Question: What good is a compass if the iPad Wifi model doesn't have GPS?

[PinkyMacGodess]

Actually it is "true GPS" or whatever phrase you'd use. It just uses cell towers to find a general position quickly before using the satellite for the more precise location. In my experience it's much better than something like a handheld Garmin which can totally freak out and take minutes to find itself if you, say, turn it off in California then turn it back on again halfway across the country.

So the cell towers 'jump start' the location finding. Cool. And the cell towers provide the maps unless you 'pre-cache' them...

 

[vini-vidi-vici]

It's not really for determining direction

Compasses don't always point north. You have to know where someone is to know what the magnetic declination at that location is, and factor that in. I'm not sure if Star Walk does this, but I think so, as it is aware of your location via pseudo-GPS.

The compass is more useful for applications that want to know your relative change in physical direction, so if you've moved the iPad 90 degrees to your left, it'll know that. I can envision a game where via a combination of the accelerometer and compass you could move the iPad around like a window unto a virtual world... where you most likely would shoot things (since that's what games seem to be all about these days).

I would be curious to know exactly how the compass is oriented. Is it stuck to a particular plane? if so, is it parallel to the screen, or perpendicular to it? (starwalk would seem to indicate it's perpendicular to the screen) Or, is the compass "spherical" such that it's always perpendicular to the ground?

 

[markosb]

I've been using it for star apps. It's quite handy actually.

 

[PinkyMacGodess]

Compasses don't always point north. You have to know where someone is to know what the magnetic declination at that location is, and factor that in. I'm not sure if Star Walk does this, but I think so, as it is aware of your location via pseudo-GPS.

The compass is more useful for applications that want to know your relative change in physical direction, so if you've moved the iPad 90 degrees to your left, it'll know that. I can envision a game where via a combination of the accelerometer and compass you could move the iPad around like a window unto a virtual world... where you most likely would shoot things (since that's what games seem to be all about these days).

I would be curious to know exactly how the compass is oriented. Is it stuck to a particular plane? if so, is it parallel to the screen, or perpendicular to it? (starwalk would seem to indicate it's perpendicular to the screen) Or, is the compass "spherical" such that it's always perpendicular to the ground?

The magnetometer is actually called a 'Hall effect sensor' and should work at any angle...

 

[jtara]

I think we can establish from the responses here that most iPod users are not game players, LOL! Somebody FINALLY mentioned "games" as a reason for having the compass.

(For the record, I'm not a game player either, but I have worked in the industry...)

The compass allows a game to establish which direction you are facing. It should take a lot of imagination to realize that a lot of games might find this useful.

You might think that the accelerometer could be used for this using equations of motion, but you'd be wrong. The accelerometer can tell an app that you are moving left or right, or even that you are rotating left or right, but it's not accurate enough to establish just where you started and ended. So, it can't say that you rotated 20 degrees to the right.

The compass gives apps the ability to read your horizontal orientation precisely (subject, of course, to the wandering location of the magnetic north pole!).

This is useful for games that interact with the real world in some way. For example, other players in the same physical room.

 

[PinkyMacGodess]

Regarding the magnetic variation, it's true that 'true north' and 'magnetic north' aren't the same for many sites, however, only airplanes and highway construction companies (survey firms too) really should be concerned at the variation. I doubt that aside from the above people, and a few nerds and geeks, would know what the variation is at their location and which way it is in reference to 'true north'. Once the flip starts, well, we probably should pay attention but it's still unlikely to be important as with GPS, you really don't need to know the difference.

Also, a Hall effect sensor cal tell if there has been a change in direction based on the changing of the sensor output. I don't know if that is what they also use for the accelerometer, but It could be I suppose. Has anyone experimented with a strong magnet to see of the iPhone reacts well to movement?

 

[PinkyMacGodess]

The 'magnetometer' in the iPhone 3Gs (and probably the iPad) is an AKM Semiconductor 3-axis Hall Effect sensor:

• 3-axis monolithic Si-Hall Effect magnetic sensor
• Geomagnetic heading and temperature processed in sequence
• 8-bit DAC for offset compensation
• 8-bit ADC digitizes output data
• EEPROM stores calibration data
• Temperature compensated
• I2C control interface
• Integrated oscillator eliminates external CLK
• Automatic power-down mode

The output is a vector that describes direction and magnitude, which can be translated into a directional heading. The silicon magnetic sensor enables a wide measurement range and provides an excellent signal-to-noise ratio. AKM’s patented offset calibration software may be employed with the compass to calibrate offset induced by the static magnetic field generated inside the appliance. The solution offers a one degree resolution, with accuracy ranging from ±1° to ±5°, depending upon the parameters of the appliance design.

 

[PinkyMacGodess]

The accelerometer can tell an app that you are moving left or right, or even that you are rotating left or right, but it's not accurate enough to establish just where you started and ended. So, it can't say that you rotated 20 degrees to the right.

With 1 degree accuracy and operable in 3d, the magnetometer *could* be an accelerometer... It's hard to see in the pictures from the various tear downs of the iPhone...

 

[avaloncourt]

Regarding the magnetic variation, it's true that 'true north' and 'magnetic north' aren't the same for many sites, however, only airplanes and highway construction companies (survey firms too) really should be concerned at the variation. I doubt that aside from the above people, and a few nerds and geeks, would know what the variation is at their location and which way it is in reference to 'true north'.

Apparently you've never been on a boat traveling any notable distance. Variation and deviation are extremely important in marine navigation.

 

[eawmp1]

For those of us who want to know what direction in which we are going but have not a care in the world where we are or where exactly we are going.

 

[PinkyMacGodess]

Apparently you've never been on a boat traveling any notable distance. Variation and deviation are extremely important in navigation.

You are correct, however, I'd lump ships and boating in general into the same classification as pilots, only in two dimensions...

Funny that during ground school, the instructor was asked why he didn't carry a compass in case the one in the plane failed. He chuckled and said that the compass was the simplest mechanism in the whole plane and that he'd never seen one fail except for reasons like damage or putting metal too close to it. Plus he said, you can usually tell where you are and what direction you are flying in by the sun and landmarks and by using the radio and talking to ATC. He was asked a followup about being over open water... 'If you are flying over the ocean and can't see land, you have a much bigger problem than what direction you are flying in' he said with a laugh...

 

[PinkyMacGodess]

For those of us who want to know what direction in which we are going but have not a care in the world where we are or where exactly we are going.

remember: no matter where you go... there you are. - Buckaroo Bonzai