[Qgis-user] Wishing for accurate latitude/longitude from my phone

[Iain at jcis.net.au]

I think this is a great discussion. I have been working with GPS's for well
over 10 years and I have a modest paper with an image showing GPS tracks
from my phone (Galaxy Note), a Garmin Montana and my Trimble Geo7X that
shows these issues with accuracy. I happy to share if someone can explain
how to do so.

I was thinking, Nicolas Cadieux, that I would trust an old crusty surveyor
with a Theodolite and a good set of base stations more than my phone because
surveyors are taught ways of avoiding errors and distributing uncertainties
that others such as myself don't know. All survey is done with parameters of
accuracy and surveyors are trained in understanding this more than
non-surveyors such as archaeologists for example. An experienced surveyor
knows all the techniques.

That being said, surveyors readily embraced the new positioning technology
from the 1960s onwards and the reason we have so many new datums and
projections is that the new surveying technology has allowed the geoid to be
modified so it more correctly models the actual shape of the earth.

Having just gone into the matter of purchasing the best surveying equipment
for archaeological projects my experience is that we had issues with cm
accurate GPS in urban areas due to the canyon effect of signals bouncing off
the infrastructure which indicated using a Total Station in urban areas but
out of the city (rural Australia) we have issues with finding control points
to tie a Total Station into which indicated that using a cm accurate GPS
would be better. In areas around the fringe of Sydney there are steeps
gullies and forest canopy so a compo of GPS to set control points and Total
station was indicated. The GPS would locate control points on the geiod and
the Total station would located itself by resection from the control points
and then could record our locations.

The cost of a GPS + Total Station solution was c$A100000 when you add
subscriptions for software, access to base stations for real time
corrections, annual maintenance, and staff training. This is a huge cost for
a smallish business or project. There seemed to be no alternative to being
locked into a particular manufacturer's ecosystem - Leica, Topcon, Trimble
.etc. Ultimately we did not proceed with the purchase.

The other option is the Trimble Catalyst model where you BYOD and purchase
from Trimble the aerial and software access - this varies in accuracy and
time of availability so you can purchase as much or as little accuracy and
time using the software as you need. So long as you have the money.

I should also point out that your GPS should be able to read and process
more than just GPS and GLONAS satellites. The Japanese Quasi-Zenith
Satellite System for example is optimised for the steep terrain and urban
canyoning typical of Japan. There is also the Galileo navigation system,
funded by the long suffering European tax payer and the Chinese Beidou/
Compass system. I can see these satellites on my GPS and on my phone, but it
is not clear to what extent the units actually read the data and process it
rather than simply tell me it is there. 

Also the physical configuration of the phone adds an error in that you need
to know where the aerial is located and place it on the point to be measured
rather than simply wave it around. 

My sense is that the technology is progressing at a slow pace largely due to
lack of consumer demand. I thought cameras would all have inbuilt GPS in
them by now but only the "extreme" models do. Multi-Global Navigation
Satellite System chips are slowly being deployed but they are not a big
consumer item. Clearly more people but a phone for its camera rather than
its accurate GPS. 

I conclude that we have to live with inaccuracy or pay thousands of dollars
to reduce the inaccuracy to 1-2cm. It seems to me that so long as the
inaccuracy is known and accounted for, this is not so much of a problem. It
is better that we are aware of inaccuracies and lack of precision than
assume that our phone GPS's are precise tools.

As with all technology though, watch this space. 

Cheers

 

Dr Iain Stuart

JCIS Consultants 

P.O. Box 2397

Burwood North

NSW, 2134

 

(02) 9701 0191
(0413) 380116 (m)

 

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