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Revision as of 13:55, 4 January 2013 by jasfox (Talk | contribs)

HERE Maps API - Converting a map screen pixel to a geo coordinate

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This article explains how to convert a map screen's pixel to a geocoordinate. This is useful when we want to know the geocoordinates of the point user had clicked.

Article Metadata
Tested with
Devices(s): Google Chrome, Mozilla Firefox, Internet Explorer, Opera
Compatibility
Platform(s): Web browser
Dependencies: Nokia Maps 2.2.3
Article
Keywords: Nokia Maps, JavaScript, Geocoordinates, onclick
Created: Maveric (21 Jun 2011)
Updated: avnee.nathani (06 Jan 2012)
Last edited: jasfox (04 Jan 2013)

Contents

Prerequisites

Nokia Maps API supported web browser (basically any modern web browser). The example assumes you have already added the Nokia Maps to your web page as explained in the previous article Nokia Maps API - Add Maps To Any Web Page

Important note about maps credentials

Nokia provides several services options within the Maps API offering. The service is free to use, but you must obtain and use authentication and authorization credentials to use the services. Please read the Terms and Conditions and check the Pricing Plans page to decide which business model best fits your needs. Authentication requires unique Maps API credentials, namely an AppId and a token. You can get these credentials free for free following the instructions here

Implementation

To achieve what we are about to do, we will need to use a method called pixelToGeo(), definition below:

pixelToGeo (coord) : nokia.maps.geo.Coordinate - this will translate a projected pixel coordinate into a GEO Coordinate.

We also need to use the EventListener() and addListener() method, which is defined by the Nokia Maps API reference as follows: addListener (type, listener, useCapture) ObjectRegisters an event listener, depending on the useCapture parameter, on the capture phase of the event flow or its target and bubbling phases.

Parameters: {String} type Specifies the event type associated with the event for which the user is registering. {Function} listener The function to be called if the event occurs.

Example code

This example will add a new eventListener on the map and register the "click" event to fire the function eventListener(). We will get the position user had clicked and this will be converted from a pixel projection coordinate to a geo.Coordinate. The result is sent to screen with JavaScript Alert() method.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Pixel to geocoordinate</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<script type="text/javascript"
src="http://api.maps.nokia.com/2.2.3/jsl.js" charset="utf-8">
</script>
</head>
<body>
 
<div id="mapContainer" style="z-index: -1; left:0px; top:0px; width: 100%; height: 80%; position: absolute;"></div>
<script type="text/javascript">
/////////////////////////////////////////////////////////////////////////////////////
// Don't forget to set your API credentials
//
// Replace with your appId and token which you can obtain when you
// register on http://api.developer.nokia.com/
//
nokia.Settings.set( "appId", "YOUR APP ID GOES HERE");
nokia.Settings.set( "authenticationToken", "YOUR AUTHENTICATION TOKEN GOES HERE");
 
//
/////////////////////////////////////////////////////////////////////////////////////
var map = new nokia.maps.map.Display(document.getElementById("mapContainer"), {'zoomLevel':4, 'center':[53.1, 15.1]});
 
var clicked_location = "";
var myContainer;
 
map.addListener("click", eventListener); // add the listener for mouse click
 
map.set("baseMapType", map.NORMAL);
 
function eventListener(event){
alert("in EventListener");
clicked_location = map.pixelToGeo(event.displayX, event.displayY);
alert(clicked_location.toString());
alert("Adding a Marker there");
add_Marker_where_clicked();
}
 
 
function add_Marker_where_clicked(){
myMarker = new nokia.maps.map.Marker(clicked_location);
map.objects.add(myMarker);
}
</script>
</body>
</html>

For more on the Nokia Maps API

Please check out the Nokia Maps API full documentation and API reference here:

You may also access the interactive API explorer

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