[Loadstone] Direction change

Kerry and Gemma Hoath kerryandgemma at gotss.net
Tue Dec 2 01:36:48 GMT 2008


Gps direction is rarely accurate as it can only calculate a change in 
direction based on previous locational data.
Given that the update interval on most receivers is 1 second, and by 
definition short-term direction changes are inaccurate most software 
introduces a fudge factor which says "don't change the direction unless you 
see 3 seconds of this"

Also note that the direction is undefined when you are turning as the area 
involved is small (smaller than the accuracy of gps in many cases) and your 
direction is changing with little change to location.
Try this for an experiment:
Stand still, hold the gps receiver the right way around. now turn the 
receiver by 180 degrees. Note your direction does not change.
This shows that it is the co-ordinates received by the receiver that give it 
its idea of direction and not the orientation of the receiver. This means 
it'll give accurate readings when it is upside down in your pocket.

Now take the readings from a gps with static navigation turned off and the 
direction will bounce around from second to second, north, east, south, 
north, west, southwest and so on.

A gps needs a history of readings to calculate direction, and by default the 
update interval is 1hz. As discussed on this list, increase that and you'll 
potentially overload the phone with data it might not be able to use, and 
the processing requirements increase potentially beyond the ability of the 
phone to cope.

It also depends on the firmware of the gps as to which nmea sentences it 
sends when; there is a program with gpsd for Linux that will show you how 
often these sentences get sent. Not sure if SiRFdemo can do this also.

If loadstone doesn't get timely data from the gps, it can't use it. If it 
gets bad data, it can't use it.

It would be well to remember you are using a series of satelites in 
geostationary orbit to track your location; and not a differential source. 
If you had a ground-based differential source and the ability to use it; 
you'd be able to potentially get far more responsive direction information.

In short you are asking potentially too much of a program that runs on a 
slow hardware platform with unreliable to downright useless gps information 
from a given receiver in a potentially hostile urban environment depending 
on where you live.
You have multi-path echo, drift and interference to contend with.


Shane Rob and co feel free to correct any shortcomings in this explanation 
as i'm doing it from memory.

----- Original Message ----- 
From: "Przemysław Rogalski" <Rogalski at o2.pl>
To: <loadstone at loadstone-gps.com>
Sent: Tuesday, December 02, 2008 9:36 AM
Subject: Re: [Loadstone] Direction change


It seems that it takes about 5 seconds (I mean, when I am pressing key 1 
rapidly while I change my direction, that change will be observed after 5 
seconds). I will turn software heading - maybe it will help?
----- Wiadomość oryginalna ----- 
Od: "Stephen Giggar" <sgiggar at sbcglobal.net>
Do: <loadstone at loadstone-gps.com>
Wysłano: 1 grudnia 2008 23:52
Temat: Re: [Loadstone] Direction change


> Przemyslaw
>
> Unless you are going at very fast speed witch is not likely while walking! 
> A response of 1 second to
> detect a major change in direction is very fast response. Other product 
> take much longer to detect
> and change. Also keep in mind; If you are moving very slowly it may take 
> much longer to detect a
> change being you would have not moved very far from your initial spot. So 
> if you are asking if it
> will detect a change if you stop and move lets say back 2 or 3 feet. The 
> answer is probably no.
>
> Signed: Stephen Giggar
> Skype: dr-phone.
>
> Hardware eventually fails, software eventually works.
> No amount of bandwidth can fix poor design.
> ----- Original Message ----- 
> From: "Przemyslaw Rogalski" <Rogalski at o2.pl>
> To: "LoadStone Lista" <Loadstone at loadstone-gps.com>
> Sent: Monday, December 01, 2008 2:37 PM
> Subject: [Loadstone] Direction change
>
>
>> Hello,
>> How fast should Loadstone react to direction change? It seems that it 
>> takes more than one second.
>> Is it true?
>> I use Loadstone v0.70 on Nokia N82 and receiver G-Space GS-R238.
>> _______________________________________________
>> Loadstone mailing list
>> Loadstone at loadstone-gps.com
>> http://www.loadstone-gps.com/mailman/listinfo/loadstone
>
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