Baller Phil2360 Posted November 6, 2012 Baller Share Posted November 6, 2012 Just Back from my 3km morning walk. Always carry my Garmin Etrek with me to monitor pace & occupy my mind. The first km is usually averaged out at 5.6km/h & by the end of the 3km the average is usually 6.0km/h. Added an extra block at the end this morning, so total distance I was expecting was about 3.2 to 3.3km, I was pretty much on target for this figure as I approached my back gate but when I looked again moments later my total distance had jumped to over 3.8km & average was now 7.0km/h. I've done this for years & know about GPS errors, but it instantly got me wondering if this at all related to some of the Perfect Pass issues we see. Have now only had 3 weekends on the water this season & PP performed spot on during the first two outings. On the third, we experienced 2 instances of the PP losing it during a run. Giving I've just seen this 500m error It's got me thinking that a similar GPS error whilst PP is in control could be responsible for some of the random problems people see. Cheers Phil Link to comment Share on other sites More sharing options...
Baller thager Posted November 6, 2012 Baller Share Posted November 6, 2012 I've gotten oddball ZO dropouts also. Link to comment Share on other sites More sharing options...
ToddF Posted November 6, 2012 Share Posted November 6, 2012 I have gotten weird readings from my Gps putting me on a near by road when I am on a trail. That usually gives me extra distance because it jumps back and forth trying to figure out where I am at, Measure it on google earth to get an accurate measurement. I imagine that they do lose a satellite occasionally and that messes with the timing Link to comment Share on other sites More sharing options...
Baller MattP Posted November 7, 2012 Baller Share Posted November 7, 2012 Our ZO usually picks up at least 9 satellites at a time. I don't think loosing 1 would change anything. All you really need is 3? Link to comment Share on other sites More sharing options...
Baller colo_skier Posted November 7, 2012 Baller Share Posted November 7, 2012 From what I've read/seen the issue is actually due to trying to reject aliasing errors from any of the primary satellites being used to calculate the speed vector. Link to comment Share on other sites More sharing options...
Baller eleeski Posted November 7, 2012 Baller Share Posted November 7, 2012 My aircraft gps specifies 15m accuracy. Nowhere near good enough for waterskiing precision. I was very sceptical about the ZO claims. Stan's MC had ZO and PP with magnet timing. Timing the boat with both systems on gave times that matched well with .01 discrepancies. ZO is accurate. How can this be? Often ZO will beep early or late by a noticeable amount. But that error is consistent - entry gates are as off the same direction and magnitude as exit gates. Whatever dithers the signal does not change over the small distance or time interval of the course. Trust the ZO. Drivers need to carefully monitor ZO. My aircraft gps lost signal - once. ZO will screw up one or two rides a tournament, but driver technique causes many of these. The gps error warning on ZO is not aggressive enough - a serious deficiency. Fortunately ZO is so reliable that it is not a real problem. ZO rocks! Eric Link to comment Share on other sites More sharing options...
Baller Phil2360 Posted November 7, 2012 Author Baller Share Posted November 7, 2012 @rico. No weather anomalies, so think I could rule that out, wouldn't blame reflections or multi-pathing errors either as I've walked this route 100's of time over recent years. so could only be somthing atmospheric, solar or maybe a bit of rogue data from a sat. Link to comment Share on other sites More sharing options...
Baller jackski Posted November 7, 2012 Baller Share Posted November 7, 2012 Eric, this was expalined to me by some one much smarter then me. There are two GPS signals sent from the satellites. The most commonly used is the positioning one to find where you are on the earth and you are correct it's not very accurate although I was told it can be within three feet. The second is a time/distance based signal which we use to control the actual speed. It's accurate but dosen't know where it is, just how far it has gone from the setpoint. The reason the beep is not always in the same spot is that the speed control uses the positioning signal to locate the course, and it is only accurate to at best the three feet mentioned above. Link to comment Share on other sites More sharing options...
Baller colo_skier Posted November 7, 2012 Baller Share Posted November 7, 2012 Was there a high sided truck anywhere near you on the particular failure day? Was it raining? Link to comment Share on other sites More sharing options...
Baller Phil2360 Posted November 7, 2012 Author Baller Share Posted November 7, 2012 @colo_skier, Nothing like that. Watched closer this morning, & saw average jump to 6.7km/h in the first 50m. After that I watched the moving speed a fair bit. Set a steady pace that flicked between 5.7 & 5.8km/h & noticed every few minutes that it would jump to numbers like 6.1 to 6.6km/h. Unit has 1 second updates by the way, & when seeing these deviations, which typically lasted 2 or 3 seconds, I could not identify any significant environmental changes or significant structures that could expain the variations. Might dig this out again & have a bit of a play, haven't used it in nearly 10 years, but did find it a bit interesting at the time. http://gpsinformation.net/main/sawatch.htm http://www.huntting.com/sawatch/ Cheers Phil Link to comment Share on other sites More sharing options...
Baller Phil2360 Posted November 12, 2012 Author Baller Share Posted November 12, 2012 Interesting on Sunday. Two non engaging runs. Wasn't driving so not sure what was happening, but... On the 25km drive back to town I could not get my TomTom SatNav to get a fix despite turning it on & off several times. Interestingly a few hours later the TomTom grabbed Satellites straight away when I turned it on again. Maybe there's some rogue data coming from one of the satellites ATM & causing issues when it's in view. Link to comment Share on other sites More sharing options...
east tx skier Posted November 13, 2012 Share Posted November 13, 2012 I had a GPS antenna on SG go out at the beginning of the year. Replacement antenna works much better than the original ever did. Link to comment Share on other sites More sharing options...
Baller Phil2360 Posted November 15, 2012 Author Baller Share Posted November 15, 2012 Interestingly, My GPS had been spot on the last few mornings, total distance always about 3.12km, until this morning when it jumped twice. About 500m each time, to give a total distance of over 4 km. East Tx, I guees you do realise that that's not just the antenna, but the complete GPS unit, so any thing could have been possible as far as faults are concerned. Cheers Phil Link to comment Share on other sites More sharing options...
east tx skier Posted November 15, 2012 Share Posted November 15, 2012 @Phil2360, by antenna, I should have said the "Garmin puck." I sent it back to Perfect Pass around April 2012. Perfect Pass bench tested it and determined it to be dead. Replacement puck functions better than original did new. Link to comment Share on other sites More sharing options...
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