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HeatmapDensityBasedAlgorithm Class

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

Namespace: DevExpress.Xpf.Map

Assembly: DevExpress.Xpf.Map.v19.2.dll

Declaration

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.

Examples

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

Markup

<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

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;
            }
        }
    }
}
See Also