Marble/MarblePythonSignalsSlots

Basic interaction with MarbleWidget

Tutorial Series	Marble C++ Tutorial
Previous	[Projects/Marble/MarblePythonMarbleWidget
What's Next	Tutorial 4 - Loading KML files into MarbleWidget
Further Reading	n/a

Creating a window with controls

Quick Note: the documentation for the Marble Python bindings are currently not available online. They can instead be found in the source code at the location: src/bindings/python/html/marble/Marble.html.

We'd like to add other widgets to our Marble window: A zoom slider and a label that shows the current zoom level of the map.

In order to achieve this we need to create a vertical layout. The layout must be added as the central widget to the application, and have the map, slider and label added to it. Also we zoom the globe to the slider's default value using the MarbleWidget.zoomView(int) method.

We want to center our globe onto South America. So we create a new GeoDataCoordinates object that takes the longitude and the latitude as a parameter and we call MarbleWidget.centerOn(location).

As you might have realized already GeoDataCoordinates is the geodetic "sister" of QPoint. They share a very similar API. Additionally GeoDataCoordinates features a nice set of string conversion methods (GeoDataCoordinates.fromString(), GeoDataCoordinates.lonToString() and GeoDataCoordinates.latToString()). They are used in various places inside Marble such as the signal MarbleWidget.mouseMoveGeoPosition(string) .

Finally we connect the signals and slots that MarbleWidget offers to the signals and slots of the slider and the label (and the label, through a custom method that prefixes the string 'Zoom Level:'):

#!/usr/bin/env python
from PyQt4.QtCore import *
from PyQt4.QtGui import *
from PyKDE4.kdeui import *
from PyKDE4.kdecore import *
from PyKDE4.marble import *
import sys

class MainWin (KMainWindow):
    def __init__ (self, *args):
        KMainWindow.__init__ (self)
	# create the marble widget
        self.marble = Marble.MarbleWidget(self)
        
        # Load the OpenStreetMap map
        self.marble.setMapThemeId("earth/plain/plain.dgml")
        
        # Enable the cloud cover and enable the country borders
        self.marble.setShowClouds(True)
        self.marble.setShowBorders(True)
        
        # Hide the FloatItems: Compass and StatusBar
        self.marble.setShowOverviewMap(False)
        self.marble.setShowScaleBar(False)
        self.marble.setShowCompass(False)
      
        # Change the map to center on Australia
        home = Marble.GeoDataCoordinates(135.0, -25.0, 0.0, Marble.GeoDataCoordinates.Degree)
        self.marble.centerOn(home);
        
        # create the slider
        self.zoomSlider = QSlider(Qt.Horizontal)
        # set the limits of the slider
        self.zoomSlider.setMinimum(1000)
        self.zoomSlider.setMaximum(2400)
        # set a default zoom value
        self.zoomSlider.setValue(1200)
        
        # zoom 
        self.marble.zoomView(self.zoomSlider.value())
        
        # create the position label
        self.zoomLabel = QLabel()
        # show the current zoom level
        self.setZoomLabel(self.zoomSlider.value())
        
        # make elements size correctly
        self.zoomLabel.setSizePolicy(QSizePolicy.Preferred, QSizePolicy.Fixed)
        
        # create the layout
        self.layout_placeholder = QWidget()
        self.layout = QVBoxLayout()
        
        # add all the components
        self.layout.addWidget(self.marble)
        self.layout.addWidget(self.zoomSlider)
        self.layout.addWidget(self.zoomLabel)
        
        # add all the widgets to the layout placeholder
        self.layout_placeholder.setLayout(self.layout)
        # make the layout placeholder the central widget
        self.setCentralWidget(self.layout_placeholder)
        
        # connect slider value to map zoom via signal slots
        self.connect(self.zoomSlider, SIGNAL('valueChanged(int)'), self.marble.zoomView)
        
        # display the zoom level on the label, but pass it though the
        # custom self.setZoomLabel function to add prefix text
        self.connect(self.marble, SIGNAL('zoomChanged(int)'), self.setZoomLabel)
        
        # resize the window
        self.resize(600, 400)
        
        # display the app
        self.show()
    def setZoomLabel(self, value):
      self.zoomLabel.setText("Zoom Level: " + str(value))
        

def main():
    # defaults needed for the KApplication to be initialized
    appName     = "marble_map_widget_controls"
    catalog     = ""
    programName = ki18n ("Marble Map with Controls")
    version     = "1.0"
    description = ki18n ("Using Marble API to control map zoom with a slider.")
    license     = KAboutData.License_GPL
    copyright   = ki18n ("(c) 2008 Your Name")
    text        = ki18n ("none")
    homePage    = "www.example.com"
    bugEmail    = "[email protected]"

    aboutData   = KAboutData (appName, catalog, programName, version, description,
                              license, copyright, text, homePage, bugEmail)

    KCmdLineArgs.init(sys.argv, aboutData)
    
    app = KApplication()
    # initialize our window, which will call the MainWindow.__init__ function above
    mainWindow = MainWin(None, "main window")
    # quit the application when the last window closes
    app.connect(app, SIGNAL ("lastWindowClosed ()"), app.quit)
    # run the app
    app.exec_()

main()

Save the code above as marble_controls.py and run it:

python marble_controls.py

If things go fine, you end up with a map application that displays clouds on top of a flat map with clouds over it (you may need to zoom out):