Glittertinden, a mountain in Norway have a geopos 61.651222 N 8.557492 E,
alternate geopos 6835406.62, 476558.22 (EU89, UTM32).
Some of the mountains are measured to within a millimeter in elevation. For
example Ørneflag is measured to be at 1242.808 meter, with a position
6705530.826, 537607.272 (EU89, UTM32) alternate geopos 6717133.02, 208055.24
(EU89, UTM33). This is on a bolt on the top of the mountain.
There is an on-going project to map the country withing 1x1 meter and
elevation about 0.2 meter.
One arc second is about 1 km, so five digits after decimal point should be
about 1 cm lateral precision.
Goepositions isn't a fixed thing, there can be quite large tidal waves, and
modelling and estimating them is an important research field. The waves can
be as large as ~0.3 meter. (From long ago, ask someone working on this.)
Estimation of where we are is to less than 1 cm, but I have heard better
All geopos hould have a reference datum, without it it is pretty useless
when the precision is high. An easy fix could be to use standard profiles
with easy to recognize names, like "GPS", and limit the precision in that
case to two digits after decimal point on an arc second.
Note that precision in longitude will depend on actual latitude.
On Fri, Sep 1, 2017 at 9:43 PM, Peter F. Patel-Schneider <
The GPS unit on my boat regularly claims an estimated
position error of 4
feet after it has acquired its full complement of satellites. This is a
fairly new mid-price GPS unit using up to nine satellites and WAAS. So my
recreational GPS supposedly obtains fifth-decimal-place accuracy. It was
running under an unobstructed sky, which is common when boating. Careful
use of a good GPS unit should be able to achieve this level of accuracy on
land as well.
the raw accuracy
of the positioning information from a satellite is less than 2.4 feet 95%
the time. The accuracy reported by a GPS unit is degraded by atmospheric
conditions; false signals, e.g., bounces; and the need to determine
by intersecting the raw data from several satellites. Accuracy can be
improved by using more satellites and multiple frequencies and by
comparing to a signal from a receiver at a known location.
The web page above claims that accuracy can be improved to a few
in real time and down to the millimeter level if a device is left in the
same place for a long period of time. I think that these last two
accuracies require a close-by receiver at a known location and correspond
to what is said in .
On 08/30/2017 06:53 PM, Nick Wilson (Quiddity) wrote:
On Tue, Aug 29, 2017 at 2:13 PM, Stas Malyshev
Would four decimals
after the dot be enough? According to  this is what commercial GPS
device can provide. If not, why and which accuracy would be appropriate?
I think that should be 5 decimals for commercial GPS, per that link?
It also suggests that "The sixth decimal place is worth up to 0.11 m:
you can use this for laying out structures in detail, for designing
landscapes, building roads. It should be more than good enough for
tracking movements of glaciers and rivers. This can be achieved by
taking painstaking measures with GPS, such as differentially corrected
Do we hope to store datasets around glacier movement? It seems
possible. (We don't seem to currently
I skimmed a few search results, and found 7 (or 15) decimals given in
one standard, but the details are beyond my understanding:
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