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Reverse Geocoding

In this guide you will learn how to use SearchService to perform a reverse geocoding search to find the positions of points of interest (POIs) near a programmatically or interactively/visually specified position on the map.

See the Search Example guide on how to perform an assisted address search.

See the Text Search guide on how to search for anything on the map with a free-form text query.

Get the Coordinates of a Point

QML reverse geocoding example

First, get an API key token, see the Getting Started guide.

Qt should be installed to continue.

The Maps SDK for Qt should be installed, see the Setup Maps SDK for Qt guide.

Overview

ReverseGeocoding demonstrates how to use SearchService to perform reverse geocoding. This example presents an application window displaying a list on the left and a map on the right.

QML reverse geocoding example

Clicking on the map will trigger a reverse geocoding search on that spot and the results will be displayed in the list on the left.

QML reverse geocoding example

How it works

In Qt, go to the File menu and select Open File or Project…

QML reverse geocoding example

then browse to the ReverseGeocoding example folder and open ReverseGeocoding.pro

You may want to have a look at Setting your API Key to see how to open and configure a project and set your API Key.

In main.qml, we import the GeneralMagic QML plugin. Next, we need to make sure we allow online access, and that we are using the latest data.

 1import QtQuick.Window 2.12
 2import GeneralMagic 2.0
 3
 4Window
 5{
 6  visible: true
 7  width: 640
 8  height: 480
 9  title: qsTr("Reverse Geocoding Example")
10  Component.onCompleted:
11  {
12    ServicesManager.settings.token = __my_secret_token;
13
14    ServicesManager.settings.allowInternetConnection = true;
15
16    var updater = ServicesManager.contentUpdater(ContentItem.Type.RoadMap);
17    updater.autoApplyWhenReady = true;
18    updater.update();
19  }

The __my_secret_token property in the above QML code is set in C++ like this.

1// C++ code
2QQmlApplicationEngine engine;
3//...
4//! [Set API Key token safely]
5// go to https://developer.generalmagic.com to get your token
6engine.rootContext()->setContextProperty("__my_secret_token", "YOUR_TOKEN");
7//! [Set API Key token safely]
8
9engine.load(url);

In this example, in main.cpp, replace YOUR_TOKEN with your actual General Magic Maps API Key.

We need to declare a SearchService model to perform the reverse geocoding search.

 1SearchService
 2{
 3  id: reverseGeocoding
 4  preferences
 5  {
 6    searchMapPOIs: true
 7    searchAddresses: true
 8    limit: 10
 9    thresholdDistance: 500
10  }
11}

On the left we have a ListView where we show the results of the reverse geocoding search.

 1ListView
 2{
 3  id: searchList
 4  anchors.fill: parent
 5  anchors.margins: 15
 6  clip: true
 7  model: reverseGeocoding
 8  function distance(meters)
 9  {
10    return meters >= 1000 ? (meters / 1000.).toFixed(3)
11    + " Km" :  meters.toFixed(0) + " m";
12  }
13  delegate: Item
14  {
15    height: row.height
16    RowLayout
17    {
18      id: row
19      IconView
20      {
21        iconSource: landmark.icon
22        Layout.maximumHeight: row.height
23        Layout.maximumWidth: row.height
24        width: height
25        height: row.height
26      }
27      ColumnLayout
28      {
29        Layout.fillHeight: true
30        Layout.fillWidth: true
31        Text
32        {
33          Layout.fillWidth: true
34          text: landmark.name + " (" + searchList.distance(
35            landmark.coordinates.distance(reverseGeocoding.coordinates)) + ")"
36          color: "white"
37          font.pixelSize: 16
38          wrapMode: Text.WrapAnywhere
39        }
40        Text
41        {
42          Layout.fillWidth: true
43          text: landmark.description
44          color: "white"
45          font.pixelSize: 14
46          font.italic: true
47          wrapMode: Text.WrapAnywhere
48        }
49      }
50    }
51  }
52}

On the right we have a simple map, and when we click on it we are using SearchService::reverseGeocode

1MapView
2{
3  id: mapView
4  Layout.fillWidth: true
5  Layout.fillHeight: true
6  gesturesEnabled: true
7  onCursorPositionChanged: reverseGeocoding.reverseGeocode(
8    mapView.cursorWgsPosition());
9}

QML Examples

Maps SDK for Qt Examples can be downloaded or cloned with Git