Advanced Geolocationfor the Mobile Web

Andy Gup, @agup

How to get a good location

Challenges

Solutions

Smartphone/Tablet GPS

Built for consumer use-cases

Accuracy only needs to be “good enough”

Tiny antenna on bottom of device

Geolocation Object

Say what, 4887 meters accuracy???

Indoors using WiFi-only

Demo

http://github.com/esri/html5-geolocation-tool-js

Best possible accuracy…under perfect conditions

3 – 10 meters

10 – 33 feet

Problem 1: location fluctuations

Problem 2: all locations lumped together

Network location

GPS location

??

Use case: Stationary…

5 minutes!

Problem 3: Accuracy will vary

Bad

So-so

GoodTime vs Accuracy

Problem 3: Accuracy will vary

Bad

So-so

GoodTime vs Accuracy

Accuracy vs Precision

Low AccuracyHigh Precision

High AccuracyLow Precision

High AccuracyHigh Precision

Problem 4: GPS needs to warm up!

Initial readings less accurate or non-existent

Technical Use Case: Cold Start

GPS takes time to calibrate

Phone rebooted

Updated phone OS

Potential for no cached values

Potential for large inaccuracy

Technical Use Case: Warm start

GPS has been in use continuouslyGPS is (mostly) calibrated

Highest potential for accuracy and precision

Using the Geolocation API options

errorHandler()

Timeout

maximumAge – used only during startup

enableHighAccuracy

Snapshot location – Not Reliable!

navigator.geolocation.getCurrentPosition();

watchId = navigator.geolocation.watchPosition(

processGeolocation,

/* OPTIONAL */

geolocationError,

{

timeout: 0,

maximumAge: Infinity,

enableHighAccuracy: true

}

);

Continuous location

maximumAge (ms)

Max age of cached position in milliseconds

“0” – do not use cache

“Infinity” – (default) return any cached value

timeout (ms)

Max milliseconds to return a positionThrow error if no location at timeoutWith watchPosition() can throw error repeatedly

“Infinity” – (default) don’t return until position available

enableHighAccuracy(boolean)

Try to obtain best possible result

If GPS available and perms enabled -- use it

If Geolocation Service available -- use it

– Requires an internet connection!

– WiFi and/or Cellular

watchPosition scenario 1:

{

timeout: 30000,

maximumAge: 300000

}

Request result < 30 secondsAccept cache value < 5 mins old

watchPosition scenario 2:

{

timeout: 60000,

maximumAge: Infinity

}

Request result < 1 minuteReturn any cache value

watchPosition scenario 3:

{

timeout: 60000,

maximumAge: 0,

enableHighAccuracy: true

}

Request result < 1 minuteDo NOT use cache, try GPS

Browser Geolocation AccuracyDepends on …

Type of browserType of deviceWi-Fi On/OffGPS On/OffLocation user permissionsVPN

Force phone to use GPS

Solution 1: Post-process bufferingSolution 2: Cordova pluginSolution 3: 1 and/or 2 + external GPS

Solution 1:Buffering to determine center point

Capture many points

Average all values

Calculate centroid

[{lat:-120,lon:35}, {lat:-120.01,lon:35.1}, {lat:-120.011,lon:35.02}, {lat:-120,lon:35.1}, {lat:-120,lon:35}]

JavaScriptData Collection

Field location template

github.com/esri/html5-geolocation-tool-js

Solution 2:Cordova/PhoneGap & Geolocation

Taps native SDKs via plugins

Direct access to geolocation functionality

Can track geolocation while in background

Battery usage optimization

cordova-plugin-advanced-gelocation

https://github.com/Esri/cordova-plugin-advanced-geolocation

Separates GPS from Network location

Multi-threaded for high performance

Calculates centroid

Android only!

Native functionality

Separates network locations

from GPS locations

External GPS

Can provide greater accuracy and precision

Can provide faster location acquisition

Connect via USB or Bluetooth

Example: Trimble R1Sub-meter accuracy*

Works with Geolocation API

Overrides onboard GPS

Works on iOS and Android

On extra step on Android

A GPS Experiment

START POINT

Commercial GPS Smartphone GPS

Solution 3: buffer, plugin + external GPS

Take a close look at use casesStudy your requirements

Recap

Consumer vs Commercial case casesConsumer vs Commercial equipment

Accuracy vs Precision

Getting the best static location

Questions?

Andy Gup, Esri Developer Advocatehttp://www.andygup.netagup@esri.com@agup

Works with..

Works with…