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Guest Kerry

Position Update Intervals

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Guest Kerry

Anybody have subjective data (excluding manual specs) on actual position update intervals v position output intervals for various receivers?

 

Position update interval = calculation of complete new position.

 

Position output interval = the position output rate to display etc.

 

Cheers, Kerry.

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Guest Geoffrey

Normal position updates from satellites is 1 per second, or Battery Saver Mode usually is once every 5 seconds. The satellites transmit position data once per second I believe. Most receivers Receive and Display at an interval of Once per second, but Battery saver mode changes that to less often.

 

You would have to check each GPS model for it's Battery saver mode, on how often it allows a read from the satellites, and how often it updates the display.

 

[This message has been edited by Geoffrey (edited 01 October 2001).]

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Guest Kerry

The following link is what this query is based on. The data represents ALL possible output from a common recreational handheld (fixed position) and covers a 2 minute window (Oct 1, 2001 as per date/time). The original data file is 24 hours and basically follows this extracted window pattern as well.

 

http://www.cqnet.com.au/~user/mattk/gps/gpw_2_xyg.htm

 

The as recorded data is reduced to show the precision (not practical accuracy in real terms) commonality of the positions. I've coloured the common lat/Long blocks as well as the time periods which show there was no change in something? for some quite long periods.

 

So what's that something? based on the data that shows 59 "output" positions during approx 2 minutes with only 4 unique positions (longest period without change 56 seconds)

 

Display update rate = 1 every 2 seconds (generally)

Position update = 4 times in 2 minutes (range 4 to 56 seconds)

 

- is the GPS system/atmospherics currently that stable as not to change for periods of around 60 seconds?

- does the common position blocks represent a single computation that is output many times over? (until the receiver gets around to computing another)

- does this 2 second (on average) output represent the internal updates?

- how does this type of position update affect the averaging principles?

- difficult to determine but would a moving antenna show a similar trend in position updates v output?

- is this blocky type change in position updates a function of the receivers capable output/display precision? in other words possibly wanders around in a 2-3m circle (precision limitation) before deciding the change is enough to warrant an update?

 

Geoffrey, theoretically the satellites are simply transmitting pulses at the speed of light. On average time to reach earth is 0.07 seconds which again theoretically gives a genuine unique 14 positions per second. The update rate should then be a function of the receiver's processor capability/speed and software functions. It's there if the receiver can keep up with the data flow/rate.

 

Genuine 10 update per second receivers are available (at a price of course). The aircraft carrier landing system actually runs at 20 updates/second.

 

That once per second interval quoted for most receivers gets back to the original query, based on what?

 

Cheers, Kerry.

 

[This message has been edited by Kerry (edited 01 October 2001).]

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Guest Geoffrey

s from the track log memory?? or what?? You can change the tracklog to time record and set that to 1 per second. Then leave the GPS on a rock or something, then look at the downloaded tracklog on your data transfer software. If you do that with the tracklog settings, your position screen should show updates every second. These units are only consumer units, and not professional equipment. GPS units ive had can be a bit quirky. Its like they can skip a heartbeat sometimes often.

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Guest Kerry

Geoffry, it's interesting what different units do actually and unfortuneately one can't get hold of every thing that sprouts an antenna to check it out (but I beg, borrow and steal whenever I can).

 

A 1 second update from what I've seen is very rare for normal rec/marine type receivers. The only one that I've got the data on that's done it came out of Japan.

 

I'll agree the heartbeat is difficult to see without the data. One particular make/model (top of the line model at that) I've got data for only averages an update every 5.3 seconds (range 4 to 7 seconds) which is very noticeable even on the screen.

 

It amuses me when almost every manual one picks up has the position update rate at 1 second?

 

Cheers, Kerry.

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Guest Geoffrey

I have taken the Garmin III on flights, and noticed it was working hard to display an updated position every second. On older GPS units, ive noticed even the time displayed will skip a second, like going from 12:45:12 to 12:45:14, so that is showing me how sluggish the unit is.

 

There are 3 parts to a GPS:

 

First part is a satellite receiver, which receives once per second.

 

Second part is the microprossesor and software which calculates the distance to each satellite, then triangulates a position fix for your location. Then has to covert to a format that can be displayed. Finaly the GPS saves that position fix to memory, to compare with the next position update, to comeup with things like speed over ground.It then saves that as a breadcrumb in the tracklog(If turned on).

 

Third part of the GPS is the LCD Display, and the Data output port. It has to covert the raw data in the GPS to pixels on the screen, and to the data output port(Which can be turned off to save battery too).

 

Ways to guarentee faster updates:

1) Turn off battery saver.

2) Turn off WAAS, and any other feature.

3) Turn off tracklog or Data output, but not both.(Record to tracklog or Laptop)

4) Turn off Navigation like GOTOs and Routing.

5) Also a cold GPS in the winter is sluggish.

To get Maximum battery life, turn off all these features. Amazingly I have been using my GPS alot without turning off the data output port, even when Geocaching. To save alot of battery, goto setup and select Interface(On garmins), that is in the Setup menu. Select none, and that will turn off the data output port. Also if you are tracking with GPS and laptop, turn off all features, but have the Output port turned on.

 

Extremely Technical link:

http://www.topconps.com/Technology/GPS%20Innovations.htm

Also Etremely Expensive too:

http://www.topconps.com/Sales/Product%20Price%20List.html

 

My WebPage:

http://hometown.aol.com/geoffr524/myhomepage/howto.html

 

[This message has been edited by Geoffrey (edited 04 October 2001).]

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