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Reverse Geocoding in QML

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[[Category:Qt Mobility]][[Category:Location]][[Category:Code Snippet]][[Category:Nokia Maps]]
[[Category:Qt Mobility]][[Category:Code Snippet]][[Category:Nokia Maps]]
{{ArticleMetaData <!-- v1.1 -->
{{ArticleMetaData <!-- v1.1 -->
|sourcecode= [[Media:mapqmlreversegeocode.zip]]  
|sourcecode= [[Media:mapqmlreversegeocode.zip]]  

Revision as of 12:26, 1 February 2012

Article Metadata
Code ExampleCompatibility
Created: mahbub_s60 (27 Jan 2012)
Last edited: jasfox (01 Feb 2012)


Geocoding is the process of finding associated geographic coordinates (often expressed as latitude and longitude) from other geographic data, such as street addresses, or zip codes (postal codes). With geographic coordinates the features can be mapped and entered into Geographic Information Systems, or the coordinates can be embedded into media such as digital photographs via geotagging. Reverse geocoding is the opposite: finding an associated textual location such as a street address, from geographic coordinates. In this article and code snippet, we explain how we can get address of a place by reverse geocoding with Nokia map.

How to get address from coordinate

We call reverseGeocode() method of QGeoSearchManager and pass the coordinate of the place that we are looking for. If we are interested to a place near by then we can use our device’s positioning system to get the current location and that can be passed to reverseGeocode() method as shown in the following snippet. geocodeFinished slot will be called when it has found the address.

QGeoSearchReply *reply = m_searchManager->reverseGeocode(m_geoCoordinate); 
QObject::connect(reply, SIGNAL(finished()), this,SLOT(geocodeFinished()));
QObject::connect(reply,SIGNAL(error(QGeoSearchReply::Error, QString)), this,SLOT(resultsError(QGeoSearchReply::Error, QString)));

geocodeFinished has been implemented in the following code.

void CLocationSource::geocodeFinished()
QGeoSearchReply* reply = static_cast<QGeoSearchReply *>(sender());
if (reply->error() != QGeoSearchReply::NoError) {
// Errors are handled in a different slot (resultsError)
QList<QGeoPlace> places = reply->places();
if (places.length() == 0)
// do something here
QGeoAddress address = places[0].address();
QString message = address.city() + ", " + address.country().toLower();
disconnect(reply, SIGNAL(finished()), this,SLOT(geocodeFinished()));
disconnect(reply,SIGNAL(error(QGeoSearchReply::Error, QString)), this,SLOT(resultsError(QGeoSearchReply::Error, QString)));

We need very thin QML code as most stuffs are done in Qt C++ side and that is brought to QML side by using qmlRegisterType() method.

        PositionSource {
id: apositionSource
updateInterval: 1000
active: false
// nmeaSource: "nmealog.txt"
id: positionSource
console.log(" onLonChanged in QML")
console.log(" onLatChanged in QML")
console.log(" Address has been changed")
id: mycordinate
latitude: positionSource.lat
longitude: positionSource.lon
id: map
plugin : Plugin { name : "nokia" }
anchors.fill: parent; size.width: parent.width; size.height: parent.height; zoomLevel: 12
center: mycordinate
Text {text: "Click on screen to swap positioningMethod: " }
Text {text: "<==== Position ====>"}
Text {text: "latitude: " + mycordinate.latitude}
Text {text: "longitude: " + mycordinate.longitude}
Text {text: "Address: " + positionSource.address}


Download the example for Symbian Belle: File:Mapqmlreversegeocode.zip

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