[PROJ] OGC blog post summarising Web-mapping misalignment problem

[Joaquim Luis]

Hello, with the risk of going a bit off topic I have another question about the different WGS84, which is: why are they different?

They all use the same ellipsoid, right? So the difference is in the origin of the referencing system? And if yes, why does it change in the several WGS84 realizations?

Thanks

J Luis

Sent from my iDedo

No dia 22/08/2019, às 14:01, Nick Mein <nick_mein at trimble.com> escreveu:

> Hi Roger,
> 
> The answer is ... it depends.
> 
> If you are using autonomous positions then the positions will be in the reference frame of the satellite orbits. Currently WGS84(G1762) for GPS. But the precision that you are going to get is a couple of meters at best, so the difference between different realizations of WGS84 is fairly much irrelevant. The epoch may be relevant , if the data is still going to be of interest in a couple of decades time.
> 
> If you are using a correction service, then you will need to check with your service provider to find out the reference frame of the positions that your receiver is giving you. It could be ITRFxxxx, it could be a local reference frame such as GDA2020 or NAD83. (For what it is worth - there are proposals to add reference frame information to NTRIP and/or RTCM, but currently there is no way to tell without checking with your provider.)
> 
> Regards,
> Nick.
> 
>> On Thu, 22 Aug 2019 at 18:30, Roger Oberholtzer <roger.oberholtzer at gmail.com> wrote:
>> On Thu, Aug 22, 2019 at 12:51 AM Cameron Shorter
>> <cameron.shorter at gmail.com> wrote:
>> >
>> > Proj folks,
>> > A bit of an update. A few of us have been refining our thinking and description of the web-mapping misalignment problem. Scott from the OGC has noted the importance of this topic and invited us to raise the topics at the next OGC Technical Committee meeting at Banff (9 Sept). (Getting approval to travel to the event is becoming trickier than we'd expected.)
>> >
>> > The OGC has published a blog post from us summarising the issues:
>> > https://www.opengeospatial.org/blog/3045
>> 
>> I have a question about the WGS84 datum ensemble in regards to GNSS
>> receivers. When providing WGS84 locations, how would I know which
>> WGS84 variant is being supplied? Is the receiver involved in this? Or
>> is it the satellites that control this? Is it enough to know the date
>> of the measurement? Or must one track more to know which WGS84 variant
>> is provided?
>> 
>> 
>> 
>> 
>> 
>> -- 
>> Roger Oberholtzer
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