Hello,

I recently climbed ;-) a peak in a south-eastern European country
that was almost 1200 m high. The individual route positions were
determined and also recorded by a Garmin GPSMAP 64s by evaluating GPS
and GLONASS signals; for optimal reception of the satellite signals,
I used the (external) Tallysman TW4421 antenna, which is optimized
for receiving the satellite systems mentioned:
<https://www.farnell.com/datasheets/2860212.pdf>

The antenna in question was in the compartment provided for it in the
baseball cap specially developed by Trimble

<https://www.directupload.eu/file/d/8672/cb3gyk7a_jpg.htm>

which I, as a freak, had of course put on ...

Here is a report on the advantages of using this antenna:

<https://www.navigation-professionell.de/garmin-gpsmap-64-externe-antenne-tallysman/>.

But now finally to my question: After comparing the course of my
tracks in the summit area

<https://www.directupload.eu/file/d/8672/fkikpcbu_jpg.htm> (thin blue
lines, outward and return routes)

I had to realize that "my" route deviates quite significantly from
the OSM route (red dots). I am now wondering whether my track is now
sufficiently accurate to change the OSM route accordingly. After all,
the reception was always optimal thanks to the device configuration,
and the outward and return routes are more or less congruent. What do
you gnss experts think?

Many thanks in advance for your opinions!

Best regards

Reinhard

On 2024-09-16 05:22, Reinhard Zwirner wrote:
> Hello,
>
> I recently climbed ;-) a peak in a south-eastern European country
> that was almost 1200 m high. The individual route positions were
> determined and also recorded by a Garmin GPSMAP 64s by evaluating GPS
> and GLONASS signals; for optimal reception of the satellite signals,
> I used the (external) Tallysman TW4421 antenna, which is optimized
> for receiving the satellite systems mentioned:
> <https://www.farnell.com/datasheets/2860212.pdf>
>
> The antenna in question was in the compartment provided for it in the
> baseball cap specially developed by Trimble
>
> <https://www.directupload.eu/file/d/8672/cb3gyk7a_jpg.htm>
>
> which I, as a freak, had of course put on ...
>
> Here is a report on the advantages of using this antenna:
>
> <https://www.navigation-professionell.de/garmin-gpsmap-64-externe-antenne-tallysman/>.
>
> But now finally to my question: After comparing the course of my
> tracks in the summit area
>
> <https://www.directupload.eu/file/d/8672/fkikpcbu_jpg.htm> (thin blue
> lines, outward and return routes)
>
> I had to realize that "my" route deviates quite significantly from
> the OSM route (red dots). I am now wondering whether my track is now
> sufficiently accurate to change the OSM route accordingly. After all,
> the reception was always optimal thanks to the device configuration,
> and the outward and return routes are more or less congruent. What do
> you gnss experts think?

First off, where you show a 10m error, might be a lesser error depending
on the axis of the error (eg: on a 135°/315° axis).

Second, trees and hills can mask SBAS (WAAS or EGNOS) which can easily
bring errors up to 5 - 10 metres or worse,

Third, depending on satellite constellation, hills, trees, etc. also
mask satellites which:

1- reduces source info, ad
2- forces satellites used to be more overhead than towards the horizon.
Thus the horizontal error grows,

and

4- maybe the trail map shown has errors in it and you (GPS) were closer
to the actual route than shown.

When I take trail measurements I put the antenna inside my toque.

When I change trail positions on a map I usually have 3 or more
recordings of which about half are walking in the opposite direction.

--
"It would be a measureless disaster if Russian barbarism overlaid
the culture and independence of the ancient States of Europe."
Winston Churchill

On Mon, 16th Sep 2024 11:22:50 +0200, Reinhard Zwirner wrote:

[Track recorded with Garmin GPSMAP 64s + external Tallysman TW4421 antenna]
> I had to realize that "my" route deviates quite significantly from
> the OSM route (red dots). I am now wondering whether my track is now
> sufficiently accurate to change the OSM route accordingly. After all,
> the reception was always optimal thanks to the device configuration,
> and the outward and return routes are more or less congruent. What do
> you gnss experts think?

The 64s is a more than 10 year old L1 GPS/GLONASS only *consumer grade*
GNSS receiver. Adding the consumer grade TW4421 L1 antenna may have
increased reception a bit. But considering, that we are currently in
a phase of high sun activity, I'd expect such a device combo (without
correction data) to show deviation from real position of 30 m and more.
Even with low sun activity and more-the-less optimal reception such
a device combo will show frequent position deviations above 5 to 10 m.

Therefore, I wouldn't recommend adjusting the current OSM track. (Which
probably isn't derived just from another GNSS track, anyways. If it
truly is a high mountain trail, it may also show up on DTM raster data
and may be digitized from there.)

Bernd

Bernd Rose schrieb:
> On Mon, 16th Sep 2024 11:22:50 +0200, Reinhard Zwirner wrote:
>
> [Track recorded with Garmin GPSMAP 64s + external Tallysman TW4421 antenna]
>> I had to realize that "my" route deviates quite significantly from
>> the OSM route (red dots). I am now wondering whether my track is now
>> sufficiently accurate to change the OSM route accordingly. After all,
>> the reception was always optimal thanks to the device configuration,
>> and the outward and return routes are more or less congruent. What do
>> you gnss experts think?
>
> The 64s is a more than 10 year old L1 GPS/GLONASS only *consumer grade*
> GNSS receiver. Adding the consumer grade TW4421 L1 antenna may have
> increased reception a bit. But considering, that we are currently in
> a phase of high sun activity, I'd expect such a device combo (without
> correction data) to show deviation from real position of 30 m and more.
> Even with low sun activity and more-the-less optimal reception such
> a device combo will show frequent position deviations above 5 to 10 m.
>
> Therefore, I wouldn't recommend adjusting the current OSM track. (Which
> probably isn't derived just from another GNSS track, anyways. If it
> truly is a high mountain trail, it may also show up on DTM raster data
> and may be digitized from there.)

Hallo Bernd,

many thanks, also to Alan, for your comments which are certainly correct.

I'm just surprised that the GNSS tracks of the outward and return
hikes are almost identical despite the time difference.

Best regards

Reinhard

On 2024-09-18 07:34, Reinhard Zwirner wrote:
> Bernd Rose schrieb:
>> On Mon, 16th Sep 2024 11:22:50 +0200, Reinhard Zwirner wrote:
>>
>> [Track recorded with Garmin GPSMAP 64s + external Tallysman TW4421 antenna]
>>> I had to realize that "my" route deviates quite significantly from
>>> the OSM route (red dots). I am now wondering whether my track is now
>>> sufficiently accurate to change the OSM route accordingly. After all,
>>> the reception was always optimal thanks to the device configuration,
>>> and the outward and return routes are more or less congruent. What do
>>> you gnss experts think?
>>
>> The 64s is a more than 10 year old L1 GPS/GLONASS only *consumer grade*
>> GNSS receiver. Adding the consumer grade TW4421 L1 antenna may have
>> increased reception a bit. But considering, that we are currently in
>> a phase of high sun activity, I'd expect such a device combo (without
>> correction data) to show deviation from real position of 30 m and more.
>> Even with low sun activity and more-the-less optimal reception such
>> a device combo will show frequent position deviations above 5 to 10 m.
>>
>> Therefore, I wouldn't recommend adjusting the current OSM track. (Which
>> probably isn't derived just from another GNSS track, anyways. If it
>> truly is a high mountain trail, it may also show up on DTM raster data
>> and may be digitized from there.)
>
> Hallo Bernd,
>
> many thanks, also to Alan, for your comments which are certainly correct.
>
> I'm just surprised that the GNSS tracks of the outward and return
> hikes are almost identical despite the time difference.

I'd be happy to look at the recorded data, esp. if it has information on
the satellites tracked.

Over any significant distance in the woods and/or steep hills I rarely
get tracks that are "almost identical".

--
"It would be a measureless disaster if Russian barbarism overlaid
the culture and independence of the ancient States of Europe."
Winston Churchill

Alan Browne schrieb:
> On 2024-09-18 07:34, Reinhard Zwirner wrote:
>> Bernd Rose schrieb:
>>> On Mon, 16th Sep 2024 11:22:50 +0200, Reinhard Zwirner wrote:
>>>
>>> [Track recorded with Garmin GPSMAP 64s + external Tallysman TW4421
>>> antenna]
>>>> I had to realize that "my" route deviates quite significantly from
>>>> the OSM route (red dots). I am now wondering whether my track is now
>>>> sufficiently accurate to change the OSM route accordingly. After
>>>> all,
>>>> the reception was always optimal thanks to the device configuration,
>>>> and the outward and return routes are more or less congruent.
>>>> What do
>>>> you gnss experts think?
>>>
>>> The 64s is a more than 10 year old L1 GPS/GLONASS only *consumer
>>> grade*
>>> GNSS receiver. Adding the consumer grade TW4421 L1 antenna may have
>>> increased reception a bit. But considering, that we are currently in
>>> a phase of high sun activity, I'd expect such a device combo (without
>>> correction data) to show deviation from real position of 30 m and
>>> more.
>>> Even with low sun activity and more-the-less optimal reception such
>>> a device combo will show frequent position deviations above 5 to
>>> 10 m.
>>>
>>> Therefore, I wouldn't recommend adjusting the current OSM track.
>>> (Which
>>> probably isn't derived just from another GNSS track, anyways. If it
>>> truly is a high mountain trail, it may also show up on DTM raster
>>> data
>>> and may be digitized from there.)
>>
>> Hallo Bernd,
>>
>> many thanks, also to Alan, for your comments which are certainly
>> correct.
>>
>> I'm just surprised that the GNSS tracks of the outward and return
>> hikes are almost identical despite the time difference.
>
> I'd be happy to look at the recorded data, esp. if it has information
> on the satellites tracked.
>
> Over any significant distance in the woods and/or steep hills I
> rarely get tracks that are "almost identical".

Hi Alan,

I just sent you an e-mail.

Regards

Reinhard

Reinhard Zwirner schrieb:

[...]
> Hi Alan,
>
> I just sent you an e-mail.

.... which bounced immediately :-(

Sighing

Reinhard