Legend HCx gross inaccuracy

[+John H Watson]

Software is 2.40/2.40, so it's not likely related to the issues with 2.60/2.60.

 

This only happened once, and I'm wondering if it's "multipath". I'm not experienced enough to recognize this. The gritty details:

 

1. I was literally sitting on a cache location in a city park surrounded by buildings mostly about 5 stories tall. City Navigator showed the streets and accurate cache location. However....

 

2. The HCx showed me as standing in the next block, some 300' away. It reported an accuracy of ~15 feet.

 

3. Walking toward where the HCx showed as my location in the next block showed minimal movement on the unit.

 

4. Powering the unit off/on initally brought my location closer to where I actually was (like 40' away...), but my position slowly drifted back across the street onto the next block.

 

5. At all times signal strength was excellent, with 8 or so satellites registering. No tree cover.

 

So... What happened?

 

Thx.

Edited July 15, 2008 by John H Watson

[+anndeefam]

My Legend HCx does not like the city very much, I'm able to find coords I'm looking for but does act bit crazy occasionally. Once my HCx showed my at a location half way across the state everything was out of sync. I re booted and all was fine and back to normal, except ten minutes later my batteries went dead. Possible low batteries could be causing some odd symptoms to occur. Also I can tell you the the Legend HCx likes to be moving fast it seems that the faster it is moving the more acurate the pointer is. Slow walking = slow pointer I've learned to slow down with it. All that said I love this unit and would advise anyone to purchase one.

[+gpsblake]

Do you have LOCK TO ROAD turned on? That could be the problem.

[+John H Watson]

Do you have LOCK TO ROAD turned on? That could be the problem.

 

No, using it strictly in "off road" mode. It didn't show me as on the road, tho. I was indicated as being in the middle of the next block.

 

I wasn't looking at the compass display, as I was moving very little. I had it on the map page. It shows my "location" (if you can call it that.....) as an "accuracy circle" (my made-up term), which was entirely across the street.

 

This was in a quieter area of downtown Portland. In the middle of the urban jungle, I was getting surprisingly good position results.

[MtnHermit]

I believe that your multipath conjecture is the most plausible answer. One of the "law of unintended consequences" from the very sensitive chip in the H family.

 

Seems to me you could set up a test near similiar buildings at a different location, see if you can replicate the error.

[+John H Watson]

I believe that your multipath conjecture is the most plausible answer. One of the "law of unintended consequences" from the very sensitive chip in the H family.

 

Seems to me you could set up a test near similiar buildings at a different location, see if you can replicate the error.

 

This was the only significant error that I found in 2 days of urban caching. Usually my position was spot on in reference to the CN maps, or else the "(in)accuracy circle" was large enough to cover my real position.

 

I don't know if batteries may have been an issue. They pooped out after perhaps another 2 hours of use.

[MtnHermit]

I don't know if batteries may have been an issue. They pooped out after perhaps another 2 hours of use.

When the batteries on my eTrex are low, the tracklog will show large (100-1000 feet) random excursions, totally off my path. So possible. Again, another test is possible.