Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

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Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

Sebastian Arcus
I was looking at the eTrex series from Garmin to use for mapping on OSM,
as they seem to be robust, compact and have specially long battery life
(25 hours on 2 AA batteries). The main difference between 20 and 30
seems to be that 30 has altimeter and compass, while 20 doesn't have
them. Is this important when recording GPS tracks to use for mapping on
OSM? Doesn't compass and altitude data come from GPS satellites anyway?
Or an internal altimeter and compass are more accurate?

If anybody here has either of the above GPS units and uses them for
mapping, it would be useful to hear a first hand opinion.

Thanks,

Sebastian

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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

Dudley Ibbett
I don't have the etrex but I do have a garmin 62s with the compass and barometer altimeter.  I have never used either for mapping.   There is contour data available in the UK so there doesn't appear to be the need for elevation data.

There are other reasons you might want them.  Traditionally  barometric altimeters were also used to give you an idea of changing weather conditions.  I guess you could use the compass to take bearings of an object you wanted to map but could't get to but a Silva type compass would probably be easier to do this with.

Regards

Dudley




Sent from my iPad

On 30 Jan 2013, at 21:35, "Sebastian Arcus" <[hidden email]> wrote:

> I was looking at the eTrex series from Garmin to use for mapping on OSM, as they seem to be robust, compact and have specially long battery life (25 hours on 2 AA batteries). The main difference between 20 and 30 seems to be that 30 has altimeter and compass, while 20 doesn't have them. Is this important when recording GPS tracks to use for mapping on OSM? Doesn't compass and altitude data come from GPS satellites anyway? Or an internal altimeter and compass are more accurate?
>
> If anybody here has either of the above GPS units and uses them for mapping, it would be useful to hear a first hand opinion.
>
> Thanks,
>
> Sebastian
>
> _______________________________________________
> newbies mailing list
> [hidden email]
> http://lists.openstreetmap.org/listinfo/newbies

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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

St Niklaas
In reply to this post by Sebastian Arcus
Hi Sebastian,
 
I didnt bought a Etrex last year, but did some study. I decided to buy a 62s, since it has a compass and accurate grid scan. And Im able to look at a colorized map, I like to use it for hiking and cycling.
So I would advice you to get one with a compass, since it reacts the normal way at a change without satelites. I dont have any idea about your budget, but that has to be a factor too.
Another advance is the possible use of rechargeble and through away batteries, since I wont be able to load them very well on a tour and the other batteries can be bought almost everywhere.
I hope you can find your way around, there have been some talks about GPS machines around here.
 
Greetz
 
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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

Craig Wallace
In reply to this post by Sebastian Arcus
On 30/01/2013 21:33, Sebastian Arcus wrote:

> I was looking at the eTrex series from Garmin to use for mapping on OSM,
> as they seem to be robust, compact and have specially long battery life
> (25 hours on 2 AA batteries). The main difference between 20 and 30
> seems to be that 30 has altimeter and compass, while 20 doesn't have
> them. Is this important when recording GPS tracks to use for mapping on
> OSM? Doesn't compass and altitude data come from GPS satellites anyway?
> Or an internal altimeter and compass are more accurate?
>
> If anybody here has either of the above GPS units and uses them for
> mapping, it would be useful to hear a first hand opinion.

Just about any GPS device can use the GPS satellites to get the
elevation. With modern GPS devices with high sensitivity receivers, this
is usually pretty accurate.
The barometric altimeter is supposed make the elevation more accurate.
It may help a bit if you have poor GPS reception, eg under trees, or in
a canyon or between tall buildings. But the altimeter can be affected by
changes in air pressure or weather. Its debatable as to whether it
actually helps much.

For a compass, if you are moving then the device can figure out your
direction from the GPS satellites. But this doesn't work if you are
stopped. So a compass is handy if you walk up to a junction, then stop
and check which way your GPS is pointing.
Though even without a compass, you don't have to move very far for the
GPS to point the right way, about a metre or so should do. So you can
probably manage without this (unless you are trying to navigate at the
top of a cliff).

So the altimeter and compass don't really matter for OSM mapping.
Elevation data is not usually added to OSM, so it doesn't matter whether
or not your GPS tracks contain accurate elevation data. And the compass
direction is not recorded in the track anyway.

Personally, I would say just get the Etrex 20, as it is a bit cheaper.

Craig

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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

Cartinus
In reply to this post by Sebastian Arcus
Hello,

I first used a (loaned) Garmin GPSmap 60Cx (without compass and
altimeter) and then bought a GPSmap 60CSx (with compass and altimeter).
I never use the compass or the altimeter for mapping, but the extra
features have a noticeable negative effect on battery life.

So if I had a do over, then I'd buy the one without the compass and
altimeter.

On 01/30/2013 10:33 PM, Sebastian Arcus wrote:

> I was looking at the eTrex series from Garmin to use for mapping on OSM,
> as they seem to be robust, compact and have specially long battery life
> (25 hours on 2 AA batteries). The main difference between 20 and 30
> seems to be that 30 has altimeter and compass, while 20 doesn't have
> them. Is this important when recording GPS tracks to use for mapping on
> OSM? Doesn't compass and altitude data come from GPS satellites anyway?
> Or an internal altimeter and compass are more accurate?
>
> If anybody here has either of the above GPS units and uses them for
> mapping, it would be useful to hear a first hand opinion.


--
---
m.v.g.,
Cartinus

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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

Sebastian Arcus
On 31/01/13 05:35, Cartinus wrote:

> Hello,
>
> I first used a (loaned) Garmin GPSmap 60Cx (without compass and
> altimeter) and then bought a GPSmap 60CSx (with compass and altimeter).
> I never use the compass or the altimeter for mapping, but the extra
> features have a noticeable negative effect on battery life.
>
> So if I had a do over, then I'd buy the one without the compass and
> altimeter.
>
> On 01/30/2013 10:33 PM, Sebastian Arcus wrote:
>> I was looking at the eTrex series from Garmin to use for mapping on OSM,
>> as they seem to be robust, compact and have specially long battery life
>> (25 hours on 2 AA batteries). The main difference between 20 and 30
>> seems to be that 30 has altimeter and compass, while 20 doesn't have
>> them. Is this important when recording GPS tracks to use for mapping on
>> OSM? Doesn't compass and altitude data come from GPS satellites anyway?
>> Or an internal altimeter and compass are more accurate?
>>
>> If anybody here has either of the above GPS units and uses them for
>> mapping, it would be useful to hear a first hand opinion.
>
>

Thank you all for the input. Really useful to hear some real life views.

Sebastian

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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

Bill Ricker
barometric altimeter isn't accurate enough for map making, but it's
FUN when driving or hiking through mountains. or harbor tunnels.

all barometric altimeters must be calibrated to known altitude or
known sealevel pressure frequently for any absolute accuracy.

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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

SomeoneElse
Bill Ricker wrote:
> all barometric altimeters must be calibrated to known altitude or
> known sealevel pressure frequently for any absolute accuracy.
>

... and (at least with my eTrex Vista) the compass needs recalibrating
by turning it around twice after a battery change.

Cheers,
Andy


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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

John F. Eldredge
In reply to this post by Sebastian Arcus
Sebastian Arcus <[hidden email]> wrote:

> I was looking at the eTrex series from Garmin to use for mapping on
> OSM,
> as they seem to be robust, compact and have specially long battery
> life
> (25 hours on 2 AA batteries). The main difference between 20 and 30
> seems to be that 30 has altimeter and compass, while 20 doesn't have
> them. Is this important when recording GPS tracks to use for mapping
> on
> OSM? Doesn't compass and altitude data come from GPS satellites
> anyway?
> Or an internal altimeter and compass are more accurate?
>
> If anybody here has either of the above GPS units and uses them for
> mapping, it would be useful to hear a first hand opinion.
>
> Thanks,
>
> Sebastian
>
> _______________________________________________
> newbies mailing list
> [hidden email]
> http://lists.openstreetmap.org/listinfo/newbies

The altitude reading on civilian-model GPS units is not particularly reliable; the altitude information from the satellites has deliberate random errors built in, to make it difficult for someone to use a civilian GPS to plan an artillery or rocket attack.  The GPS units used by the US military can decode more accurate, but encrypted, altitude data.

--
John F. Eldredge -- [hidden email]
"Reserve your right to think, for even to think wrongly is better than not to think at all." -- Hypatia of Alexandria


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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

Cartinus
In reply to this post by Bill Ricker
The Garmins don't have a pure barometric altimeter. They combine the
height from the GPS measurements with the barometric pressure. They are
"auto calibrated" over a period of twenty minutes.

On 01/31/2013 02:12 PM, Bill Ricker wrote:
> barometric altimeter isn't accurate enough for map making, but it's
> FUN when driving or hiking through mountains. or harbor tunnels.
>
> all barometric altimeters must be calibrated to known altitude or
> known sealevel pressure frequently for any absolute accuracy.


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Cartinus

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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

Steve Bennett-3
On Fri, Feb 1, 2013 at 6:07 AM, Cartinus <[hidden email]> wrote:
> The Garmins don't have a pure barometric altimeter. They combine the
> height from the GPS measurements with the barometric pressure. They are
> "auto calibrated" over a period of twenty minutes.


That's a configurable setting. You can use it as a "pure barometric
altimeter" if you really want.

Personally I have the Oregon 550 and frequently use both the altimeter
and compass (not for mapping though). Both can be disabled if you
really want to save battery life, but even with both on, you typically
get 10 hours from a set of rechargeables.

Steve

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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

Cartinus
On 02/01/2013 03:52 AM, Steve Bennett wrote:
> Personally I have the Oregon 550 and frequently use both the altimeter
> and compass (not for mapping though). Both can be disabled if you
> really want to save battery life, but even with both on, you typically
> get 10 hours from a set of rechargeables.

You can't disable them on the GPSmap 60CSx and you can only disable the
compass on the Oregon 450. The Etrex is a far simpler model, so ...

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Cartinus

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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

Dudley Ibbett
In reply to this post by Steve Bennett-3
When it comes to battery life i think you need to treat Garmin's figures (they are up to) with a degree of caution to avoid disappointment.  For the Oregon they quote 16hrs.  For the 62s 20hrs.  With rechargeables a figure of 60-70% of this is probably more realistic.  Even then you'll probably need to turn the screen brightness down to achieve this.  I always carry spares.

Dudley

Sent from my iPad

On 1 Feb 2013, at 02:54, "Steve Bennett" <[hidden email]> wrote:

> On Fri, Feb 1, 2013 at 6:07 AM, Cartinus <[hidden email]> wrote:
>> The Garmins don't have a pure barometric altimeter. They combine the
>> height from the GPS measurements with the barometric pressure. They are
>> "auto calibrated" over a period of twenty minutes.
>
>
> That's a configurable setting. You can use it as a "pure barometric
> altimeter" if you really want.
>
> Personally I have the Oregon 550 and frequently use both the altimeter
> and compass (not for mapping though). Both can be disabled if you
> really want to save battery life, but even with both on, you typically
> get 10 hours from a set of rechargeables.
>
> Steve
>
> _______________________________________________
> newbies mailing list
> [hidden email]
> http://lists.openstreetmap.org/listinfo/newbies

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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

Steve Bennett-3
On Fri, Feb 1, 2013 at 6:28 PM, Dudley Ibbett <[hidden email]> wrote:
> When it comes to battery life i think you need to treat Garmin's figures (they are up to) with a degree of caution to avoid disappointment.  For the Oregon they quote 16hrs.  For the 62s 20hrs.  With rechargeables a figure of 60-70% of this is probably more realistic.  Even then you'll probably need to turn the screen brightness down to achieve this.

IMHO (again with the Oregon), there are only two useful brightness
settings: minimum, and off. In the dark, the minimum is enough. If
there is ambient light, then even maximum doesn't make much difference
so you might as well turn it off.

Probably a bit OT, sorry.

Steve

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Re: Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

Bill Ricker
In reply to this post by Cartinus
On 1/31/13, Cartinus <[hidden email]> wrote:
> The Garmins don't have a pure barometric altimeter. They combine the
> height from the GPS measurements with the barometric pressure. They are
> "auto calibrated" over a period of twenty minutes.

Based on recent experience, I am quite certain that is not true of
older models e.g. 76csx, or if true, auto-calibration is not very
accurate.  The interstate tunnels under Baltimore Harbor should give
me accurate indication of sea-level in-and-out if I started more than
twenty minutes away with good sky view, and it was quite off.


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