60csx Distance To Waypoint Err > Epe?

[Bikezilla]

I've noticed under some conditions I can check the "Goto" distance to a known waypoint I'm standing over to be off by quite a bit... like 45' but the GPSR's EPE shows an estimated error factor of 15'.

 

It seems to be most obvious when standing near a building... but less likely or non-existant when inside one or out in the open.

 

For example in the city, I can have an EPE of 25' but the "goto" distance for a waypoint I just, set and am standing over, can be as high as 300' Okay I'll assume this is building reflection errors... no WAAS available worst case conditions. BUT standing on my deck, directly behind my house far from the city and any other obstructions I can get a goto 45' off the mark with a EPE of half that. Even with WAAS. Another reflection issue?

 

Anyone try this?

 

It seems odd a waypoint distance can be off by numbers that far exceed the EPE.

Edited July 5, 2006 by Bikezilla

[+Team Trail Walker]

The EPE is a mysterious number and one should only use it as a good guess number. Assuming you had an error of +-25' when you set the point and an error of +-25' when you hit "Go To". Then you would add the errors to be +- 50'. Note the +-. Worst case your waypoint is 100' away.

[+Red90]

IME, that is strange. From what I have seen the displayed EPE is quite conservative that the point is within a radius of the displayed amount.

 

When marking a waypoint, it is best to have it average for short while. The overall EPE is displayed while averaging. Allow the EPE to drop to a reasonable amount. It is best to hold the GPS up so that your body (or other low objects) is not interfering with the signal.

 

When you later goto, it should be well within the displayed EPE. You should always walk away and then towards the marked location from a few directions to make sure the marked location is accurate. If you are marking for a cache location, you you spend a reasonable effort in ensuring accurate coordinates and you should then check that these are accurate.

Edited July 5, 2006 by Red90

[Bikezilla]

Doubling the distance of the EPE makes sense as a possible error (ex 10' EPE could give 20' off the mark.)

 

But there are plenty of times where it was much greater than twice the EPE.

 

Red90, thanks for the info... I'm new to GPS so could you explain how to average a waypoint? In my tests I always waited for the EPE to settle down to a constant low number.

 

Walking away from the points and coming back seemed to aggravate the errors. Out in an open field or waterfront I can get 4-0' off the mark. Standing next to a single structure things seem to get dicy, and if surounded by many fughedaboutit anything but autorouting.

[+Red90]

No it should be a radial distance.

 

Press "Mark". At the bottom of the page is a button "Avg". Left arrow over twice to get to it and press "ENTR". The "Estimated Accuracy" of the averaged location is displayed. It should decrease as long as you don't move around or cause it to get worse reception.

[+Team Trail Walker]

Thanks to Red90 for offering tips. I should have done so myself. My apologies.

 

With the 60CSx, make sure your holding it vertical. It makes a big difference. Also Waas Enabled. Latest software updates. Good luck!

[+Red90]

Oh yes, that is an important point. The 60 and 76 series lose a lot of accuracy when held horizontally.

[Bikezilla]

Tnx. I usually keep the antenna pointed in the direction of best reception during my tests. I usually find ~45 deg vertical angle works best when pointing south west (Located in southern NY) Straight up does not usually improve reception unless I exclude facing in the best direction. I'm using the latest sw.

 

I'll play with the averaging function. I will test it near a single structure some more as well.

Edited July 5, 2006 by Bikezilla

[cwichura]

You could also use an external antenna to avoid the hassles of ensuring the GPSr is held in the proper orientation. I've always preferred the external antenna -- attach it to the top of your hat/helmet and then you don't have to worry about what you do with the GPSr itself any more. Of course, you have the dork factor to worry about, but that's generally not a problem when out hiking away from civilization...

Edited July 5, 2006 by cwichura

[Bikezilla]

I tried averaging 200 samples w/ an 18-23 EPE on a city street corner

and also a 400 sample average w/an 14-18 EPE on a windowsill in the burbs, both with intermittant WAAS lock.

 

I still get goto readings ~ 43' on an 18' EPE.

 

I'll try it out in the open and see what averaging does for me.

[+hogrod]

Tnx. I usually keep the antenna pointed in the direction of best reception during my tests. I usually find ~45 deg vertical angle works best when pointing south west (Located in southern NY) Straight up does not usually improve reception unless I exclude facing in the best direction. I'm using the latest sw.

 

I'll play with the averaging function. I will test it near a single structure some more as well.

 

Seems strange, every 60/76 model I have used gets better reception held vertical. also by not holding the reciever upright you are prone to getting multipath signal(signal bounced off objects). you need to hold the unit upright and about shoulder level.

 

Also note when using the average function if you average bad data you will get an average that is way off. the best way to take an average is use the gpsr average function about 50-100times, then average the same location over 3-4days. now average all the numbers you get together. you should have great coords.

 

That being said you shouldn't have to average this way except in the worst enviroments. with my 60cx I can average coords about 50times and later when I come back to that spot I can usually get within 0-20ft. I say 0-20ft because it seems sometimes it takes the gpsr a minute to settle in and be confident of its location.(reminds me of my old meridian gold, except not slow)

[+EraSeek]

I've noticed under some conditions I can check the "Goto" distance to a known waypoint I'm standing over to be off by quite a bit... like 45' but the GPSR's EPE shows an estimated error factor of 15'.

 

It seems to be most obvious when standing near a building... but less likely or non-existant when inside one or out in the open.

 

For example in the city, I can have an EPE of 25' but the "goto" distance for a waypoint I just, set and am standing over, can be as high as 300' Okay I'll assume this is building reflection errors... no WAAS available worst case conditions. BUT standing on my deck, directly behind my house far from the city and any other obstructions I can get a goto 45' off the mark with a EPE of half that. Even with WAAS. Another reflection issue?

 

Anyone try this?

 

It seems odd a waypoint distance can be off by numbers that far exceed the EPE.

 

 

When checking your postion check the marked coordinates with your current coordinates. They may match but you can still have a goto that is way off if you are near a road and have "Lock on Road" engaged. I have had that happen before. So just turn off "Lock on Roads" and your Goto should pop right back to normal.

[Bikezilla]

Thanks folks.

 

Yesterday's and today I've been holding the GPS vertical near shoulder height, and will stick with that method. (didn't seem to help in that case)

 

I also tried this morning on the train platform, which is way out in the open on the riverfront. Not unexpectedly I got good results of 2-4' with 5 walkaway and goto-walkback tests frome several directions.

Avg 100 samples, EPE 13' WAAS locked, 10 sats most full strength.

Of course this is a near best case condition.

 

I will try near the house and in the city with the "lock on roads" disabled and see what I get.

Thanks!

[+Red90]

I assume you are routing "Off Road". That is all I can think of as I have never seen this.

[Bikezilla]

Red, are you recommending I set the GPSR to "Off Road" as well as disabling "Lock on Roads"?

Do I need to have R.O.R. set when locating benchmarks, waypoints etc?

Does ROR by default disable LOR?

 

BTW, I'm Heading out at lunchtime to test in lower Manhattan I'll play with those functions.

 

-BZ

Edited July 6, 2006 by Bikezilla

[+Red90]

If you route on roads, the GPS will try and make you stay on a road. To GOTO a waypoint, you must do the final part of the routing in "Off Road" mode or it will alway try and make you go to the nearest road and not the waypoint.

[Bikezilla]

Tnx.

 

Not to belabor the questions but,

 

It sounds like a lot of deep menu setting changes are needed to transition from vehicle autorouting/street navigation to walking it out to the actual waypoint.

 

Are all the following steps required?

1)Disable "Lock on Roads" in the Maps setup menu

2)Set Guidance method to "Off Road" in the Routing setup menu

AND

3)Set "Pedestrian" in the Calculate Routes for menu in the Follow Road Options in the Routing setup menu.

 

If so, a macro or 2nd profile function would really be nice!

 

One more question, what does the "Off Road Transition" function on the Saved Routes options menu do?

[+hogrod]

I leave "lock on roads" enabled 99% of the time.

 

if you are doing a goto and using the "follow road" option, when you get to the cache area you just need to hit menu from the compass or map screen and select recalculate. you will then be asked "follow road" or "off road"

 

choose offroad, its that easy.

[Bikezilla]

Nice. I'll try it both ways now and report back later.

Thanks for all the help!

[+Red90]

Lock on roads should not affect anything, as far as I know. It is just the routing. Set is to "prompted" in the routing setup.

 

From the map page, hit menu, then recalculate when you get out of the car. Choose off road at that time.

[Bikezilla]

I tried it both ways at a few different locations. I even averaged the waypoints >50 2x

When in town, with buildings around the distance to the WP was usually more than 2x>EPE (the EPE was <18' no WAAS lock)

 

When on the waterfront away from the buildings the distance to the WP was 2-4' W/ WAAS locked.

The worst case sinereo WP on a street w/ skyscrapers on both sides, in front of a building doorway, was over 150' off even with a EPE of 20'

 

Last test will be on my windosill and on my deck out in suburbia.

On/Off Road seems to me to only affect how it is routed to the WP but I did not see a difference in the distance to WP. I'll keep experimenting.

Edited July 6, 2006 by Bikezilla