlayPlanar

            // Set the renderer
            SimpleRenderer {
                // create a simple fill symbol for the planar buffer result
                SimpleFillSymbol {
                    id: planarBufferSymbol
                    color: Qt.rgba(0, 0, 1, 0.5)
                    style: Enums.SimpleFillSymbolStyleSolid

                    SimpleLineSymbol {
                        color: planarBufferSymbol.color
                        style: Enums.SimpleLineSymbolStyleSolid
                        width: 2
                    }
                }
            }
        }

        // create graphics overlay for the mouse clicks
        GraphicsOverlay {
            id: graphicsOverlayPoints

            // Set the renderer
            SimpleRenderer {
                // create a marker symbol for the clicked point
                SimpleMarkerSymbol {
                    id: pointSymbol
                    color: "white"
                    size: 14
                    style: Enums.SimpleMarkerSymbolStyleCross
                }
            }
        }
    }

    // function to buffer a point and add graphics
    function bufferPoint(point) {
        // Create a variable to be the buffer size in meters. There are 1609.34 meters in one mile.
        const bufferInMeters = bufferSizeText.text * 1609.34;

        // Create a planar buffer graphic around the input location at the specified distance.
        const buffer = GeometryEngine.buffer(point, bufferInMeters);

        // Add the result planar buffer as a graphic
        const resultGraphic = ArcGISRuntimeEnvironment.createObject("Graphic", {
                                                                        geometry: buffer
                                                                    });
        graphicsOverlayPlanar.graphics.append(resultGraphic);

        // Create a geodesic buffer graphic using the same location and distance.
        const bufferGeodesic = GeometryEngine.bufferGeodetic(point, bufferInMeters, Enums.LinearUnitIdMeters, NaN, Enums.geodesicCurveTypeGeodesic);

        // Add the result planar buffer as a graphic
        const resultGraphicGeodesic = ArcGISRuntimeEnvironment.createObject("Graphic", {
                                                                                geometry: bufferGeodesic
                                                                            });
        graphicsOverlaygeodesic.graphics.append(resultGraphicGeodesic);

        // Add the clicked point as a graphic
        const clickedPointGraphic = ArcGISRuntimeEnvironment.createObject("Graphic", {
                                                                              geometry: point
                                                                          });
        graphicsOverlayPoints.graphics.append(clickedPointGraphic);
    }

    // display a control pane to change size
    Rectangle {
        anchors {
            margins: -5
            fill: controlColumn
        }
        color: "lightgray"
        radius: 5
        border {
            color: "darkgray"
            width: 1
        }
    }

    Column {
        id: controlColumn
        anchors {
            left: parent.left
            top: parent.top
            margins: 10
        }
        spacing: 5

        Text {
            text: "Buffer size (miles):"
        }

        TextField {
            id: bufferSizeText
            validator: IntValidator { bottom: 1; top: 10000 }
            text: "1000"
            selectByMouse: true
        }

        Row {
            spacing: 10

            Rectangle {
                radius: 100
                width: 15
                height: width
                color: planarBufferSymbol.color
            }

            Text {
                text: "Planar Buffer"
            }
        }

        Row {
            spacing: 10

            Rectangle {
                radius: 100
                width: 15
                height: width
                color: geodesicBufferSymbol.color
            }

            Text {
                text: "Geodesic Buffer"
            }
        }

        Button {
            anchors.horizontalCenter: parent.horizontalCenter
            text: "Clear"
            onClicked: {
                graphicsOverlaygeodesic.graphics.clear();
                graphicsOverlayPlanar.graphics.clear();
                graphicsOverlayPoints.graphics.clear();
            }
        }
    }
}