[PROJ] Altitude

[Greg Troxel]

Javier Jimenez Shaw <j1 at jimenezshaw.com> writes:

> Thanks Greg. I didn't want to frighten Roger at the first chance ;)
>
> When you say "In the US, RTK is usually in NAD83", is it NAD83(2011)? Is
> there any base station using a different (older) reference?

Many US states operate an RTN.  While I haven't dug into all of them,
every one I have looked at specifies "NAD83(2011) epoch 2010.0" and that
is more or less universal as the right answer (for CONUS, and CA is
complicated) mirroring the NSRS.  The differences from older NAD83 to
NAD83(2011) are generally small, and my sense is that anything older is
now regarded as obsolete.   (There is a still a lot of labeling data,
particularly non-geodetic-surveying-accuracy data, as just NAD83.)

> Connected to this... is there any information in the NTRIP protocol that
> tell you the coordinate reference system used? I was not able to find that.
> It would be very useful if I am using the same device in Europe, USA, or
> wherever, that the RTK correction protocol tells me the coordinate
> reference system used for the outputs.

My understanding is that NTRIP is basically a way to connect using
something that feels like http and ask for a named stream
("mountpoint"), and that all of the real information is contained within
that stream, usually RTCM2 for pseudorange differential, and RTCM3 for
carrier phase.  I am not aware of any datum tags, although I think there
are reference station coordinates.

So I think that means one should configure a pair of

  NTRIP address/mountpoint
  datum

for doing RTK.

Agreed it would be nice if this were included.  I'll see if I can figure
anything out.
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