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WPF Map Control using openstreetmap.org Data

, 15 Jun 2010 CPOL
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A WPF control that displays data from OpenStreetMap
This is an old version of the currently published article.
MapControl.png

Introduction

This article will create a simple WPF control that enables browsing of map data from OpenStreetMap, as well as enabling searching for places and displaying the results on the map.

The attached zip file has both the source code, with documentation, and a sample application.

Background

I needed to allow the user to select various locations in my project but didn't want the user to have to install any other applications (such as Google Earth or Bing Maps 3D). One option was to have a web browser in my application pointing to the online versions, but this didn't feel right. Finally I looked at OpenStreetMap and was impressed by the maps, but couldn't find any controls to put it in my application.

What is OpenStreetMap?

From their Main Wiki page:

OpenStreetMap creates and provides free geographic data such as street maps to anyone who wants them. The project was started because most maps you think of as free actually have legal or technical restrictions on their use, holding back people from using them in creative, productive, or unexpected ways.

Basically, OpenStreetMap is a map made by the community for everybody to use. Also, luckily for me, all the details for the file naming conventions are there for creating our own control. All we have to do is download the relevant 256 x 256 pixel square image tiles for the area we want to look at and stitch them together - simple!

Performance

The WPF Image control takes care of the downloading work automatically for us, however, performance wouldn't be great if we had to download the same tiles again and again so, naturally, they will be downloaded once and cached to the local hard drive. However, I noticed that when loading the images from the hard drive, there was a slight delay (even when setting the BitmapImage.CreateOptions to DelayCreation). Although the delay is small for each tile, because there are lots of tiles, the delay adds up and the UI becomes unresponsive.

At first, I found this excellent article that enabled the control to be on a separate thread to the rest of the application. It instantly solved the UI updating problems perfectly. However, even though the tiles were being loaded on another thread, the control would not update its visual until all the tiles had finished updating. My spidey sense was telling me I could play around with the Dispatcher to force an update and after a quick look at MSDN, I found a replacement for the Windows Forms DoEvents method. Therefore, I abandoned the multi-threaded visual and simply called DoEvents() before updating each row.

Using the Code

All the basic functionality for displaying a map and searching is in the MapControl project, however, you will need to create the controls for navigating and for getting the search query from the user. I've made a separate project called SampleApp which does just this, but I must confess my design skills suck.

TileGenerator Class

This class has helper methods to retrieve information from OpenStreetMap and has the following members:

public static class TileGenerator
{
    // The maximum allowed zoom level.
    public const int MaxZoom = 18;

    // Occurs when the download progress of a tile image has changed.
    public static event EventHandler<system.windows.media.imaging.downloadprogresseventargs /> ImageDownloadingProgress;

    // Gets or sets the folder used to store the downloaded tiles.
    public static string CacheFolder { get; set; }

    // Gets the number of tile images waiting to be downloaded.
    // Note: this is not the same as the number of active downloads.
    public static int DownloadCount { get; }

    // Returns a valid value for the specified zoom, 
    // in the range of 0 - MaxZoom inclusive.
    public static int GetValidZoom(int zoom);
}

Before we do anything with any of the map controls, even before trying to call their constructors, we need to set the directory for the tile image cache folder. Here MainWindow is assumed to be the first window loaded but you could instead put this line inside the constructor of the default App class:

public MainWindow()
{
    // Very important we set the CacheFolder before doing anything 
    // so the MapCanvas knows where
    // to save the downloaded files to.
    TileGenerator.CacheFolder = @"ImageCache";

    this.InitializeComponent(); 	// Because this will create the MapCanvas, 
				// it has to go after the above.
}

MapCanvas Class

The actual map is displayed inside the MapCanvas, which is inherited from the WPF Canvas control (hence the well thought out name Wink | ;) ).

public sealed class MapCanvas : Canvas
{
    // Identifies the Latitude attached property.
    public static readonly DependencyProperty LatitudeProperty;

    // Identifies the Longitude attached property.
    public static readonly DependencyProperty LongitudeProperty;

    // Identifies the Viewport dependency property. This will be read only.
    public static readonly DependencyProperty ViewportProperty;

    // Identifies the Zoom dependency property.
    public static readonly DependencyProperty ZoomProperty;

    // Gets the visible area of the map in latitude/longitude coordinates.
    public Rect Viewport { get; }

    // Gets or sets the zoom level of the map.
    public int Zoom { get; set; }

    // Gets the value of the Latitude attached property for a given dependency object.
    public static double GetLatitude(DependencyObject obj);

    // Gets the value of the Longitude attached property for a given dependency object.
    public static double GetLongitude(DependencyObject obj);

    // Sets the value of the Latitude attached property for a given dependency object.
    public static void SetLatitude(DependencyObject obj, double value);

    // Sets the value of the Longitude attached property for a given dependency object.
    public static void SetLongitude(DependencyObject obj, double value);

    // Centers the map on the specified coordinates, calculating the required zoom level.
    // The size parameter is the minimum size that must be visible, 
    // centered on the coordinates.
    // i.e. the longitude range that must be visible will be: 
    // longitude +- (size.Width / 2)
    public void Center(double latitude, double longitude, Size size);

    // Creates a static image of the current view.
    public ImageSource CreateImage();

    // Calculates the coordinates of the specified point.
    // The point should be in pixels, relative to the top left corner of the control.
    // The returned Point will be filled with the Latitude in the Y property and
    // the Longitude in the X property.
    public Point GetLocation(Point point);
}

The main points of interest are the two attached properties that make it a bit easier for positioning child controls (though you can still use the regular Canvas ones such as Canvas.Left, etc.): MapCanvas.Latitude and MapCanvas.Longitude. Using them should be straight forward:

<!--<span class="code-comment"> Make sure you've included a reference to MapControl.dll in your project --></span>
<!--<span class="code-comment"> and put a reference like the following at the start of the XAML file: --></span>
<!--<span class="code-comment"> xmlns:map="clr-namespace:MapControl;assembly=MapControl" --></span>

<map:MapCanvas>
  <!--<span class="code-comment"> The Top Left corner of the control will be at the specified Latitude + Longitude,
  so set a negative Margin to centralise the control on the coordinates. --></span>
  <Rectangle Fill="Red" Height="50" Width="50" Margin="-25,-25,0,0"
             map:MapCanvas.Latitude="38.895" map:MapCanvas.Longitude="-77.037" />
</map:MapCanvas>

Panning and Zooming

The MapCanvas will handle dragging with the mouse and zooming using the scroll wheel, however, you will probably want to add a set of navigation controls as well. To enable this, the MapControl registers itself with the following (self explanatory) standard WPF commands:

  • ComponentCommands.MoveDown
  • ComponentCommands.MoveLeft
  • ComponentCommands.MoveRight
  • ComponentCommands.MoveUp
  • NavigationCommands.DecreaseZoom
  • NavigationCommands.IncreaseZoom

SearchProvider/SearchResult Classes

This SearchProvider class first tries to parse the query for a decimal latitude and longitude (in that order, separated by a comma and/or space) but if that fails will pass the query on to Nominatim to search osm data by name and address. Just to reiterate, it will only try and parse decimal degrees, not degrees minutes seconds.

public sealed class SearchProvider
{
    // Occurs when the search has completed.
    public event EventHandler SearchCompleted;

    // Occurs if there were errors during the search.
    public event EventHandler<searcherroreventargs /> SearchError;

    // Gets the results returned from the most recent search.
    public SearchResult[] Results { get; }

    // Searches for the specified query, localizing the results to the specified area.
    // Note that it only returns true if a search was started. This does not always mean
    // that the method has failed - if a set of valid coordinates were passed as the query
    // then no search will be performed (returning false) but the SearchCompleted
    // event will be raised and the Results will be updated.
    public bool Search(string query, Rect area);
}

This finally leaves the SearchResult class that, as you would expect, contains information for an individual search result returned from Nominatim.

public sealed class SearchResult
{
    // Gets the formatted name of the search result.
    public string DisplayName { get; }

    // Gets the index the result was returned from the search.
    public int Index { get; }

    // Gets the latitude coordinate of the center of the search result.
    public double Latitude { get; }

    // Gets the longitude coordinate of the center of the search result.
    public double Longitude { get; }

    // Gets the size of the search's bounding box.
    public System.Windows.Size Size { get; }
}

Points of Interest

Before using the code or sample application, you should read and make sure you comply with the following:

The way I read it is make sure you put a copyright notice on the map (like the one in the bottom right hand corner of the sample application) and make sure you don't abuse the servers by downloading too much (such as trying to download all the tiles in one go).

History

  • 15/06/10 - Initial version

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Samuel Cragg
United Kingdom United Kingdom
No Biography provided

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Comments and Discussions


Discussions posted for the Published version of this article. Posting a message here will take you to the publicly available article in order to continue your conversation in public.
 
QuestionHow draw the line on the map Pin
dima__16-Jun-16 2:40
memberdima__16-Jun-16 2:40 
QuestionWPF Project issue Pin
adeshtalakane6-Jun-16 0:43
memberadeshtalakane6-Jun-16 0:43 
QuestionRemove panning functionality Pin
Member 103705118-Jan-16 0:25
memberMember 103705118-Jan-16 0:25 
QuestionAdding lines Pin
SeattleHeather18-Sep-15 10:57
memberSeattleHeather18-Sep-15 10:57 
SuggestionUsing other tile providers Pin
Richard V Williams3-Sep-15 23:29
memberRichard V Williams3-Sep-15 23:29 
Questionaddition Pin
Member 103265141-Jul-15 19:29
professionalMember 103265141-Jul-15 19:29 
QuestionIs possible to add an map overlay? Pin
Member 113769755-Feb-15 1:51
memberMember 113769755-Feb-15 1:51 
QuestionGreat Job!!!! Pin
raananv8-Dec-14 17:31
memberraananv8-Dec-14 17:31 
QuestionWorks a charm - thanks!! Pin
Paul Rahme7-Jul-14 23:45
memberPaul Rahme7-Jul-14 23:45 
QuestionGet Coordinates on mouse click Pin
boki_thegame19-May-14 10:09
memberboki_thegame19-May-14 10:09 

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