Hi Doug:
I recently got a used CSI LGBX Pro DGPS Receiver.
This is a CSI long wave beacon receiver with an integrated Ashtech 12 channel GPS receiver iwth an antenna that receives
both of them.
The display option with the most resolution is dddmm.mmmm and it seems to be
good to less than one foot without averaging.
Note that the LF corrections are coming from an Earth station that's not to far
from where you are receiving them.
The WAAS differential corrections are for a much larger area and may not be as accurate, don't know as so far I don't
have a WAAS corrected GPS.
http://www.prc68.com/I/LGBXcsiDGPS.html
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
Douglas Bateman wrote:
Many thanks to all who, as typical of the list, sent relevant and interesting posts. I would like to comment on some
as follows:
IM: the confluence website - crazy but yet more fun.
RM: the old civil 'degradation' of accuracy of GPS was removed many years ago. Dedicated GPS receivers are more
accurate than smart phones or tablets who use the identity of their routers to give a location, although better than
just a Postcode. See more below.
JT: Google Earth matches the precision in that I found the WGS84 zero line to be exactly where Frank and I were making
our observations. The Google Earth cursor shows incredible precision - down to hundredths of a second of arc.
Centimetre accuracy?
PP: chasing after ephemera (the lat/long lines are moving over long periods, even a year). Never mind, we simply move
our GPS receivers to suit!
FE: the 'confluence dial' in Austria. I remember it as being rather massive and to have moved it would have strained
our party...
TT: GPS averaging apps. Following this I bought two, more below.
KK: HERESY because the WGS84 meridian has nothing to do with the sun. The satellites have large solar panels - just
think of WGS84 as being solar powered!
Spin-off: the dials on the zero meridian UK, France and Spain.
RM: precision with free apps. All very good, and I tried an experiment with my Axxera GPS receiver and two averaging
apps (GPS Averaging and Perfect Mark) on my iPad. The Axxera quotes a CEP of ±2.5 metres, but the experiment was to
see if I could determine a change in longitude by placing a *1 metre rule* aligned with the latitude in a open area on
my lawn. As it happens, for my latitude (51º 22' N) 1 metre corresponds to 0.001 minute of arc in longitude. The
systems update every second so it was no trouble to average 100 samples for 3 sets of readings for each averaging app.
For the GPS Averaging I got 0º 48.1357' and 0º 48.1367' at either end of the rule, and for the Perfect Mark 0º
48.1362' and 0º 48.1377. In other words definitely resolving a metre on the ground. I expect that repeating for
another 600 readings half an hour later (all different satellites and bearings) I may have obtained higher precision
still by combining both sets of data. Amazing.
Thanks again for the fascinating insights. Regards, Doug
PS An image of Frank King and BSS member Ian Butson recording the event of 0º 0' 0". Note the Greenwich landmarks in
the background. The Greenwich meridian passes to the left of the power station chimneys.
On 30/04/2014 17:37, Douglas Bateman wrote:
This is a new club consisting, so far, of two members: Frank King and myself.
After the successful British Sundial Society conference, the Sunday morning was allocated to tours of the Greenwich
Observatory. Quite independently, Frank and I had the intention of location the WGS84 meridian, some 90m east of the
Greenwich brass strip. Frank had an eTrex tracker and an app on his mobile phone, and I had an Axxera GPS tracker
linked to my iPad.
The images, if the system will let them through, show 0º 0' 0". Anyone else willing to join this new exclusive
club? Plenty of places to straddle the line between the north pole and the south pole.
Doug (and Frank)
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