Re: GPS Accuracy

2000-05-20 Thread Warren Thom 

Hi Allan,

Garmin makes a GPS unit called eMap.  It came out in March 2000.  It sells
for around $200.  Service Merchandise is reducing the line of products they
sell and they have the unit for $150 around here.  These units have the 2.04
version of firmware, but with a PC cable ($30 more) you can upgrade with v
2.5 for "free".  It has a moon and sun "locator" in its 2.5 version of
firmware.  I am not sure what that means - and would appreciate anyone
shedding light on the topic.

Caution:  If you want maps of streets, points of interest, etc. -- you can
only use Garmin Map Source MetroGuide CD ROMs (USA, United Kingdom, France,
Germany, Italy,Sweden and Denmark, or Belgium, Netherlands and Luxembourg  $
124.99 each) with a PC that will load only a portion of the maps onto an
8(`$90) or 16 Meg ($125) cartridge for eMap to use. -- You could connect the
GPS to something like Street Atlas on a laptop (or Palm?) , but that would
defeat the purpose of a hand held mapping device.

I found a lot of interesting things in the last issue of the Compendium.  I
was expecting some discussion on this list about some of the concepts.  It
is a great publication.  I really liked the "interactive" dial of moving
one's hand up a vertical pole - when the hand shadow hit a date line on a
horizontal surface - the hand was on the hour mark.  Any comments - anyone?

Warren Thom
(41.649N  88.096W)

Allan Pratt wrote:

> As most of you know, the US government has relaxed the restrictions on
> the GPS system. Supposedly the accuracy has improved from 10 meters to 1
> meter. My question is, do the actual GPS units in use permit this
> accuracy? At the equator, one degree is 111,308 meters in length.
> One-meter is thus .09 (9 millionths) of a degree. Even as far north
> as Miami FL, a meter is about .1 (1 one-hundred-thousanths) of a
> degree. At my location, a meter is .107 degrees. Do the GPS units
> read out to 5 or 6 decimal digits of accuracy?
>
> Al Pratt
> 33 20 36 N
> 111 54 14

Re: GPS Accuracy

2000-05-13 Thread Richard Langley 

You have been given the wrong information.  Before SA was turned off, the
"official" accuracy was 100 metres (95%) but with 27-28 satellites, typically
accuracy under good conditions was 50-60 metres (95%).  Turning off SA
improved accuracy from 5 to 10 times, so at most to just under 10 metres
(95%) -- but not to 1 metre.  For such accuracies you still need differential
GPS. Most receivers can be programmed to display coordinates in decimal
degrees, degrees and minutes, or degrees, minutes, and seconds.  Grid
coordinates  (northings and eastings are also possible).  There's a wealth of
GPS info on the Web if you need further info.
-- Richard Langley

On Sat, 13 May 2000, Allan Pratt wrote:

>As most of you know, the US government has relaxed the restrictions on
>the GPS system. Supposedly the accuracy has improved from 10 meters to 1
>meter. My question is, do the actual GPS units in use permit this
>accuracy? At the equator, one degree is 111,308 meters in length.
>One-meter is thus .09 (9 millionths) of a degree. Even as far north
>as Miami FL, a meter is about .1 (1 one-hundred-thousanths) of a
>degree. At my location, a meter is .107 degrees. Do the GPS units
>read out to 5 or 6 decimal digits of accuracy?
>
>Al Pratt
>33 20 36 N
>111 54 14
>


=== 
 Richard B. LangleyE-mail: [EMAIL PROTECTED]  
 Geodetic Research Laboratory  Web: http://www.unb.ca/GGE/
 Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142  
 University of New Brunswick   Fax:  +1 506 453-4943  
 Fredericton, N.B., Canada  E3B 5A3
 Fredericton?  Where's that?  See: http://www.city.fredericton.nb.ca/
===