HOLUX GR231 seems to "go wild"?

wisniak · Occasional Visitor Joined: Dec 17, 2005 Posts: 6

Hi,

I have a Holux GR-231 GPS and I use it with Destinator PN.

Lately, while navigating, the green curson denoting the car's position "goes wild" relative to the true position on the road - the cursor starts to crawl to the right or to the left, and moves to a distance of up to a few hudred meters from the road.

This happens while driving or when the car is standing still, say at a traffic light.

Other times, the cursor shows a position parallel to the road, and this can go on for several Km. O the program begins to calculate odd routes that try to get me back on track (even though I'm driving on the correct road).

This could be a sign of low satellite reception. but almost every time I checked - I had at least 7 satellites with good reception.

Could it be that the GPS has developed some fault? Is there any way to check this?

I have a Dell Axim X50 520MHZ Pocket PC.

Every time, before I begin navigation I close all programs and do a soft reset, to verify I have the maximum memory available. It doesn't seem to help.

Do you have any ideas?

Thank you,

Daniel

Bassrock · Occasional Visitor Joined: Sep 25, 2005 Posts: 24

Mmmmmmmmm

Hello,

My Guess is that there is absolutely nothing wrong with the GPS.

There is certain routes I drive, mostly when there are high tree's left and right on the stretches of road concerned, weather, or if there are high buildings, in some cases 3 to 4 stories high thats all it takes for the signal to drift. Ok doesn't happen very often, but when it does these are the pertinent offending issues/items trees and high buildings.

Be very carefull when you say I have 8 satellites with good reception "what do you mean by good reception??", my system can at times see 1 to 16 satellites, but signal strength is not strong enough to get a 2d lock never mind a 3d lock, so dependant on where you are your GPS may "see" 8 satellites but it may be struggling even to obtain a 2D fix, hence your track point moving all over the place.

You may find an external aerial, or moving the aerial in the car may help.

But again, it is my belief your GPS is ok.

Regards

Bassrock :D
_________________
Tools: Nokia 6600, Globalsat BT 318 GPS, TTM5, +1 Wife, 2 Children, mortgage etc..

wisniak · Occasional Visitor Joined: Dec 17, 2005 Posts: 6

When I encounter this erratic behavior, I usually check the satellite signal status in Destinator by pressing the satellite icon, where I can see how many satellites are locked (the satellite number is displayed), as well as signal strength (according to the length of the green bar associated with each GPS).

Another option is VisualGPS, where I can check the Sig/Nav screen. Today, for example, I checked the status in this app, and most of the time I had 7-9 satellites, and the bar associated with them displayed a value of 40+ (I don't know the meaning of this value). Most of the bars were blue, although some of them were grey (some of the grey bars had high values, some of them low, same as the blue bars).

Bassrock · Occasional Visitor Joined: Sep 25, 2005 Posts: 24

Mmmmmmm

Hello,

In visual GPS check the survey window, with a 2D lock you may possibly see variations up to and greater than +/- 50mtrs, when 3D lock acquired this could be up to +/- 10 mtrs, or more likely in the order of +/- 10ft, but as you may be aware you really have to leave VisualGPS running for about 1/2 hour to give an idea of average accuracy. Certainly when 3D lock acquired drift should be minimal.

But at least Visual GPS survey window will give you some idea of accuracy.

So fire your GPS up let Visual GPS run and see what happens, but obviously see if you can do this in various locations, but see what you can see. Look at the mean square average and the Least square average, but also remember the higher the DOP values the wider the results will be and lower the DOP values the greater the accuracy will be.

Forgot to ask, how often do you get this erratic behaviour ??!!

Regards

Bassrock :D
_________________
Tools: Nokia 6600, Globalsat BT 318 GPS, TTM5, +1 Wife, 2 Children, mortgage etc..

Bassrock · Occasional Visitor Joined: Sep 25, 2005 Posts: 24

Mmmmmmm

Just had a thought, in the NMEA monitor window, what NMEA words (and how many of each) do you see. ??!!!

Regards

Bassrock :D
_________________
Tools: Nokia 6600, Globalsat BT 318 GPS, TTM5, +1 Wife, 2 Children, mortgage etc..

Bassrock · Occasional Visitor Joined: Sep 25, 2005 Posts: 24

Mmmm

Further thought:-

The signal quality bar will change its colour depending if the satellite is used in the navigation solution returned by the GPGSA NMEA message. If the satellite is not used in the position fix solution, the signal quality bar will be in gray. If the satellite is used in the solution, the signal quality bar will be blue. But if they change, or signal to noise ratio drops then they may not be able to be used in the solution. Remember this is a dynamic environment and your "system" is updated once per second, so if no nav solution or partial nav solution you may also get drift.

Regards

Bassrock 8O
_________________
Tools: Nokia 6600, Globalsat BT 318 GPS, TTM5, +1 Wife, 2 Children, mortgage etc..

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