Distance discrepancies with my eTrex

[+LobaSeattlense & The Simonator]

My eTrex Legend tends to show the distance as shorter than it really is. Has anyone else run into this problem?

 

Eireann

 

"Eagles may soar, but weasels don't get sucked into jet engines"

"Dale Lobo" y "Vamos Gimnasia"

[+mrp]

There are several different distances you could be talking about, I'll try to give an answer to several of them...

 

If you're talking about distance along a track, or about the trip odometer, then the reason is most likely because when the gps is cutting corners, literally. They both measure the accumlated distances between the points measured. In the case of the odometer, this is usually pretty close to the actual mileage, since it takes a measurement of your position every second or so (unless you have spotty coverage, or have the battery saver feature on). With good reception (and without battery saver on), I typically find that these errors are less than 1%. (That can still be 2 or 3 miles over a road trip.)

 

In the case of tracklogs, fewer (sometimes much fewer) points are looked at, and therefore the errors are larger. A saved tracklog only has about 20-50 points, whereas the active tracklog can have up to 10000, but they're often taken 15seconds to a minute apart (depending on settings). In this case a large loop of road may be completely lost, and these little errors accumlate into big errors over time.

 

If you're getting errors in the distance to a waypoint... well.. 30 ft. off is typical, 60 isn't unheard of in some cases, but big errors (100's of feet or more) usually idicates other problems.. (transcription errors, wrong datum, etc) and huge errors are usually due to something like multipath reception (receiving a reflected signal, rather than straight from the satellites)

 

Does this answer you question? :-)

 

-- Mitch

[+LobaSeattlense & The Simonator]

I should have been a little more specific. What is happening is that my GPS says that from my house to a friends house is 7.8 miles, I know it is farther than that. The GPS also says that Florida to Seattle is only like 2700 miles, in reality it's like 3000.

 

Eireann

 

"Eagles may soar, but weasels don't get sucked into jet engines"

"Dale Lobo" y "Vamos Gimnasia"

[peter]

quote:

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Originally posted by LobaSeattlense & The Simonator:

What is happening is that my GPS says that from my house to a friends house is 7.8 miles, I know it is farther than that. The GPS also says that Florida to Seattle is only like 2700 miles, in reality it's like 3000.

---

 

Your GPS is giving you the direct great-circle distance, i.e. "as the crow flies." From Miami to Seattle is just over 2700 miles but of course the driving distance will be longer since no roads lead straight from one city to the other. Only units that calculate a route for you, like the GPS V, can make an estimate of the driving distance.

[+GeckoGeek]

quote:

---

Originally posted by LobaSeattlense & The Simonator:

I should have been a little more specific. What is happening is that my GPS says that from my house to a friends house is 7.8 miles, I know it is farther than that. The GPS also says that Florida to Seattle is only like 2700 miles, in reality it's like 3000.

---

As pointed out the GPS will give "as the crow flys" distance. Since we're not crows, we tend to walk a crooked and therefor longer path.

 

But you should also check to make sure your unit is set for the right units - statute and not nautical miles.