A great smartphone App

[Lyle Brotherton]

I was recently asked how you could check to see if a smartphone’s satnav is using GLONASS satellites, in addition to GPS satellites, and I have found an excellent free app, for Android smartphones, which does just this and much more.

It is called GPS Test, developed by Chartcross Limited
 
It has five screens (NB These are the default values/units which can easily be changed in the Settings menu):



Satnav Status On/Off (Erroneously called GPS status)
Reported accuracy in feet
A satnav signal (Signal to Noise Ration) bar chart, showing the designated number of each satellite – GLONASS satellites are reported as 65+ and the signal strength for each satellite
Beneath this is a chart showing SNR performance colours, yellow is fine on the histogram and green is excellent. The other screens are selectable at the bottom of this screen.

Your current speed, in MPH, and the local time are displayed on all screens.



The number of satellites in view
The number of satellites in use by the smartphone
Their relative location to you in the sky (skyview), shown on a rotating compass
The magnetic declination in your area – this describes the angle between true north and the horizontal trace of the local magnetic field and it is not the value we need to use in Great Britain when working with the British National Grid, as used on Ordnance Survey and Harveys Maps.
TTFF (Time to First Fix) how quickly your smartphone determined your location – this is when it first determined your location which could be at an accuaracy of more than 100 feet, as the unit settles your position becomes more accurate.




Your current location displayed in Latitude and Longitude using the WGS84 datum
Your current location on a world map.
The current position of the sun
Day/night transition curve (shaded areas)



Your current speed in MPH
Heading in degrees True north
Altitude in feet



Date UTC (Universal time code) this may be different to your local date
Current time read from the GPS satellites in UTC (Universal time code) – the most accurate information displayed on your satnav
Local date
Local time in your current timezone
Sunrise & sunset times at your location

Link to app
https://play.google.com/store/apps/details?id=com.chartcross.gpstest&hl=en

[ianj37]

Thanks for sharing Lyle, that's an impressive piece of software, even more so as it's free, and interesting because I keep looking at this:

http://tgomagazine.co.uk/gearreview/first-look-quechua-mountainproof-quechuaphone-5-0

and wondering whether it's for me - but I am still trying to love my new GPSMap 62s (difficult though it may be on occasions)!

Ian

[captain paranoia]

GPS Status is a similar app, and is how I figured that my Hudl has a GPS/GLONASS receiver.

I've also got GPS Test on my Hudl, but I'm afraid I was too slack to add it to the Apps page... now done

[captain paranoia]

ps. if you get a C/No figure of 99dB, you're probably next to a jammer...

Oh, and you can tell GPS Test to display in sensible units, like metres and OSGB...

[Pete McK]

Downloaded it last night and considering it is free, and free of adverts, it is quite a remarkable little app.

In the settings menu I have changed the:
* Grid reference to OSGB (Grid ref) to display the two grid letters then the easting and northing - instead of the all-numeric grid references OSGB (E,N)
* My known altitude was out by 17m To correct this I checked the Adjust altitude box, which applies the stored Geoid value and the altitude now reads within 4m of my known height.
* Altitude units to metric, measured in metres
* North reference to Magnetic

Couple of questions I would be interested to find out more about.
Anyone know how is the reported accuracy calculated, I have not as yet sat my phone next to my Etrex H to compare these values.
Why my Skyview appears exactly 180 degrees out? I have tried setting the Compass only and GPS only settings independently with no success.

[captain paranoia]

> and the altitude now reads within 4m of my known height.

Keep an eye on that error.  GNSS altitude is more variable than horizontal position, due to the constellation geometry.  You may find that your 'correction' actually makes things worse, in the long term...

How the estimated error is calculated is down to the receiver, I think.  I shall ask our GNSS Guru about how error estimates might be determined by a GNSS receiver, but the answer will involve some very complicated statistical mathematics, I'm sure...

[Lyle Brotherton]

Nice configuration Pete

The most common user error with the digital compasses that most smartphones incorporate is that they are 2-axis and not 3-axis, therefore they need to be held horizontally to function correctly.

Let me know how you get on and which smartphone you are using.

[Pete McK]

Thank you CP & Lyle Both recommendations now adopted.

My phone is an iPhone 5 and yes the compass now works accurately when held horizontally. I know from the sales blurb it came packed with that it has a digital compass, what exactly is a digital compass?

[Lyle Brotherton]

My pleasure Pete.

I did quite a bit if investigation into how digital compasses work when researching the UNM, sadly Harper Collins in their infinite wisdom  decided not to include it.

They are based on a technology called  Magneto-Inductive-Sensors

Basically they are a minute coil of wire around a ferromagnetic rod that changes permeability within the Earth's field - permeability is the degree of magnetization that the ferromagnetic core obtains in response to an applied magnetic field, which in this instance the Earth’s magnetic field.

In addition to their relative simplicity and minute size, they have other features which make them ideal for Smartphone:

-   Their output is digital, most other competing technologies provide an analogue output which require additional hardware
-   Highly sensitive, again, other technologies need additional hardware
-   Very low power consumption

Combine this with an Accelerometer, that tracks the movement of the phone (roll & pitch) and you have a very powerful piece of kit. Your iPhone has both of these, which allows it to work out the precise orientation of the iPhone as you move it about.

In the GPS Test App, the data from the Digital Compass and Accelerometer is combined with the iPhone's integrated satnav technology to provide your Grid Ref etc.

My Samsung Galaxy S3 used the same technology, as does the S4.

[captain paranoia]

A smartphone will be using a MEMS magnetometer, which is likely to use a different approach (probably Lorenz Force, or Magnetoresisitve, depending on supplier) to the one Lyle describes.

http://en.wikipedia.org/wiki/MEMS_magnetic_field_sensor
http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=06519300
http://www.memsic.com/userfiles/files/publications/Articles/Electronic_Products_Feb_%202012_Magnetometer.pdf

Functions of 3D accelerometer, 3D gyroscope and 3D magnetometer are often combined in a single silicon device, often called a 9-axis or 9 degrees-of-freedom sensor.  You will sometimes find temperature and pressure added to the sensing functions in the same device...

http://www.siliconsemiconductor.net/article/79083-ST-targets-sophisticated-electronics-with-9-axis-MEMS-sensor.php
http://cache.freescale.com/files/sensors/doc/reports_presentations/ARTICLE_REPRINT.pdf?&Parent_nodeId=129288320677672732B37A&Parent_pageType=taxonomy

For other types of magnetometer, see the Wiki article:

http://en.wikipedia.org/wiki/Magnetometer

[captain paranoia]

Oh, and these 9-axis MEMS devices are the basis of the cheap automatic pilots for microdrones (e.g. ArduPilot or ArduIMU), and are usually called an Inertial Measurement Unit, or IMU.

There's a lot of work going on to fuse IMU and GNSS data to allow the IMU to fill in when GNSS is lost, and to get the GNSS to measure and correct for the drift of the IMU; drift is the big problem with these cheap IMUs.

[boogyman]

Nice app ! Does anyone know "when" (as in: for which screen, for which data) the app goes on-line?

[Lyle Brotherton]

Chris if I have understood your question correctly, the app is available now.

PS Did you also receive my email 27042014?

[Lost Soul]

What great app.  Have installed it on my Samsung Note 8 Tablet.  At least it has answered to question does it use Glonass as well as GPS?  Yes it does.

[Callum]

Fantastic app Looked at the upgrade, which gives you navigation and might try it - there is a try it first before you buy. I thought the HUD for your car was novel, where your smartphone projects your current speed onto the windscreen of you car, pointless, but fun