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North pointer

 
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victorf



Joined: 01 Jan 2006
Posts: 342
Location: Schenectady, New York
Posted: 28 April 2009, 14:14 PM    Post subject: North pointer Reply with quote
I would like to have a device that points to true north but does not rely on a magnetic compass nor upon stars. This does not seem to be feasible but I was hoping someone might have the turn of mind to propose something that might be feasible. Any ideas?

Any enlightenment will be appreciated.

Vic
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Don_Kirby



Joined: 15 Oct 2006
Posts: 329
Location: Long Island, New York
Posted: 28 April 2009, 20:33 PM    Post subject: Reply with quote
Two things come to mind. If you're moving, GPS will give you direction of travel. If you are stationary, a gyroscope will point in the same direction all the time, but you'll have to compensate for Earths' rotation.

-Don
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 29 April 2009, 3:33 AM    Post subject: Reply with quote
Don_Kirby wrote:
Two things come to mind. If you're moving, GPS will give you direction of travel. If you are stationary, a gyroscope will point in the same direction all the time, but you'll have to compensate for Earths' rotation.

-Don


You can see the orbiting ISS with the naked eye without cloudy skies. If you note its rise and set, and compare to its orbital parameters on the NASA website, you can determine your angle on the earth.

With an immobile GPS receiver, while you log the movements of the satellites, I think you can do the same as with ISS.
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cerickson



Joined: 20 May 2008
Posts: 30
Location: Waikoloa Village, HI, USA
Posted: 29 April 2009, 3:51 AM    Post subject: Reply with quote
Combining a GPS, a digital compass and some math will give you true North from magnetic North and Lat/Lon.
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spamiam



Joined: 13 Nov 2005
Posts: 666
Posted: 29 April 2009, 15:05 PM    Post subject: Re: North pointer Reply with quote
victorf wrote:
I would like to have a device that points to true north but does not rely on a magnetic compass nor upon stars.


Well, there are only 2 general techniques. Internal and external references.

Internal would be some sort of intertial system such as a gyro.

External could be magnetic, optical, and radio. You have eliminated megnetic and optical, so that leaves radio. You can take a fix by triangulation from surface radio sources, or satellite sources.

Once you get that position fix, then if you can tell what direction that any particular source is coming from relative to your heading, then you can tell the absolute direction even without moving. But I would expect it to be have rather poor accuracy until you start to move. While moving, you can get a reasonably precise measurement of your absolute heading.

Using a compass is a little easier....

-Tony
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Don_Kirby



Joined: 15 Oct 2006
Posts: 329
Location: Long Island, New York
Posted: 30 April 2009, 0:05 AM    Post subject: Re: North pointer Reply with quote
spamiam wrote:
You can take a fix by triangulation from surface radio sources, or satellite sources.


Triangulation isn't required for determining direction. A single transmitter and a directional receiver will allow for direction finding just fine. The trick is getting the transmitter to the true north pole, and making a receiver good enough to pick up the signal without line of sight, and from across the planet...

If the application is stationary however (or even confined to a small enough area), acceptable results may be obtained by using a transmitter located only a short distance away.

-Don
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spamiam



Joined: 13 Nov 2005
Posts: 666
Posted: 30 April 2009, 0:43 AM    Post subject: Re: North pointer Reply with quote
Don_Kirby wrote:
spamiam wrote:
You can take a fix by triangulation from surface radio sources, or satellite sources.


Triangulation isn't required for determining direction. A single transmitter and a directional receiver will allow for direction finding just fine. The trick is getting the transmitter to the true north pole, and making a receiver good enough to pick up the signal without line of sight, and from across the planet...


True enough! Wink But I am assuming that there is no transmitter at the pole and/or I don't have a good enough receiver.

But I may be able to read nearby transmitters which have known locations. If I have 2 of them, then I ought to be able to determine my location in relation to them, and then I can probably determine my orientation as well.

-Tony
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 30 April 2009, 6:25 AM    Post subject: Re: North pointer Reply with quote
spamiam wrote:
Don_Kirby wrote:
spamiam wrote:
You can take a fix by triangulation from surface radio sources, or satellite sources.


Triangulation isn't required for determining direction. A single transmitter and a directional receiver will allow for direction finding just fine. The trick is getting the transmitter to the true north pole, and making a receiver good enough to pick up the signal without line of sight, and from across the planet...


True enough! Wink But I am assuming that there is no transmitter at the pole and/or I don't have a good enough receiver.

But I may be able to read nearby transmitters which have known locations. If I have 2 of them, then I ought to be able to determine my location in relation to them, and then I can probably determine my orientation as well.

-Tony


on that last paragraph, I don't know how you can do that with modest equipment. Signal strength is not accurate enough. Time of arrival can be done for signals like digital TV where you know the transmitters' locations. I've seen one startup with this patent.
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twesthoff



Joined: 17 Mar 2006
Posts: 191
Location: Fredericksburg, VA
Posted: 30 April 2009, 11:28 AM    Post subject: Re: North Pointer Reply with quote
Vic,
Does this have to work anywhere on earth, or just in a region or small area?
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victorf



Joined: 01 Jan 2006
Posts: 342
Location: Schenectady, New York
Posted: 30 April 2009, 12:11 PM    Post subject: Reply with quote
Quote:
Does this have to work anywhere on earth, or just in a region or small area?


It would be nice if it could work anywhere. However, it is becoming quite clear from the posts, that such a device (as I envision it) is, at best, impractical and at worst, impossible.

I appreciate everyone's ideas and taking the time to post their suggestions. I suspect it is time to stop flogging this dead horse.

Vic
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spamiam



Joined: 13 Nov 2005
Posts: 666
Posted: 30 April 2009, 12:26 PM    Post subject: Re: North pointer Reply with quote
stevech wrote:
on that last paragraph, I don't know how you can do that with modest equipment. Signal strength is not accurate enough. Time of arrival can be done for signals like digital TV where you know the transmitters' locations. I've seen one startup with this patent.


Well, I was simply imagining some sort of direction finder. Maybe something as crude as using a directional antenna and find the strongest signal. But if using signal strength is not good enough, then this idea is scrapped.

I guess that leaves something like LORAN which apparently uses time of flight measurements.

-Tony
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twesthoff



Joined: 17 Mar 2006
Posts: 191
Location: Fredericksburg, VA
Posted: 30 April 2009, 12:45 PM    Post subject: Re: North Pointer Reply with quote
Vic,
You haven't said how accurate it has to be...

The easiest way I can think to do it would be to have GPS to know your location, a digital compass to know magnetic north, and a lookup table to correct to true north. The lookup table could be in a SD card connected to the processor. The lookup table would be time consuming to make and much easier if you didn't have to be very accurate.

Check this out:
http://geomag.nrcan.gc.ca/apps/mdcal-eng.php

Tom W
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dlh



Joined: 15 Dec 2006
Posts: 266
Location: ~Cincinnati
Posted: 30 April 2009, 12:58 PM    Post subject: Reply with quote
victorf wrote:
... it is becoming quite clear from the posts, that such a device (as I envision it) is, at best, impractical and at worst, impossible.
Without your limitation that it cannot rely on a magnetic compass (which I assume extends to magnetic sensors), it is indeed possible. See...Whether it is practical and affordable for your application is another matter.
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pjc30943



Joined: 02 Dec 2005
Posts: 220
Posted: 02 May 2009, 0:18 AM    Post subject: Reply with quote
How much can you afford? Are you outside?

Differential GPS by itself can do that with nothing else required. New chipsets can receive inside some structures fairly well--but not too deep down.
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dlh



Joined: 15 Dec 2006
Posts: 266
Location: ~Cincinnati
Posted: 30 May 2009, 10:28 AM    Post subject: Re: North pointer Reply with quote
victorf wrote:
I would like to have a device that points to true north but does not rely on a magnetic compass nor upon stars. This does not seem to be feasible but I was hoping someone might have the turn of mind to propose something that might be feasible. Any ideas?

Any enlightenment will be appreciated.

Vic

The June issue of Circuit Cellar magazine has an article (Jeff Bachiochi, p60) on Anisotropic Magnetoresistance Sensors which uses a $20 Honeywell HMC5843. You never said whether magnetic sensors were OK or not so this may not help.
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