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tracking problems
June 27, 2012
6:21 am
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phild31
Nashua, New Hampshire USA
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All I can give you is anecdotal evidence; A hunting buddy and I were heading out on an old logging road in northern Maine last year.
He had his old explorist 400, I had my 710.
We walked a little over a mile side-by-side creating a track on each unit.
When we split up we agreed to meet there and hike out together at the end of the day.
While we were walking out that evening we compared our respective tracks.
The 400 was consistently 50 feet off the road and the 710 was consistently within 20 feet of the road.

Make whatever you will of that but that's what I saw in a direct comparison of the two units in the field.
On the map on my laptop back at camp the two tracks looked about the same as what they seemed in the field but the old logging road is not on the map so on the map I have no idea which was on the road but both were never far enough off it in the real world to be a problem.

When in trouble or in doubt, run in circles, scream and shout

June 27, 2012
5:38 am
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k-rok
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just trying to come up with an answer, i know it's far fetched but i was just trying to figure out why the old 400 was much better, i have compared the 2 using the same track logs on Google Earth and the 400 wins every time.
i have read about the Starfire III (think that's the name) not allowed to be used as a satt. lock system on the new Magellan's because of a lawsuit but they claim to have it.

June 24, 2012
4:12 pm
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phild31
Nashua, New Hampshire USA
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The technology keeps improving but even 12 years ago you could buy a GPSr for under $200 that fits in a shirt pocket with accuracy to 30-40 feet!

The real improvements in consumer GPS receivers is in data handling and accurate maps on the units. (thank you Sockeye & your brethren)

As far as accurate points and tracks, with the new antennas for handheld units the signal acquisition has improved, so we can expect on average to have an accuracy of 20-30 feet anywhere.

But if you want no oddball points on a track have it make a point only when you move, then you will have what looks like deadly accurate tracks but when you examine the track you will see that it made very few points, so it cut corners when it didn't detect enough movement.

The new units are not less accurate, just the opposite, plus they can make a point every 5 seconds to give you a very accurate track.
Because of the number of points created, every now and then you will get a point created when the signal was temporarily blocked but what's the big deal?
You see one point 200 feet off the road, you know it's an anomaly right?

Before the "great blue switch" controlling selective availability was pressed in May of 2000 the accuracy of my cheap old unit was about 300 - 400 feet!
I had been using a Garmin gps12 GPSr for a few years for hunting, hiking & exploring.
It was very nice having a breadcrumb trail to find my way back and waypoints for places deep in the woods, even with the waypoints and tracks being up to 400 feet off.

At the time the military used the excuse of bad guys shooting missiles at us to keep the satellite signal encrypted.
Basically, President Clinton told them 500 feet - 30 feet is all the same with a-bombs!
But accurate gps data will be invaluable for police, fire departments, rescue, ambulances, boaters, etc so decrypt the signal!

Now we have farmers in Iowa plowing perfectly straight furrows, shipping companies cutting delivery times & costs, spoken driving directions for anyone to anywhere and my iPhone telling me where the nearest Tim Horton's is, all because of cheap accurate GPS technology.

Oh yeah, plus we have Geocaching! :woohoo:

When in trouble or in doubt, run in circles, scream and shout

June 24, 2012
4:55 am
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David
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We have a member in the church here, who until the death of the California economy a couple of years ago, worked for a heavy construction company that builds highways and roads and he was telling me about the GPS units that are in the graders. With the new technology all of the blade adjustments for the levels and everything else is controlled by a computer which is basically guided by the GPS and then machines are extremely accurate; but then again, they're also extreme expensive...

In actuality the accuracy of even the cheapest consumer grade GPSrs is scary. When I was working for the NSA we were told of an experiment that was done. A couple of brainiacs were given something like $200k to create a delivery system for a war head and they had to use off the shelf items. With that money they were able to purchase a run don’t old Cessna that would fly, but couldn’t pass the required FAA inspections or guidelines and with a laptop computer and a GPS, of course with several other items, were able to rig the aircraft up to be taken off via remote control and then deliver its payload to an exact location under the guidance of the laptop and GPS. When they actually tested it, it did deliver the mock weapon to within 12’ of the target coordinates…

Not really that cool!!!

David


 

 

 

June 23, 2012
3:37 pm
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phild31
Nashua, New Hampshire USA
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Try not to get carried away with expecting deadly accurate GPSr data.

No handheld consumer GPSr has ever been "deadly accurate" and it has nothing to do with the potential to aim missiles, the units are just not capable of it.
Get yourself a $2500 - $6000 professional quality unit and you will have "deadly" accurate tracks and points.
Of course it will have a bigger antenna, much more powerful processor and won't be quite as portable.
By less portable I mean it weighs several pounds, antenna is two feet long, it does not run on AA batteries and it's mounted in a backpack.

The military does not use consumer grade GPSr to aim missiles, the units they arm the soldiers aiming missile strikes with costs thousands of dollars.
But the standard issue GPSr issued to every soldier would be closer to a consumer grade unit because every soldier does not need pinpoint accuracy to just find their way around.

Just like us!

For an anecdotal example, I met a professional surveyor marking property boundaries in New Hampshire this winter.
He was using a $4500 unit carried in a backpack with a large antenna that averaged waypoints to within 2 feet!
He was interested in the capabilities of my 710 and was quite impressed with it.
His personal GPSr is a 7 year old Garmin and he said he's now going to look into getting a new unit for himself.

When in trouble or in doubt, run in circles, scream and shout

June 23, 2012
3:49 am
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k-rok
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Thanks P. looks about right, it's not that big a deal to fix the track but i had an old Magellan 400 and never had a problem with it, deadly accurate, never had to fix one point. that's why i can't figure out why the GPS has become less accurate.

i may have just answered my own question, if you where going to launch a missile from a standing position wouldn't it be great if the GPS coordinates where all over the place.

i know that travelling along any road in a truck that i have a point way out side the road once in a while.

June 14, 2012
2:05 am
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phild31
Nashua, New Hampshire USA
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BTW, I have tested 5 Garmin, 3 DeLorme and 6 Magellan GPS receivers, all different models and they all do the same thing.

Here's some screenshots of my GC and 710.
I had them sitting in the window of my living room for 15 minutes.
.

When in trouble or in doubt, run in circles, scream and shout

June 14, 2012
1:48 am
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phild31
Nashua, New Hampshire USA
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One of the problems with consumer grade GPS receivers is what's called DOP (Dilution Of Precision).

There are many factors affecting the accuracy of GPSr and the cheaper (under $2,000) receivers can't cope with them all, so the software adjusts for estimated accuracy.
But the estimated accuracy is an educated guess at best.
When you are moving the device can eliminate some of the factors, like interference of the signal.
But when you stop the signal changes because the satellites are moving and changing the signals to the unit, even though it's indicating good satellite signal.

In other words it seems to be an inherit problem, to some degree, with all consumer grade GPS receivers.
I've always had to edit my tracks if I stayed at one spot for more than 10 - 15 minutes.
Both my GC and 710 have always behaved this way & have not gotten any worse over time.

An interesting web site I found is this - GeoDrift.

The Background Information link on the GeoDrift page explains the issue in more detail.

When in trouble or in doubt, run in circles, scream and shout

June 13, 2012
9:26 pm
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k-rok
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i have to correct every track i make in vantage point. it started about a year ago and is getting worse. i have points that are anywhere from 100 to 1000 yards from my position that i have to correct.

i finally figured out it happens every time i stop, as long as i'm moving everything is ok.

i have tried using auto, distance and time but it's still the same. i am also getting 5 bars for sat contact at all times.

is the GPS on it's way out or is there another reason for this.

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