[talk-au] Talk-au Digest, Vol 109, Issue 22

[Warin]

On 7/31/2016 5:58 AM, Nyall Dawson wrote:
>
> On 30 Jul 2016 10:34 PM, "Timothy Ney" <neyfamily1 at gmail.com 
> <mailto:neyfamily1 at gmail.com>> wrote:
> >
> > I am a professional surveyor with knowledge of the changing 
> coordinates. What you are referring to is the adoption of MGA2020. To 
> be implemented 1 January 2017. As mentioned below the new system we 
> consider plate drift, at approximately 7cm per year. The most 
> important element is that the new system will be earth centred using 
> the ITRF whereas AMG66, AMG84 and GDA94 were plate centred. On 1 
> January 2017, all physical marks will be given a new set of 
> coordinates, up to about 1.6m different to GDA94. For a while, two 
> systems will run similtanously, the new plate and earth centred 
> systems. Eventually, the plate centred coordinates will be phased out. 
> It is expected that an adjustment will be conducted each year, and 
> coordinates updated.
>
> I'm struggling to find any information about software support of 
> GDA2020. The icsm FAQ has no mention of this, and I can't find 
> anything relevant re GDA2020 and the widely used open source libraries 
> like proj4 and GDAL.
>
> Can anyone help illuminate?
>
> Nyall
>

There are 3 problems/questions...
_
__Data Storage Datum_
At present OSM uses WGS84. Will that change? In the short term probably 
not. This keeps it 'simple'.

_Data Entry - Datum_
Again OSM tries to use WGS84. If that changes then translation between 
datums will be required, if one or both datums are earth centric then 
the date of the measurement will be required for the translation.

_Data use - Datum_
If the output datum is different from the stored data of OSM again 
translation will be required.

If the output datum is earth centric then the date of the applied 
correction should be stated on the output map (as well as the datum used).
Prediction;
Paper maps produced using an earth centric datum will use a date some 
time in the future, about halfway along the predicted usable life time 
of the map.
'Computerised' maps may adjust their output for the current date... or 
use a fixed date just like the paper map above.

In any short term these maps will not produce any sizable error. Most 
maps are updated from time to time .. so the positional errors will 
probably be acceptable to the general population during the lifetime of 
the map/s.

_Software_
Commercial proprietary software will probably not be publicised other 
than its capability to use earth centric datums. There will need to be 
an accepted storage format that incorporated the data of the measurement 
as well as the datum, that may come out publicly as a 'standard'.
Free ware software will lag behind as usuall.

> >
> > Given that most modern GPS systems in phones, cars etc can only 
> achieve accuraries of 1-3 metres, it will be quite some time before 
> old data will no longer align with the GPS. It should also be noted 
> that most systems including Google use the ITRF, or some reference to it.
> >
> > In summary, the impact to most internet mapping systems will be 
> minimal. Even for surveyors, who is the coordinate information, the 
> update will have minimal impact, as we tend to work in small areas, 
> where coordinates are relative only. The big players are those doing 
> broad scale mapping and other regional wide work. See here for more 
> information.
> >
> > www.icsm.gov.au/gda2020/faqs-2.html 
> <http://www.icsm.gov.au/gda2020/faqs-2.html>
> >
> >
> >
> > On Sat, 30 Jul 2016 at 10:03 PM, <talk-au-request at openstreetmap.org 
> <mailto:talk-au-request at openstreetmap.org>> wrote:
> >>
> >> Send Talk-au mailing list submissions to
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> >>
> >> When replying, please edit your Subject line so it is more specific
> >> than "Re: Contents of Talk-au digest..."
> >>
> >>
> >> Today's Topics:
> >>
> >>    1. Australia "changing coordinates" (Andy Mabbett)
> >>    2. Re: Australia "changing coordinates" (Warin)
> >>    3. Re: Australia "changing coordinates" (Andrew Harvey)
> >>    4. Re: Australia "changing coordinates" (Warin)
> >>
> >>
> >> ----------------------------------------------------------------------
> >>
> >> Message: 1
> >> Date: Fri, 29 Jul 2016 13:40:45 +0100
> >> From: Andy Mabbett <andy at pigsonthewing.org.uk 
> <mailto:andy at pigsonthewing.org.uk>>
> >> To: talk-au at openstreetmap.org <mailto:talk-au at openstreetmap.org>
> >> Subject: [talk-au] Australia "changing coordinates"
> >> Message-ID:
> >>         
> <CABiXOE=95mWdWn1P4SvG3ekrRktk0PEvhGNqZ=c2vgxrbHHEcA at mail.gmail.com 
> <mailto:c2vgxrbHHEcA at mail.gmail.com>>
> >> Content-Type: text/plain; charset=UTF-8
> >>
> >> See you when you reach England ;-)
> >>
> >> http://www.bbc.co.uk/news/technology-36912700
> >>
> >> But seriously: what impact might this have, on OSM?
> >>
> >> --
> >> Andy Mabbett
> >> @pigsonthewing
> >> http://pigsonthewing.org.uk
> >>
> >>
> >>
> >> ------------------------------
> >>
> >> Message: 2
> >> Date: Sat, 30 Jul 2016 08:40:41 +1000
> >> From: Warin <61sundowner at gmail.com <mailto:61sundowner at gmail.com>>
> >> To: talk-au at openstreetmap.org <mailto:talk-au at openstreetmap.org>
> >> Subject: Re: [talk-au] Australia "changing coordinates"
> >> Message-ID: <0485644d-097a-3de6-5bd2-71d49c034f60 at gmail.com 
> <mailto:0485644d-097a-3de6-5bd2-71d49c034f60 at gmail.com>>
> >> Content-Type: text/plain; charset=utf-8; format=flowed
> >>
> >> On 7/29/2016 10:40 PM, Andy Mabbett wrote:
> >> > See you when you reach England ;-)
> >> >
> >> > http://www.bbc.co.uk/news/technology-36912700
> >> >
> >> > But seriously: what impact might this have, on OSM?
> >> >
> >> Very little!
> >>
> >> The change, distance wise, is upto 1.5 metres, well within commercial
> >> GPS uncertainties.
> >>
> >> The change is to the datum. How this will work out with future global
> >> datums we will have to wait and see.
> >>
> >> In another 30 years there will probably be another change of around 1.5
> >> metres again.
> >>
> >>
> >>
> >>
> >>
> >> ------------------------------
> >>
> >> Message: 3
> >> Date: Sat, 30 Jul 2016 13:57:31 +1000
> >> From: Andrew Harvey <andrew at alantgeo.com.au 
> <mailto:andrew at alantgeo.com.au>>
> >> To: talk-au at openstreetmap.org <mailto:talk-au at openstreetmap.org>
> >> Subject: Re: [talk-au] Australia "changing coordinates"
> >> Message-ID:
> >>         
> <1469851051.2451056.680960441.20F38439 at webmail.messagingengine.com 
> <mailto:1469851051.2451056.680960441.20F38439 at webmail.messagingengine.com>>
> >> Content-Type: text/plain
> >>
> >> On Sat, 30 Jul 2016, at 08:40 AM, Warin wrote:
> >> > The change, distance wise, is upto 1.5 metres, well within commercial
> >> > GPS uncertainties.
> >> >
> >> > The change is to the datum. How this will work out with future global
> >> > datums we will have to wait and see.
> >> >
> >> > In another 30 years there will probably be another change of 
> around 1.5
> >> > metres again.
> >>
> >> As receivers become more accurate and folks start use other ground 
> based
> >> positioning technology that gives millimetre accuracy, then that 
> data in
> >> OSM will over time become more out of sync as the tectonic plate moves
> >> while the coordinate system remains fixed.
> >>
> >> When that happens it would be good to see a future OSM API that lets us
> >> upload data in a coordinate system like GDA so that we don't need to be
> >> constantly updating coordinates to reflect the move in the techtonic
> >> plate.
> >>
> >>
> >>
> >> ------------------------------
> >>
> >> Message: 4
> >> Date: Sat, 30 Jul 2016 16:22:42 +1000
> >> From: Warin <61sundowner at gmail.com <mailto:61sundowner at gmail.com>>
> >> To: talk-au at openstreetmap.org <mailto:talk-au at openstreetmap.org>
> >> Subject: Re: [talk-au] Australia "changing coordinates"
> >> Message-ID: <5d2da84e-151b-b07c-4e33-57fc7a068eaf at gmail.com 
> <mailto:5d2da84e-151b-b07c-4e33-57fc7a068eaf at gmail.com>>
> >> Content-Type: text/plain; charset=utf-8; format=flowed
> >>
> >> On 7/30/2016 1:57 PM, Andrew Harvey wrote:
> >> > On Sat, 30 Jul 2016, at 08:40 AM, Warin wrote:
> >> >> The change, distance wise, is upto 1.5 metres, well within 
> commercial
> >> >> GPS uncertainties.
> >> >>
> >> >> The change is to the datum. How this will work out with future 
> global
> >> >> datums we will have to wait and see.
> >> >>
> >> >> In another 30 years there will probably be another change of 
> around 1.5
> >> >> metres again.
> >> > As receivers become more accurate and folks start use other 
> ground based
> >> > positioning technology that gives millimetre accuracy, then that 
> data in
> >> > OSM will over time become more out of sync as the tectonic plate 
> moves
> >> > while the coordinate system remains fixed.
> >> >
> >> > When that happens it would be good to see a future OSM API that 
> lets us
> >> > upload data in a coordinate system like GDA so that we don't need 
> to be
> >> > constantly updating coordinates to reflect the move in the techtonic
> >> > plate.
> >>
> >> Sigh.
> >>
> >> Simply changing from AGD66 to GDA94 can produce a change of around 
> 100 metres in location of a coordinate.
> >> So a change in datum can correct the drift without changing the 
> coordinates.
> >>
> >>
> >>  From the above you can see that OZ moves at upto about 50 mm per year.
> >>
> >> At present there is no datum system that 'drifts' over time, that 
> would give a system that would need little alteration and fewer of them.
> >>
> >> People who require the accuracy take into account the drift 
> (usually professional surveyors with very expensive receivers, 
> antennas etc.).
> >>
> >>
>

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