Geolocation and Mapping

Geolocation
&
Mapping
Ivano Malavolta
ivano.malavolta@univaq.it
http://www.di.univaq.it/malavolta

Roadmap
• Introduction
• Geolocation
• Google Maps Services*

* In this lecture we refer to Google Maps Services only because of space
limitations. Other services, like Yahoo! Place Finder, can be used as valid
alternatives

Geolocation

Geolocation is the identification of the real-world
geographic location of an object, like

• mobile phone
• Internet-connected computer terminal

Geolocation may refer to the practice of assessing the
location, or to the actual assessed location

Mapping

Mapping usually refers to map-making and often
used instead of cartography

Geolocation VS Mapping
Geolocation refers to geospatial
data collection and manipulation

ex. LatLon calculations, geocoding, etc.

Mapping refers to the activity of
creating a map through some
cartographic works

ex. maps, layers, markers, routes, etc.

Roadmap
• Introduction
• Geolocation
• Google Maps Services*

* In this lecture we refer to Google Maps Services only because of their high
understandability and stability. Other services, like Yahoo! Place Finder, can
be used as valid alternatives

Geolocation
navigator.geolocation

Provides access for capturing location information for
the device, like:

• latitude
• longitude
• Speed

Geolocation

The API itself is agnostic of the underlying location
information sources

Common sources of location information include
• Global Positioning System (GPS)
• location info from IP address, RFID, WiFi,GSM
cell IDs, etc.

No guarantee is given that the API returns the device's
actual location

Geolocation Methods
The geolocation object provides 3 methods:

• geolocation.getCurrentPosition
• geolocation.watchPosition
• geolocation.clearWatch

getCurrentPosition

It returns the device's current position

getCurrentPosition(win, [fail], [options]);

win
callback function with a Position parameter
fail
error callback
options
geolocation options

watchPosition
It gets the device's position when a change in position has
been detected

var id = watchPosition(win, [fail], [options]);

win
callback function with a Position parameter
fail
error callback
options
geolocation options

clearWatch

Stop watching the Geolocation referenced by the
watch ID parameter

clearWatch(watchID);

watchID
ID returned by geolocation.watchPosition

Options

• frequency (Number)
– How often to retrieve the position in milliseconds
• enableHighAccuracy (Boolean)
– Receive the best possible results
• timeout (Number)
– The maximum length of time (msec) that is allowed to pass
from the call until the corresponding callback is invoked
• maximumAge (Number)
– Accept a cached position whose age is no greater than the
specified time in milliseconds

The Position object

Contains the data created by the geolocation API

It is passed as argument to the success callbacks of
getCurrentPosition and watchPosition

Properties:
coords:
coords: A set of geographic Coordinates seconds in iOS
timestamp: Creation timestamp in milliseconds

The Coordinates object

A set of properties that describe the geographic
coordinates of a position

The Coordinates object is created and populated by
Cordova, and attached to the Position object


Properties:

• latitude (Number)
– Latitude in decimal degrees
• longitude (Number)
– Longitude in decimal degrees
• accuracy (Number)
– Accuracy level of the latitude and longitude coordinates in
meters

http://bit.ly/Ln6AtM

null in Android

• altitude (Number)
– Height of the position in meters above the ellipsoid
• altitudeAccuracy (Number)
– Accuracy level of the altitude coordinate in meters

http://bit.ly/Ln7V3H


• heading* (Number)
– Direction of travel, specified in degrees counting
clockwise relative to the true north
• speed (Number)
– Current ground speed of the device, specified in meters
per second
The Compass API in Cordova is
exclusively dedicated to the
heading property

http://bit.ly/LnanXV

Position Error

Encapsulates the error code resulting from a failed
position capture operation

It contains a pre-defined error code
pre-

PositionError.PERMISSION_DENIED
PositionError.POSITION_UNAVAILABLE
PositionError.TIMEOUT

Example
var options = { maximumAge: 3000, timeout: 5000,
enableHighAccuracy: true };

navigator.geolocation.watchPosition(win, fail, options);

function win(pos) {
var el = ‘<div>Latitude: ‘ + pos.coords.latitude + '</div>');
el += ‘<div>Longitude: ‘ + pos.coords.longitude + '</div>');
el += ‘<div>timestamp: ‘ + pos.timestamp + '</div>');
$(‘#block’).html(el);
}

function fail(err) {
console.log(err.code);
}

Google Maps API

The Google Maps Javascript API lets you embed Google
Maps in your app

The latest version (v3) of this API
is especially designed to be faster
and more applicable to mobile
devices

http://www.cibando.com

Goole Maps API

The API provides a number of utilities for manipulating
maps and adding content to the map through a
variety of services

You can see it like a way to programmatically manage
maps on http://maps.google.com

GMaps Basics
google.maps.Map

This object represents a GMaps map

it will contain the maps along with all the other
elements, like markers, polygons, etc.

GMaps Basics
Here is its constructor:

google.maps.Map(htmlElement, options);

• htmlElement
– a reference to a HTML element where you want the
map to be inserted
• for example <div id=“map”></div>
• options
– an object literal containing a set of properties

GMaps Basics

The options parameter may have these properties:

• center (google.maps.LatLng)
– the center of the map
• zoom (Number)
– the initial zoom-level of the map
• mapTypeId (google.maps.MapTypeId)
– what kind of map type that would initially be used
– The most common type is google.maps.MapTypeId.ROADMAP

GMaps Basics

• draggable (boolean)
– if false, prevents the map from being dragged
• minZoom (Number)
– the minimum zoom level which will be displayed on the map
• maxZoom (Number)
– the maximum zoom level which will be displayed on the map
• zoomControl (boolean)
– if false, hides the control to zoom in the map
• etc...

The LatLng object
It is a point in geographical coordinates:
• latitude
• longitude

ex. new google.maps.LatLng(57.8, 14.0);

The LatLngBounds object
It represents a rectangle in geographical coordinates
• south-west
• north-east

ex. new google.maps.LatLngBounds(
new google.maps.LatLng(57.8, 14.0),
new google.maps.LatLng(57.8, 14.0)
);

contains(pt), intersect(bounds), getCenter(),
union(bounds), etc.

Map Types

You must specifically set an initial map type at this
time as well

mapTypeId: google.maps.MapTypeId.ROADMAP

Supported types:
• ROADMAP
• SATELLITE
• HYBRID
• TERRAIN

Example
// in your JS file
var options = {
center: new google.maps.LatLng(-34.397, 150.644),
zoom: 8,
mapTypeId: google.maps.MapTypeId.ROADMAP
};
var map = new
google.maps.Map(document.getElementById(“map”),
options);

// somewhere in your HTML templates
<div id=“map”></div>

GMaps Events

There are 2 types of events:

• User events
– are propagated from the DOM to the Google Maps API
– for example click

• MVC state change notifications
– reflect changes in Maps API objects and are named using
a property_changed convention
– for example the API will fire a zoom_changed event on a
map when the map's zoom level changes

Map Event Listeners
You register for event notifications using the
addListener() event handler

google.maps.event.addListener(obj, eventname, callback)

• obj the object on which the event can occur
obj:
– ex. the whole map, a marker, etc.
• eventname an event to listen for
eventname:
– ex. “click”, “center_changed”, “zoom_changed”, etc.
– every objects can respond to different types of events
• callback function to call when the specified event
callback:
occurs

DOM Object Events

It allows you to capture events occurred on elements
within the DOM

addDOMListener(obj, eventname, callback)

It is similar to addListener, but here obj can be any
element within the DOM

Example
var map = new
google.maps.Map(document.getElementById(“map”),
opt);

google.maps.event.addListener(map, 'click',
function(event) {
var marker = new google.maps.Marker({
position: event.latLng,
map: map
});
map.setCenter(marker.getPosition());
}
);

GMaps Overlays

Overlays are objects that you “add” on the map like
map,
• points,
• lines,
• areas,
• collection of other objects

They are tied to latitude/longitude coordinates
so they move when you drag or zoom the map
http://bit.ly/Lztdac

http://bit.ly/LztJoV

Types of Overlays in GMaps

• Marker
– represent single locations on the map
– can be represented also by an icon

• Polyline
– an ordered sequence of locations
– represent lines on the map

In this lecture we will focus on
markers & polylines only


• Polygon
– an ordered sequence of locations
– define a region on the map

• Map Types
– represent map layers
– can replace base map tiles
– can be displayed on top of
base map tiles

http://bit.ly/LztFoV
http://www.mapofthedead.com/


• Info Window
– displays content within a popup
balloon on top of a map
– linked to a specific location

• Custom Overlay
– any DOM element that be
positioned on the map

http://bit.ly/LztFoV

Markers

Markers identify locations on the map
Markers are designed to be interactive
you can attach event listeners to them

ex.
marker = new google.maps.Marker({
// options
});
google.maps.event.addListener(marker, 'click', callback);

Marker Options
The google.maps.Marker constructor takes a single
object literal specifying the initial properties of the
marker

• position
– LatLng identifying the initial location of the marker
• map
– the Map object on which to place the marker
– You can add the marker later by calling setMap() method
– You can remove a marker by calling setMap() with null

Marker Options
• animation
– google.maps.Animation.DROP
– google.maps.Animation.BOUNCE

You may initiate an animation on an existing marker by
calling setAnimation() on the marker object
• draggable
– makes the marker draggable on the map
• icon
– used to set a custom icon for the marker
– it defines the URL of an image to be used as icon
– The Google Maps API will size the icon automatically

Polylines
A Polyline object consists of an array of LatLngs

It creates a series of line segments that connect those
locations in an ordered sequence

Similarly to Marker, the constructor of Polyline
takes an object literal containing the options

Also Polyline can react to user events

Polylines Options

• path[]
– array of LatLng, one for each point of the polyline
• strokeColor
– color of the lines in CSS syntax
• strokeOpacity
– opacity of the lines as a decimal number between 0 and 1
• strokeWeight
– the weight of the line's stroke in pixels
• editable
– boolean, specifies whether users can modify it or not

Example
var map; // the map object, initialization omitted here

var coords = [
new google.maps.LatLng(37.772323, -122.214897),
new google.maps.LatLng(21.291982, -157.821856),
new google.maps.LatLng(-18.142599, 178.431),
new google.maps.LatLng(-27.46758, 153.027892)
];

var polyline = new google.maps.Polyline({
path: coords,
strokeColor: "#00FF00",
strokeOpacity: 1.0,
strokeWeight: 1
});
flightPath.setMap(map);

GMaps Services

3 are the main services provided by GMaps:

• Directions
• Distance Matrix
• Geocoding

Directions
You can calculate directions (using a variety of methods of
transportation) by using the object

google.maps.DirectionsService

This object communicates with Google Maps which receives
direction requests and returns computed results

You can
1. manage these directions results directly
2. use the DirectionsRenderer object to render them

Direction Requests
1. create an object of type DirectionsService
2. create a DirectionsRequest object literal containing
the input terms
3. call DirectionsService.route() to initiate a
request to the Directions service
4. manage the results via a callback function manageRoute

var dirService = new google.maps.DirectionsService();
var request = {
origin: ”…”,
destination: “…”,
travelMode: google.maps.TravelMode.DRIVING
};
dirService.route(request, manageRoute);

Directions Results

When sending a directions request to the DirectionsService,
you receive a response consisting of

1. a DirectionsResult object
– contains an array of DirectionsRoute object, each of
them representing a route from the origin to destination
2. a status code
– OK, NOT_FOUND, ZERO_RESULTS, INVALID_REQUEST, etc.

Example of Route
destination

waypoints

origin

steps

legs

http://goo.gl/maps/ZK4H

Routes
It is an object literal with the following fields:

• legs array of DirectionsLeg objects
legs[]:
• waypoint_order indicates the order of waypoints
waypoint_order[]:
• overview_path[]: array of LatLngs approximating the
overview_path
path of the resulting directions
• bounds LatLngBounds containing the route
bounds:
• copyrights: text
copyrights
• warnings text
warnings:

Legs

• steps[]:
steps array of DirectionsStep objects
• distance:
distance total distance covered by this leg
• duration:
duration total duration of the leg
• start_location:
start_location the origin of the leg as LatLng
• end_location:
end_location the destination of the leg as LatLng
• start_address:
start_address the origin of the leg as text
• end_address: the destination of the leg as text
end_address

Steps

• instructions:
instructions instructions for this step within as text
• distance:
distance total distance covered by this step
• duration:
duration total duration of the step
• start_location:
start_location the origin of the leg as LatLng
• end_location:
end_location the destination of the leg as LatLng

Example

http://bit.ly/KtJrUM

Distance Matrix

It is a service to compute
1. travel distance
2. journey duration

between multiple origins and destinations

This service does not return detailed route information
you need the Directions Service for these

Distance Requests
google.maps.DistanceMatrixService
.getDistanceMatrix(options, callback)

where
• options
– object literals containing origin, destination, travel modes, ...
• callback
– the function executed upon response

Distance Request Options
• origins
– array containing one or more address strings and/or LatLng
• destinations
– array containing one or more address strings and/or LatLng
• travelMode
– google.maps.TravelMode.DRIVING
– google.maps.TravelMode.WALKING
– google.maps.TravelMode.BICYCLING
• unitSystem
– google.maps.UnitSystem.METRIC
– google.maps.UnitSystem.IMPERIAL
• avoidHighways (boolean)
• avoidTolls (boolean)

Distance Responses

A successful call to the Distance Matrix service
returns:

• a DistanceMatrixResponse object
• a DistanceMatrixStatus object

These are passed to the callback function you specified
in the request

DistanceMatrixResponse
It is an object containing the following properties:

• originAddresses
– array containing the locations passed in the origins field
• destinationAddresses
– array containing the locations passed in the destinations field
• rows
– array of DistanceMatrixResponseRow objects, with each row
corresponding to an origin
• elements
– are children of rows, and correspond to a pairing of the row's
origin with each destination
– They contain status, distance, and duration information for each
origin/destination pair

Example
var origin = “L’Aquila, Italy";
var destination = “London, England";

var service = new google.maps.DistanceMatrixService();
service.getDistanceMatrix({
origins: [origin],
destinations: [destination],
travelMode: google.maps.TravelMode.DRIVING,
avoidHighways: false,
avoidTolls: false
}, callback);

function callback(response, status) {
if (status == google.maps.DistanceMatrixStatus.OK) {
var t = response.rows[0].elements[0].distance.text;
alert(t);
}
}

Geocoding

It is the process of converting addresses into
geographical coordinates

ex.
“via Vetoio 1, L’Aquila” 42.362319,13.368514

A geocoder may return more than a result

You can also perform the inverse conversion
reverse geocoding

Geocoding Requests
var geocoder = google.maps.Geocoder();
geocoder.geocode(options, callback);

where
• options (object literal)
– address (String) geocoding
– latLng (LatLng) reverse geocoding
– bounds (LatLngBounds)
– region (String)
• see http://www.iana.org/assignments/language-subtag-registry
• callback
– the function executed upon response

Geocoding Responses
They are passed to the callback function as a
GeocoderResults object

Example
geocoder = new google.maps.Geocoder();
var address = “via Vetoio 1, L’Aquila”;
geocoder.geocode( { 'address': address}, callback);

function callback(results, status) {
if (status == google.maps.GeocoderStatus.OK) {
for(result in results) {
console.log(result.geometry.location);
}
} else {
console.log(status);
}
}

What’s more?
• Controls
– UI elements to allow user interaction with the map
– zoom, Street View, scale, map type
• Layers
– GeoRSS, KML, Fusion Tables, etc.
• Map Types & Styles (see http://bit.ly/JEA6Nu)
– custom styles, image overlays, etc.
• StreetView Services
• Drawing Library
– drawing tools, geometry, etc.

References

https://developers.google.com/maps/documentation/javascript/

Geolocation and Mapping

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