HeatmapDensityBasedAlgorithm Class

The algorithm that allows the Map Control to plot a heatmap based on the density of heatmap points.

Assembly: DevExpress.Xpf.Map.v24.2.dll

Declaration

C#
VB.NET

public class HeatmapDensityBasedAlgorithm :
    HeatmapAlgorithmBase,
    IDensityBasedAlgorithm,
    IHeatmapAlgorithm

Public Class HeatmapDensityBasedAlgorithm
    Inherits HeatmapAlgorithmBase
    Implements IDensityBasedAlgorithm,
               IHeatmapAlgorithm

Remarks

When you use the HeatmapDensityBasedAlgorithm to create a heatmap, the Map Control aggregates points into areas of different colors. An area with high point density is painted red. A green area indicates that this region contains a low number of points. The Map Control re-aggregates heatmap points when you zoom in/out of a map. For this reason, areas of aggregated points can change their colors.

To change the predefined color scheme, specify the HeatmapProvider.Colorizer property. The first item in the ChoroplethColorizer.Colors collection defines a color for areas with low point density, the last item specifies the color of areas with high point density.

Example

This example shows how to create a heatmap layer for the Map Control.

Create an ImageLayer object and add it to the MapControl.Layers collection.
Assign a HeatmapProvider object to the ImageLayer.DataProvider property.

Markup

XAML

<Window
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Heatmap"
        xmlns:dxm="http://schemas.devexpress.com/winfx/2008/xaml/map" 
        x:Class="Heatmap.MainWindow"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Window.DataContext>
        <local:EarthquakesData/>
    </Window.DataContext>
    <Grid>
        <dxm:MapControl ZoomLevel="2">
            <dxm:ImageLayer>
                <dxm:BingMapDataProvider BingKey="Your Bing Maps key here."/>
            </dxm:ImageLayer>
            <!-- The heatmap layer configuration -->
            <dxm:ImageLayer Name="heatmapLayer" Opacity="0.75">
                <dxm:HeatmapProvider>
                    <dxm:HeatmapProvider.Colorizer>
                        <dxm:ChoroplethColorizer RangeStops="0.1, 0.2, 0.7, 1.0" 
                                                 ApproximateColors="True">
                            <dxm:ChoroplethColorizer.Colors>
                                <Color A="50"  R="128"  G="255"  B="0"/>
                                <Color A="255" R="255"  G="255"  B="0"/>
                                <Color A="255" R="234"  G="72"   B="58"/>
                                <Color A="255" R="162"  G="36"   B="25"/>
                            </dxm:ChoroplethColorizer.Colors>
                        </dxm:ChoroplethColorizer>
                    </dxm:HeatmapProvider.Colorizer>
                    <dxm:HeatmapProvider.PointSource>
                        <dxm:HeatmapDataSourceAdapter DataSource="{Binding Path=DataItems}">
                            <dxm:HeatmapDataSourceAdapter.Mappings>
                                <dxm:HeatmapPointMappingInfo XCoordinate="Longitude" 
                                                             YCoordinate="Latitude"/>
                            </dxm:HeatmapDataSourceAdapter.Mappings>
                        </dxm:HeatmapDataSourceAdapter>
                    </dxm:HeatmapProvider.PointSource>
                    <dxm:HeatmapProvider.Algorithm>
                        <dxm:HeatmapDensityBasedAlgorithm PointRadius="10"/>
                    </dxm:HeatmapProvider.Algorithm>
                </dxm:HeatmapProvider>
            </dxm:ImageLayer>
            <!--...-->
        </dxm:MapControl>
    </Grid>
</Window>

Code-Behind

C#
VB.NET

using System;
using System.Collections.Generic;
using System.IO;
using System.Windows;
using System.Xml.Serialization;
namespace Heatmap {
    public partial class MainWindow : Window {
        public MainWindow() {
            InitializeComponent();
        }
    }
    public class EarthquakeViewModel {
        [XmlElement("glat")]
        public double Latitude { get; set; }
        [XmlElement("glon")]
        public double Longitude { get; set; }
    }
    [XmlRoot("Data")]
    public class EarthquakesData {
        static EarthquakesData instance;
        public static List<EarthquakeViewModel> DataItems {
            get { return Instance.Items; }
        }
        public static EarthquakesData Instance {
            get { return instance ?? (instance = CreateInstance()); }
        }
        static EarthquakesData CreateInstance() {
            XmlSerializer serializer = new XmlSerializer(typeof(EarthquakesData));
            Stream documentStream = LoadStreamFromResources("/Data/Earthquakes.xml");
            return (EarthquakesData)serializer.Deserialize(documentStream);
        }
        [XmlElement("Row")]
        public List<EarthquakeViewModel> Items { get; set; }
        public static Stream LoadStreamFromResources(string fileName) {
            try {
                Uri uri = new Uri(fileName, UriKind.RelativeOrAbsolute);
                return Application.GetResourceStream(uri).Stream;
            }
            catch {
                return null;
            }
        }
    }
}

Imports System
Imports System.Collections.Generic
Imports System.IO
Imports System.Windows
Imports System.Xml.Serialization
Namespace Heatmap
    Public Partial Class MainWindow
        Inherits Window
        Public Sub New()
            InitializeComponent()
        End Sub
    End Class
    Public Class EarthquakeViewModel
        <XmlElement("glat")>
        Public Property Latitude As Double
        <XmlElement("glon")>
        Public Property Longitude As Double
    End Class
    <XmlRoot("Data")>
    Public Class EarthquakesData
        Shared instance As EarthquakesData
        Public Shared ReadOnly Property DataItems As List(Of EarthquakeViewModel)
            Get
                Return Instance.Items
            End Get
        End Property
        Public Shared ReadOnly Property Instance As EarthquakesData
            Get
                Return If(instance, (CSharpImpl.__Assign(instance, CreateInstance())))
            End Get
        End Property
        Private Shared Function CreateInstance() As EarthquakesData
            Dim serializer As XmlSerializer = New XmlSerializer(GetType(EarthquakesData))
            Dim documentStream As Stream = LoadStreamFromResources("/Data/Earthquakes.xml")
            Return CType(serializer.Deserialize(documentStream), EarthquakesData)
        End Function
        <XmlElement("Row")>
        Public Property Items As List(Of EarthquakeViewModel)
        Public Shared Function LoadStreamFromResources(ByVal fileName As String) As Stream
            Try
                Dim uri As Uri = New Uri(fileName, UriKind.RelativeOrAbsolute)
                Return Application.GetResourceStream(uri).Stream
            Catch
                Return Nothing
            End Try
        End Function
        Private Class CSharpImpl
            Shared Function __Assign(Of T)(ByRef target As T, value As T) As T
                target = value
                Return value
            End Function
        End Class
    End Class
End Namespace