Itsme Posted June 7, 2002 Share Posted June 7, 2002 I noticed the following problem while using my Garmin etrex venture. I compared the value displayed by "Trip Odometer" (Trip computer Page) with the value displayed by my cycle computer. As long as i'm travelling in "open" area the 2 values are perfectly similar. However, as soon as i enter a more tree-covered area the value displayed by the GPS significantly starts to differ from my cycle computer (and other resources confirm that the cycle computer is absolutely right). The difference is really significant and is often 25% or more). Strange thing is that the satellite page displays that enough satellites are received, also the dotted line (breadcrump) that indicates the path of travel shows no interruption at all !! In other words: all indiactors show "normal" operation but the information displayed is absolutely not correct. As soon as i enter more open area, the GPS and the cycle computer return to perfect similarity. My question: how is such a significant difference possible and can i do something about it? Thanx in advance, Jack. Quote Link to comment
+Olar Posted June 7, 2002 Share Posted June 7, 2002 Jack I'm just taking a wild guess here. Does your route involve a lot of hills? Your bike's odometer would read actual ground distance travelled while the GPS would only record horizontal distance. I'm no mathematician so I can't say what difference would accumulate over a certain distance. Food for thought. Cheers, Olar Quote Link to comment
+Hawk-eye Posted June 7, 2002 Share Posted June 7, 2002 Another thought ... while your signal might not be lost ... your accuracy will vary. Things like reflective signal, sat. geometry, and varying EPE could give you these variations. Just a thought ---------------------------------------------------------------- Co-founder of the "NC/VA GEO-HOG ASSOCIATION" ... when you absolutely have to find it first! Quote Link to comment
Itsme Posted June 9, 2002 Author Share Posted June 9, 2002 Thanx for your suggestions. Since i live in Holland (as flat as a pancake) the reason probably won't be the difference in height :-). If difficult receiving reports such inaccurate results (without any clue) GPS seems unusable for measuring speed and distance. Do any have you have (good or bad) experiences on this subject? Thanx again for your replies ! Quote Link to comment
peter Posted June 9, 2002 Share Posted June 9, 2002 You may well be dropping in and out of satellite lock despite the good indications on the satellite page. When I completely block the antenna on my GPSr, it still takes a few seconds for the bars indicating signal strength to drop to zero. And the alarm for lost lock only comes after 30 seconds without a signal during which time the tracklog is continuing to show movement based on how fast I was going when the signals were lost. The trip odometer on different models and firmware releases acts differently when there is intermittent loss of lock. On earlier firmware versions of my eMap the mileage would not increment at all during periods without satellite lock while the current version adds in the straight-line distance covered once satellite lock is restored. Quote Link to comment
+SteelyBob Posted June 10, 2002 Share Posted June 10, 2002 A buddy of mine purchased an eTrex Legend and had a good time finding caches in central Mass. He's been with me a couple of times as well. But when he got home to Southern New Jersey suddenly he was unable to find any caches. He says that he can be watching his location on a map, while standing still and the Legend will report that he's moving! The track-line actually marches up the screen and across roads and rivers. Has anyone else seen this? Quote Link to comment
+apersson850 Posted June 12, 2002 Share Posted June 12, 2002 quote:Originally posted by SteelyBob: He says that he can be watching his location on a map, while standing still and the Legend will report that he's moving! The track-line actually marches up the screen and across roads and rivers. Has anyone else seen this? He hasn't by any chance turned on the Demo mode, where the unit simulates movement, for demonstration purposes where no signal is received (e.g. inside a shop)? Anders Quote Link to comment
+worldtraveler Posted June 12, 2002 Share Posted June 12, 2002 quote:Originally posted by SteelyBob:...while standing still and the Legend will report that he's moving! The track-line actually marches up the screen and across roads and rivers. Has anyone else seen this? If you're in a location where you're getting a lot of reflected signals (dense tree cover, tall buildings, etc.), the screen will show you as moving all around as it continually recalculates your position based on the fluctuating signals your GPSr is receiving. It is most noticeable when your screen is zoomed way in. Worldtraveler Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.