Electronic compass

[dispicable]

Howdy

 

This electronic compass marlarky is getting me a bit confused, for instance if I program in a cache and go to the navigation screen (coincidently the one with the compass rose)and the compass needle orientates so that it is pointing in the direction of the cache (or puts a marker on the rose, and the needle is the direction of travel) is it using the electronic compass, esp when I'm moving? Or is it registering my position in relation to the cache?

 

Cheers

[+Chrysalides]

This electronic compass marlarky is getting me a bit confused, for instance if I program in a cache and go to the navigation screen (coincidently the one with the compass rose)and the compass needle orientates so that it is pointing in the direction of the cache (or puts a marker on the rose, and the needle is the direction of travel) is it using the electronic compass, esp when I'm moving? Or is it registering my position in relation to the cache?

When you are moving with good satellite reception, the GPS receiver knows where you are a second ago, and where you are now, and can calculate your direction of travel, so it can show you an arrow pointing to where the cache is.

 

When you are standing still, the GPS receiver does not know where you are facing, unless it has an electronic compass. It will show an arrow, but where it is pointing to is its best guess of where you're facing. If you have turned around while standing in the same spot, that could be anywhere. Even if you haven't, it's still iffy (imprecisions with the GPS could mean your receiver thinks you've moved even when you're standing still).

 

Most GPS receiver with an electronic compass will use the calculated arrow when you're moving, and the electronic compass when you are not, to save power.

Edited June 2, 2011 by Chrysalides

[dispicable]

Most GPS receiver with an electronic compass will use the calculated arrow when you're moving, and the electronic compass when you are not, to save power.

 

Perfect that is exactly the answer I was looking for!! Its how I thought they should work but i always like to double check things.

 

Thanks very much!!!

[+dfx]

for instance if I program in a cache and go to the navigation screen (coincidently the one with the compass rose)and the compass needle orientates so that it is pointing in the direction of the cache (or puts a marker on the rose, and the needle is the direction of travel) is it using the electronic compass, esp when I'm moving? Or is it registering my position in relation to the cache?

 

I'm not sure if I understand the question completely, especially the last part. Because the GPS device is doing both: You are here (according to the calculated GPS position) and the cache is over there (according to the saved coordinates). From those two pieces of information, the device will know the distance from here to the cache, and in what direction it is from here. The marker on the compass rose will reflect this direction: if the cache is precisely due east from here, then the marker will be precisely on the "east" spot on the compass rose. Obviously this will change as you move, and so will the marker (and the distance shown). The electronic compass doesn't apply to any of this.

 

The other, actually unrelated question is, what part of the compass rose is shown as being "up" on the screen. While you're moving, it will simply be your direction of movement. If you're moving precisely south, then the "south" of the compass rose will be at the top of the screen. Change your direction of movement and the compass rose will rotate. The electronic compass still doesn't apply here.

 

The electronic compass only applies when you're standing still, because then, there's no direction of movement (since there's no movement) and so the only way for the device to know what part of the compass rose to move "up" is with an electronic compass. Without it, the compass rose would be stuck in its last position, but with it, it will rotate with you as you rotate on the spot, always moving the direction you're currently facing "up" on the screen. That's all it does. If you stand on the spot and look south, the "south" will move to "up" on the screen. Turn to your left and the "east" will move to the top.

 

Most GPS receiver with an electronic compass will use the calculated arrow when you're moving, and the electronic compass when you are not, to save power.

 

I don't think they do that to save power. Accuracy and intuitiveness seem much more plausible reasons to me.

[+ecanderson]

Howdy

 

This electronic compass marlarky is getting me a bit confused, for instance if I program in a cache and go to the navigation screen (coincidently the one with the compass rose)and the compass needle orientates so that it is pointing in the direction of the cache (or puts a marker on the rose, and the needle is the direction of travel) is it using the electronic compass, esp when I'm moving? Or is it registering my position in relation to the cache?

 

Cheers

Depends upon which GPS you have and how it is configured. Any Garmin (with a mag compass) for example, as at least one configuration option associated with its function that will change what is displayed under different circumstances. Some even let you set a speed below which the magnetic compass kicks in. So the generalizations are nice, but you need to tell us what model so we can first point you to the configuration options and discuss those with you so you'll know what to expect based upon how you're set up.

[John E Cache]

The mag sensor tells the GPS how the GPS aligns with the earth unconditionally. Anyone who thinks about "direction of travel" or "top of screen points here" or "speed of travel" is very old school because none of those phrases apply when the sensor is on. The compass rose aligns with the earth, the map aligns with the earth and the bearing pointer points at the destination no matter which way you travel or point the GPS. Try walking and turning the GPS any direction and everything will swing around to align with the earth.

[+fizzymagic]

The mag sensor tells the GPS how the GPS aligns with the earth unconditionally.

 

Incorrect. The mag sensor tells the GPS how the GPS aligns with the local magnetic field. That field may or may not align with "the Earth."

[John E Cache]

The mag sensor tells the GPS how the GPS aligns with the earth unconditionally.

 

Incorrect. The mag sensor tells the GPS how the GPS aligns with the local magnetic field. That field may or may not align with "the Earth."

The GPS knows how the GPS is aligned with the earth because the GPS knows the magnetic declination. I have been posting about the "compass" a lot and mainly the posts are aimed at very smart people because smart people tend to know so much they tend to over complicate things. I made a very simple statement that can be dissected in a complicated way. The mag sensor simplifies things if you don't over think it, in my opinion..

[+dfx]

Anyone who thinks about "direction of travel" or "top of screen points here" or "speed of travel" is very old school because none of those phrases apply when the sensor is on. The compass rose aligns with the earth, the map aligns with the earth and the bearing pointer points at the destination no matter which way you travel or point the GPS. Try walking and turning the GPS any direction and everything will swing around to align with the earth.

 

This ignores the fact that the GPS will stop using the builtin compass while it's moving. Try holding the GPS upside down while driving in the car. The compass rose will not rotate to align with the earth and neither will the map, it will align with your direction of travel, so it will point the wrong way. The same applies to when you're walking, if you're walking fast enough.

Edited June 4, 2011 by dfx

[+eusty]

The same applies to when you're walking, if you're walking fast enough.

My GPSr switches at 10mph...so unless I'm being chased by an animal then there is no chance of this happening!!

[+fizzymagic]

The mag sensor tells the GPS how the GPS aligns with the earth unconditionally.

Incorrect. The mag sensor tells the GPS how the GPS aligns with the local magnetic field. That field may or may not align with "the Earth."

The GPS knows how the GPS is aligned with the earth because the GPS knows the magnetic declination.

Incorrect, again. It knows the declination, so in the absence of any local deviations in the magnetic field, it knows approximately the alignment with the Earth.

 

But in practice, local magnetic fields from high-iron rocks, metal, etc. make use of the magnetic compass quite unreliable, especially in urban areas.

[+dfx]

The same applies to when you're walking, if you're walking fast enough.

My GPSr switches at 10mph...so unless I'm being chased by an animal then there is no chance of this happening!!

Well, that's yours, others are different. Mine seems to switch at approximately 5 km/h (there's no setting for it).

[jholly]

The same applies to when you're walking, if you're walking fast enough.

My GPSr switches at 10mph...so unless I'm being chased by an animal then there is no chance of this happening!!

Well, that's yours, others are different. Mine seems to switch at approximately 5 km/h (there's no setting for it).

and mine switches below 2 mph for more than 5 seconds - there is a setting for it.

[John E Cache]

OK, I will try again. If you lay a straw across the face of the GPS so it covers the N and S on the compass rose, one end of the straw points S and one end points N to incredible accuracy when compared to guessing what the GPS thinks your direction of travel is(the GPS uses inaccurate positions to guess your direction) and pointing the top of the screen that way. The S on the rose points S unconditionally. For this reason, I do not setup the GPS to turn of the sensor when moving, but that's just me. If you lay the straw on the bearing pointer and look through the straw, you can see the cache.

[John E Cache]

The mag sensor tells the GPS how the GPS aligns with the earth unconditionally.

Incorrect. The mag sensor tells the GPS how the GPS aligns with the local magnetic field. That field may or may not align with "the Earth."

The GPS knows how the GPS is aligned with the earth because the GPS knows the magnetic declination.

Incorrect, again. It knows the declination, so in the absence of any local deviations in the magnetic field, it knows approximately the alignment with the Earth.

 

But in practice, local magnetic fields from high-iron rocks, metal, etc. make use of the magnetic compass quite unreliable, especially in urban areas.

I guess I don't see your point. Or are you going to nitpick everything I say? Would you say Galileo's conclusion was wrong when he dropped two things off of the Tower of Pisa because he didn't consider air or even terminal velocity. Some statements are simplifications. That doesn't mean the idea behind the statements are wrong, in my opinion. BTW you forgot magnetic fields from motors and radio antennas.