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Cellular forums Home > Archive > GPS > May 2005 > USB/Serial receivers
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USB/Serial receivers
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| Captain Dondo 2005-05-24, 10:56 pm |
| I'm looking for a receiver (actually two receivers) that can communicate
via USB, RS485, or RS232.
Here's what I need:
differential accuracy to within 3' (1m) - in other words, the units have
to be accurate to within 3' of each other; I really don't care if they
are absolutely accurate. I just need to know the relative position of
the two units.
NMEA compatibility
A somewhat rugged case, something that can stand a fairly harsh
environment - full exposure to sun, sub-freezing temps, and lots of water.
Suitable for outside installation.
What I don't need:
maps, sofware, screens, memory, waypoints, etc.
High speed accuracy. This will be mounted to a piece of equipment that
at best does some 2 m/minute, or 0.03m/sec...
I've looked around, and I can't find anything that doesn't cost an arm
and a leg.
I've thought about using the cheap USB units in some sort of
signal-transparent enclosure, but I can't find one of those either....
Anyone have any suggestions?
Thanks.
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| Stan Gosnell 2005-05-24, 10:56 pm |
| Captain Dondo <yan@NsOeSiPnAeMr.com> wrote in
news:11975gqi6b3bm92
@corp.supernews.com:
quote:
> I'm looking for a receiver (actually two receivers) that can
> communicate via USB, RS485, or RS232.
>
> Here's what I need:
>
> differential accuracy to within 3' (1m) - in other words, the units
> have to be accurate to within 3' of each other; I really don't care if
> they are absolutely accurate. I just need to know the relative
> position of the two units.
Well, a consumer GPS won't give you that accuracy. You need survey-grade
equipment for that. The price is in the multi-thousand dollar range.
GPS, unassisted by some sort of differential signal, simply is not
capable of 3 foot accuracy.
--
Regards,
Stan
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin
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| Captain Dondo 2005-05-24, 10:56 pm |
| Stan Gosnell wrote:
quote:
> Well, a consumer GPS won't give you that accuracy. You need survey-grade
> equipment for that. The price is in the multi-thousand dollar range.
> GPS, unassisted by some sort of differential signal, simply is not
> capable of 3 foot accuracy.
>
OK, please educate me. (No irony intended; I don't know much about this
stuff.)
I thought WAAS was supposed to give sub-meter accuracy to the consumer
market?
And if not, what's the greatest accuracy I can expect with consumer
equipment?
Thanks.
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| Stan Gosnell 2005-05-24, 10:56 pm |
| Captain Dondo <yan@NsOeSiPnAeMr.com> wrote in
news:11977eocr8ae728
@corp.supernews.com:
quote:
> I thought WAAS was supposed to give sub-meter accuracy to the consumer
> market?
No, WAAS was developed by the FAA to give greater *vertical* accuracy to
aircraft, so that they could use GPS to fly precision instrument
approaches. It does, as a side effect, increase horizontal accuracy
somewhat.
quote:
> And if not, what's the greatest accuracy I can expect with consumer
> equipment?
*IF* you can receive one of the WAAS satellites, and that's certainly not
guaranteed, then you can expect accuracy of less than 10 meters. Never
sub-meter. WAAS was, as I said, developed for use by aircraft in flight,
and uses geostationary satellites, which are very low on the horizon in
the US, and not visible in most other areas of the earth. Trees, hills,
buildings, etc will all block those signals, so you may not be able to
use WAAS at all where you are. Perhaps you can, though, but even if you
do get a good WAAS lock, you can only expect ~10 meter accuracy about 95%
of the time.
--
Regards,
Stan
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin
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| Captain Dondo 2005-05-24, 10:56 pm |
| Stan Gosnell wrote:
quote:
>
> *IF* you can receive one of the WAAS satellites, and that's certainly not
> guaranteed, then you can expect accuracy of less than 10 meters. Never
> sub-meter. WAAS was, as I said, developed for use by aircraft in flight,
> and uses geostationary satellites, which are very low on the horizon in
> the US, and not visible in most other areas of the earth. Trees, hills,
> buildings, etc will all block those signals, so you may not be able to
> use WAAS at all where you are. Perhaps you can, though, but even if you
> do get a good WAAS lock, you can only expect ~10 meter accuracy about 95%
> of the time.
>
Thanks. Now for a couple more questions on accuracy:
What exactly does the 10m number represent? Is that the maximum
distance from the absolute point that I might get? Or is it the maximum
variation I might expect? In geometric terms, are we talking a diameter
or radius about the "correct" point?
Also, is the accuracy typically repeatable or is the variability random?
In other words, if I am off by, lets say, 5m on the first reading, can
I expect the next reading to be off by the same amount in the same
direction or will the reports vary randomly within the accuracy "circle"?
I guess what I am trying to figure out is if the typical results are
random about the absolute point, then I can make some guesses as to the
correct location, and write a suitable algorithm to deal with it. If on
the other hand, they drift about, then I am probably hosed....
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| Pieter Litchfield 2005-05-24, 10:56 pm |
| My Magellan Explorist with 14 parallel channels and WAAS is about as good as
it currently gets for retail GPS, and it is described as:
"W/WAAS <3 meters, 95% 2D RMS"
I think this translates to "using WAAS you will experience a horizontal
error of less than 3 meters root mean square 95% of the time." The other 5
% is a error greater than or equal to 3 meters.
Expect significanlty worse results if WAAS is unavailable.
"Captain Dondo" <yan@NsOeSiPnAeMr.com> wrote in message
news:11979nu7p6j7555
@corp.supernews.com...
quote:
> Stan Gosnell wrote:
>
>
> Thanks. Now for a couple more questions on accuracy:
>
> What exactly does the 10m number represent? Is that the maximum distance
> from the absolute point that I might get? Or is it the maximum variation
> I might expect? In geometric terms, are we talking a diameter or radius
> about the "correct" point?
>
> Also, is the accuracy typically repeatable or is the variability random?
> In other words, if I am off by, lets say, 5m on the first reading, can I
> expect the next reading to be off by the same amount in the same direction
> or will the reports vary randomly within the accuracy "circle"?
>
> I guess what I am trying to figure out is if the typical results are
> random about the absolute point, then I can make some guesses as to the
> correct location, and write a suitable algorithm to deal with it. If on
> the other hand, they drift about, then I am probably hosed....
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| nobody@nospam.co.uk 2005-05-24, 10:56 pm |
| On Tue, 24 May 2005 15:13:17 -0700, Captain Dondo
<yan@NsOeSiPnAeMr.com> wrote:
quote:
>Stan Gosnell wrote:
>
>
>Thanks. Now for a couple more questions on accuracy:
>
>What exactly does the 10m number represent? Is that the maximum
>distance from the absolute point that I might get? Or is it the maximum
>variation I might expect? In geometric terms, are we talking a diameter
>or radius about the "correct" point?
>
>Also, is the accuracy typically repeatable or is the variability random?
> In other words, if I am off by, lets say, 5m on the first reading, can
>I expect the next reading to be off by the same amount in the same
>direction or will the reports vary randomly within the accuracy "circle"?
>
>I guess what I am trying to figure out is if the typical results are
>random about the absolute point, then I can make some guesses as to the
>correct location, and write a suitable algorithm to deal with it. If on
>the other hand, they drift about, then I am probably hosed....
Stan,
the reading on accuracy will always fluctuate and it will never be the
same all the time so there is no chance of you writing a program to
deal with it , if you look at your gps unit and the "info page" where
it shows the positions of the satellites you will see that the
accuracy is never 100% stable and will vary by a few feet every
second. As the man said before, you need to spend thousands of $$s on
survey equipment to get the accuracy you require
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| You may find this page interesting.
<http://users.erols.com/dlwilson/gps.htm> It's a bit heavy going in
places, but if you (like me) are not into wading through the more
technical parts, you can still get some good information from the
graphs and less technical parts. Hope you find this of value.
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| Dennis Pogson 2005-05-25, 9:55 am |
| Roy wrote:
quote:
> You may find this page interesting.
> <http://users.erols.com/dlwilson/gps.htm> It's a bit heavy going in
> places, but if you (like me) are not into wading through the more
> technical parts, you can still get some good information from the
> graphs and less technical parts. Hope you find this of value.
Since no map/chart can be written/printed to that degree of accuracy, then
is the excercise not rather academic? Or is the data to be used for some
other purpose?
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| David Lee 2005-05-25, 9:55 am |
| Dennis Pogson wrote...
quote:
> <http://users.erols.com/dlwilson/gps.htm> It's a bit heavy going in
>
> Since no map/chart can be written/printed to that degree of accuracy, then
> is the excercise not rather academic? Or is the data to be used for some
> other purpose?
Nonesense! You can prepare a map to any degree of accuracy that you
require. Many conservation surveyors are now using GPS for species
recording and it is critically important to understand the magnitude of the
errors in order to interpret the resulting distribution maps.
David
| |
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| Dennis Pogson wrote:
quote:
> Roy wrote:
>
> Since no map/chart can be written/printed to that degree of accuracy, then
> is the excercise not rather academic? Or is the data to be used for some
> other purpose?
There are a number of uses of GPS receivers that don't involve the use
of maps or charts. Returning to a waypoint that was previously
recorded with the receiver is one. I personally don't worry about
accuracy to this degree, since I know it's good enough for my purposes,
and not good enough to substitute for a land survey. That's all I
really need to know. I think a lot of people are still trying to
figure out the limitations on what they can do with their receivers,
and for that, information on accuracy may be helpful. Other people are
just plain curious. The OP was asking about the accuracy of consumer
GPS units, and the link I posted is a pretty good source for that.
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| Captain Dondo 2005-05-25, 4:55 pm |
| Roy wrote:
quote:
> You may find this page interesting.
> <http://users.erols.com/dlwilson/gps.htm> It's a bit heavy going in
> places, but if you (like me) are not into wading through the more
> technical parts, you can still get some good information from the
> graphs and less technical parts. Hope you find this of value.
>
Thanks, perfect.
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