On 5/10/12 6:08 AM, Magnus Danielson wrote:
On 05/10/2012 02:50 PM, swingbyte wrote:
Hi all,
Hope this isn't too chat roomy, however, I have need of a survey precise
geolocation type gps. I was wondering if the precise timing abilities
extend to its precision in position output? I have a thunderbolt and one
of those conical white aerials from china and would like to know if this
combination will give me accurate height data.
There are many sides to this issue. You will most definitely be best
served by a choke-ring or similar antenna that suppresses multi-path
reflections. In addition to that, you would want Lady Heather to do a 24
hour position averaging. This should give you an OK solution, but really
not the best achievable.
Accurate height data is complex, since besides the receiver and antenna
issues, height data has more uncertainty than longitude and latitude
measures, and also since even if precise WGS84 height is achieved, you
would need to correct it to your datum, your sea-level etc.
You would also like to have better ionspheric correction than a plain
GPS solution gives you, but the Thunderbolt does not give you direct
support for such corrections.
Exactly how much effort you need to do depends on how accurate you need
it, +/- 10 m, 1 m, 1 dm, 1 cm or 1 mm.
If you can get RINEX format files, you can post process them through
GIPSY at JPL and get higher precision, using post determined ionospheric
and other corrections.
My friends in the GPS world say that getting to 1 meter absolute
position is fairly straightforward but once you start getting finer than
that, all the various factors start ganging up on you: ionosphere, solid
earth tides, multipath, phase center shifts, etc.etc.
Likewise, getting 1mm + 1 ppm of separation distance sorts of
uncertainty in a differential measurement is fairly straightforward.
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