Garmin etrex HCX inaccurate ?

MighyG

New Member
Went out on a 60 mile ride today along a canal towpath almost all the way. Got back and downloaded my tracklog, then uploaded it to gpsies.com (and mapmyride). Both sites showed that the garmin had gone way off course a lot of times, defaulting to a road which was about 100ft from the canal path.

The HCX gps receiver even works in my house, so for the life of me can't see why it would be creating such errors outdoors. Also the fact it keeps jumping to a road is a bit suspicious (is there some algorithm or setting that makes it use roads as defaults when its not sure where it is??)

Any help / info appreciated

thanks


paul
 
OP
M

MighyG

New Member
just found a setting on it called 'lock on road' which was on, wondering if thats what has caused it. have now turned that off so will see if it makes a difference

:evil:
 

andrew_s

Guru
Location
Gloucester
It will have been the problem.
Lock on road is there for use in towns where there are a lot of position errors due to signals reflecting off tall buildings. If it's working in follow road navigation (i.e. satnav fashion), it can get confused.
 

battered

Über Member
Lock on road is certainly your problem. The thing works by triangulating 2 satellites which orbit the equator at however many miles. The difference between the measurements is used to calculate where you are using trigonometry. So the thing is masuring the distance to satellites miles above the equator and you are bitching about 100 feet?

Joking aside the GPS is doing a pretty decent job and the lock to road setting is just to give it a clue if its calculations across hundreds of miles show up a 50yard error.

Oh, and it's not making mistakes. :-)
 

jimboalee

New Member
Location
Solihull
battered said:
Lock on road is certainly your problem. The thing works by triangulating 21 satellites which orbit the equator at however many miles. The difference between the measurements is used to calculate where you are using trigonometry. So the thing is masuring the distance to satellites miles above the equator and you are bitching about 100 feet?

Joking aside the GPS is doing a pretty decent job and the lock to road setting is just to give it a clue if its calculations across hundreds of miles show up a 50yard error.

Oh, and it's not making mistakes. :-)
Corrected your typo error.
 

jimboalee

New Member
Location
Solihull
Untoggle the 'lock on road' facility and notice a blue circle around the cursor.
No, you are not covered in concrete, this is the estimated error.

Go for a ride in town between some tall buildings and watch the circle widen. Watch out though, try to keep an eye on the road and traffic.
Where two roads are close together, the circle may envelope both roads. If you was on 'lock on road' the cursor may display a dancing act between the two roads as the positioning software changes its mind.;)
 

PpPete

Guru
Location
Chandler's Ford
Even with the lock on roads switched off you may very occasionally find the track has drifted off for a few seconds (or even minutes)
Funny thing is when it "realises" it's off, and jumps back to where you really are.... you get a spike in the speed that is often totally unrealistic.
Happened to me once in a years usage in a long distance pedestrian event, and according to the track I was running @ 30 mph for a few seconds (after already covering 20 + miles) . Usain Bolt had better watch out.
 
OP
M

MighyG

New Member
thanks for the comments, my expectations had been raised to perhaps an overly optimistic level by getting a signal in the middle of our house, so didn't think it would ever struggle outdoors
 

marinyork

Resting in suspended Animation
Location
Logopolis
MighyG said:
thanks for the comments, my expectations had been raised to perhaps an overly optimistic level by getting a signal in the middle of our house, so didn't think it would ever struggle outdoors
You get a few hills where it blasts the accuracy down. I've tried GPS on a canal near here and devices aren't too happy with some.
 
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