Three GPS' at same point on ground.

I ground truth'd 3 GPS' today:

1. AMOD photo tracker (20 channel Sirf III with WAAS)
2. Garmin etrex 30 ( ? channel, GPS/WAAS + GLONASS ).
GPS was "D" at time of check.
3. iPhone 4.

etrex 30: 6.58 m
Photo tracker: 4.85 m
iphone 4: 3.53 m

So, for once, the iPhone beat "real" GPS's - though the amount was trivial.

In other areas (esp. in the woods) the etrex and photo tracker were 10 -
15 metres apart on some trail segments. (No ground truths to test
against), I didn't record for the iPhone on those segments.

No conclusion other than you can never trust GPS in the woods and

"A man with 3 GPS' doesn't know where he is."

--
"I see!" said the blind man as he picked up his hammer and saw.

On 12/11/2011 12:16 PM, Alan Browne wrote:
I assume this was without averaging.

I took the GPSMAP60 out to a reference point and got it to 4ft accuracy.

The emap was dear in canyons with heavy canopy. The helix on the
GPSMAP60 works under the same conditions, but the tests were don't at
different times. I think the quad helical is better than the patch if
you don't mind the size.

On 2011-12-11 18:03 , miso wrote:

Not invoked. But from the Garmin's 5 second interval sampling there is
some filtering such as a moving average and minimum distance traveled.
I wish it was unfiltered so I could see what was going on - as I can
with the photo tracker.


In deep canyons or heavy forest I don't trust the horizontal with
consumer handhelds for any great accuracy - esp. if there's a likelihood
of multipath. Some years ago (late 90's) I had brief access to a
differential kinematic (not RT) system (recorder in backpack + recorder
at arbitrary reference). I didn't do any ground truths with it, but the
plot through the woods (post processing) was very clean and walk backs
were sub metre from the walk in. Wish I had that now.

--
"I see!" said the blind man as he picked up his hammer and saw.

On 12/11/2011 3:15 PM, Alan Browne wrote:
Make that the emap was deaf. Fat finger typo!

The reference spot I use is in a canyon, but no canopy. I'll have to
check how many birds it got.

This is a blast from the past:

Emap uses a patch. GPSMAP60 a helix. But different chipsets.

On 2011-12-11 22:51 , miso wrote:

That's fine for units with external antennas. A choke ring antenna may
be better in canyons (I'm not sure). (And the choke ring can likely
support helical or patch antennas). But they're big mothers.




--
"I see!" said the blind man as he picked up his hammer and saw.