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Revision as of 04:23, 11 October 2012 by hamishwillee (Talk | contribs)

Reverse Geocoding in QML

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Platform(s):
Symbian
Article
Created: mahbub_s60 (27 Jan 2012)
Last edited: hamishwillee (11 Oct 2012)


Introduction

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)
return;
}
 
QList<QGeoPlace> places = reply->places();
if (places.length() == 0)
{
 
// do something here
}
else
{
QGeoAddress address = places[0].address();
QString message = address.city() + ", " + address.country().toLower();
setAddress(message);
}
 
disconnect(reply, SIGNAL(finished()), this,SLOT(geocodeFinished()));
disconnect(reply,SIGNAL(error(QGeoSearchReply::Error, QString)), this,SLOT(resultsError(QGeoSearchReply::Error, QString)));
reply->deleteLater();
}

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"
}
CLocationSource
{
id: positionSource
onLonChanged:
{
console.log(" onLonChanged in QML")
}
onLatChanged:
{
console.log(" onLatChanged in QML")
}
onAddressChanged:
{
console.log(" Address has been changed")
}
}
 
Coordinate
{
id: mycordinate
latitude: positionSource.lat
longitude: positionSource.lon
}
 
Map
{
id: map
plugin : Plugin { name : "nokia" }
anchors.fill: parent; size.width: parent.width; size.height: parent.height; zoomLevel: 12
center: mycordinate
 
}
Column
{
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}
}

Examples

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

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