GAMBAS BOOK 3.19.1

The free map material from openstreetmap.org (OSM) is used for the two projects presented. In a displayed map - shown in a MapView - you can zoom the map section in 18 steps with the mouse wheel and move the displayed map area with a permanent click on the map.

There are three prerequisites for displaying a map:

• Accurate knowledge of the geographic coordinates of the location on Earth to be displayed - preferably as latitude and longitude in decimal degrees.
• Selection of a suitable zoom factor from the interval [1..18], which determines the size of the map section.
• Active internet connection to retrieve the (pre-)calculated maps from the server.

The presented project implements a viewer for maps from OSM.

Figure 24.8.1.2.1: GeoMap1 - Hanseatic City Osterburg in Saxony/Anhalt

The source code for the project is given in full:

[1] ' Gambas class file
[2]
[3] Public Sub Form_Open()
[4]   FMain.Center
[5]   FMain.Caption = "GeoMap - Daten von OpenStreetMap"
[6]   btnHelp.Value = True
[7]   ShowMap()
[8] End ' Form_Open()
[9]
[10] Public Sub ShowMap()
[11]   Dim iZoom As Integer
[12]   Dim fLatitude, fLongitude As Float
[13]   Dim sCacheName, sTileName, sTilePattern As String
[14]   Dim cArguments As New Collection
[15]
[16] ' Initialisierung
[17]   iZoom = 13
[18]   sTileName = "OpenStreetMap"
[19]   sTilePattern = "85.30.190.241/{z}/{x}/{y}.png"
[20]   cArguments = Null
[21]   sCacheName = Null
[22]   fLatitude = 52.7905  ' °Breite Osterburg
[23]   fLongitude = 11.7531 ' °Länge Osterburg
[24]
[25]   MapView1.Map.AddTile(sTileName, sTilePattern, cArguments, sCacheName)
[26]   MapView1.Map[sTileName].Copyright = " © OpenStreetMap"
[27]   MapView1.Map[sTileName].Visible = True ' optional; Standard-Einstellung ist TRUE
[28]   MapView1.Map.AddShape("P1")
[29]   MapView1.Map!P1.AddPoint("Osterburg", MapPoint(fLatitude, fLongitude))
[30]   MapView1.Map.Center = MapPoint(fLatitude, fLongitude)
[31] ' MapView1.Map.Center = MapView1.Map!P1!Osterburg.Points ' Alternative
[32]   MapView1.Map.Zoom = iZoom
[33]   MapView1.AllowEffect = True
[34] End ' ShowMap()
[35]
[36] Public Sub btnHelp_Click()
[37]   ShowHelp()
[38] End ' btnHelp_Click()
[39]
[40] Public Sub ShowHelp()
[41]   Dim sMessage As String
[42]
[43]   sMessage = "<hr><b>Hinweise zum Einsatz der Komponente Map</b><hr>"
[44]   sMessage &= "» Verschieben der Karte mit gedrückter linker Maustaste<br>"
[45]   sMessage &= "» Zoomen mit dem Maus-Rad<br>"
[46]   sMessage &= "» Zoomen mit dem Schieberegler<hr>"
[47]   sMessage &= "» Die Tastenkombination ALT+B beendet das Programm<hr>"
[48]   sMessage &= "▪ Entwickler der Komponente <i>gb.map</i>  ist Fabien Bodard"
[49]   sMessage &= "<br>▪ EMail: gambix@users.sourceforge.net<hr>"
[50]   Message.Info(sMessage)
[51] End ' ShowHelp()
[52]
[53] Public Sub btnClose_Click()
[54]   FMain.Close
[55] End ' btnClose_Click()

Notes:

• In line 19, the adequate IP address is used instead of the URL {s}.tile.openstreetmap.org. This is only advantageous if there are problems with the DNS server in connection with intermediary routers.<x ul>*</x> If you want to print out the displayed map - a corresponding class for this is being developed by F. Bodard - or use it in another context, then you must display a copyright notice on the map in line 26 in order to comply with the licence conditions! * The map tiles are stored in the directory ~/.cache/gb.map/MyMapCache/.
• For detailed information on the arguments and the cache, see the documentation.

Help is displayed when the programme is started:

Figure 24.8.1.2.2: Programme Help

The second project is an adaptation of the MapView programme example by Fabien Bodard - the developer of the Map component - from the Gambas sample collection.

In addition to displaying a map, you can switch on a magnifying glass function with the CTRL key:

Figure 24.8.1.3.1: GeoMap2 with magnifying glass

The archives for both projects are in the download directory.