GPS data logging for RINEX file?

I'm looking for suggestions for a GPS that will be used to log the data
required to create a RINEX file, for post-processing to get high
accuracy 3D positions (ideally 0.5m, 95% of the time, but 2m could be
acceptable). I hope to use one of the free online services that
provide precise positioning corrections.

The GPS will be in a light aircraft, so the speed could be up to 250
kt.

The data logging would likely be on a computer running Apple's OS X, so
data logging software that runs on unix type operating systems is
required. I have limited programming experience in Python and Perl,
but would be prepared to learn another language if that was the only
solution.

A remote antenna is a significant plus, but is not strictly required.

Ideally, the GPS, when not being used to log data, could be used as a
WAAS capable handheld GPS.

Cost is a consideration.

I've been Googling for several days, but haven't hit the jackpot yet.
Garmin units seem to have the widest variety of software available. I
would greatly appreciate any suggested GPS units + software. Thanks in
advance for your advice.
--
Kevin Horton
Ottawa, Canada
http://www.kilohotel.com/rv8

How far away are you from the reference station? If you're doing
postprocessing with single frequency receivers, you probably need to be
within 10-20 miles. With dual frequency receivers, you can go much
further.

I'll assume you don't have thousands of $$ for a dual frequency
receiver. You are probably looking at OEM receiver boards. They usually
cost $120-$170, require another $40 in parts, and need a bunch of
soldering. I've played with the Thales AC12 and the Antaris LEA-4T,
and I'll be evaluating a Furuno receiver later this month. They are all
good candidates. You can find external aircraft antennas on e-bay for
another $50 or so.

There is one, really inexpensive solution you might want to look at.
Conrad electronics, a German company, has a USB "hocky puck" receiver
for under $100. It is based on the Antaris LEA-4S. I haven't played
with one yet, but I've heard they have raw measurements and are
"ready-to-go" including an antenna. Unfortunately, Conrad doesn't
import to the US or Canada.

Software wise. the free software is fairly limited. I've been working
on a package off and on to produce Rinex and do "simple" double
differencing. You're welcome to browse through it on my website, but it
definitely needs work. There is also a Garmin package floating around.

How important is .5m accuracy at 250kts? Most receivers provide
updates once per second. Some, like the LEA-4T will do 10 updates a
second. Even at 10hz, you're moving a fair distance between updates.

- John Morris
www.precision-gps.org

I have post-processed (carrier phase) at 100 miles and usually get the
accuracy he wants--but you have to look carefully at the data. The question
is also how long he is willing to sit on the spot.

John wrote:

If I use traditional DGPS with a reference station, I would use the one
at Ottawa, which is about 34 nm from the airport where I would be doing
the performance testing.



The Antaris LEA-4T certainly looks interesting, but I would hope to
find a source for working systems, at least a system on a board that I
could put inside a chassis. I'll keep Googling. Maybe something will
come up on eBay.


I'll try your package out, assuming I acquire a suitable GPS receiver.


The flight path during the periods of interest will be fairly straight,
so I expect to draw a line through the positions and work from there.
I'll be using the GPS data to determine the distance from the start of
the take-off run until the aircraft is 50 ft above the runway, and the
reverse for the landing. I don't "need" any particular accuracy, but
this approach isn't worth the trouble unless I can get about 2m
vertical accuracy, hopefully better. The speed during the times of
interest will be less than 100 kt, but I would hope the system could
work with degraded accuracy up to 250 kt.
--
Kevin Horton

In order to use most of the free services, the RINEX file submitted needs
to have two frequency L1/L2 data. This 'ups' your receiver requirement
quite a lot! As a minimum you will need a L1/L2 capable receiver that
provides carrier phase data suitable for post processing. The 'Gold
Standard' in post processing and user supported software is:

http://facility.unavco.org/software/teqc/teqc.html

Post processing is most accurate when the data is collected at a fixed
point for long periods of time. Collecting data for accurate post processing
from a moving aircraft seems a little futile.

Tom

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