[Phys-L] surveying +- carrier-phase GPS

[John Denker <jsd@av8n.com>]

On 07/29/2018 03:07 PM, bernard cleyet wrote:

> Geologists use(d) an extremely high resolution aneroid barometer.

That's ancient history; see below.

> I had an aviation one with 10 foot labeled dial resolution.  It was 
> spot on (once I’d calibrated w/ the first sign) on my way to skying 
> at Clair Tappan (Sierra Club at Donner pass).

Nowadays for such purposes people use carrier-phase GPS.
In the vertical direction it's much more accurate and
reliable than any barometric altimeter could ever be
... and it gives you horizontal position as well.

  https://www.trimble.com/gps_tutorial/sub_phases.aspx

See also the last two paragraphs of:
  http://uregina.ca/~sauchyn/geog411/global_positioning_systems.html
which links to illustrations:
  http://uregina.ca/~sauchyn/geog411/carrier2.gif
  http://uregina.ca/~sauchyn/geog411/carrier.gif

========

Moving on from surveying, here's another nifty application
of GPS carrier phase:  Put three GPS antennas on an aircraft
(L wingtip, R wingtip, and tail) and look at the differences
in carrier phase.  Quite apart from the GPS position info,
this gives you the *attitude* of the aircraft (i.e. Euler
angles) (i.e. yaw, pitch, and roll) conveniently and accurately.
You have to crunch a few quaternions if you want to convert
from the global dXdYdZ basis to the local NED (north/east/down)
basis, but that's cheap and easy nowadays.