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Tennessee 811 has acquired additional domain
names.
Any domain we presently own will point to the main
site at www.tnonecall.com. Feel free to use any
domain you like in your browser, but just keep in mind
that our emails will still be listed as the main domain
extension.
The new domains are:
www.tn811.com www.tennessee811.com www.tenn811.com |
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Tennessee 811 offers free safety meetings at your
office or work site.
We don't restrict the hours in which to have a
presentation. We work around what works for you! We
can easily have a meeting before your crews go out in
the morning, during lunch or when they arrive back in
the afternoon. We can also tailor the time frame of
the presentation to suit your meeting needs.
Call or email now and ask for Holly Austin or Scott
Holder and we'll be happy to schedule a meeting for
you:
Holly - haustin@tnonecall.com - 615-367-1110 (x7102) Scott - sholder@tnonecall.com - 615-367-1110 (x7140) "Call Before You Dig" is a great safety topic for any
meeting. Even your inside personnel can benefit.
Remember - there is no cost involved to you, and it's a
service we offer. The better educated your employees
are, the safer they will be!
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We thought it might be interesting to run a series about how GPS works. The content for this series comes directly from the Discovery channel's "How Stuff Works" programs via their website. So, sit back and enjoy the read. This article begins the 5th, and final topic in the
series.
Differential GPS So far, we've learned how a GPS receiver calculates
its position on earth based on the information it
receives from four located satellites. This system
works pretty well, but inaccuracies do pop up. For one
thing, this method assumes the radio signals will
make their way through the atmosphere at a
consistent speed (the speed of light). In fact, the
Earth's atmosphere slows the electromagnetic energy
down somewhat, particularly as it goes through the
ionosphere and troposphere. The delay varies
depending on where you are on Earth, which means
it's difficult to accurately factor this into the distance
calculations. Problems can also occur when radio
signals bounce off large objects, such as
skyscrapers, giving a receiver the impression that a
satellite is farther away than it actually is. On top of all
that, satellites sometimes just send out bad almanac
data, misreporting their own position
Differential GPS (DGPS) helps correct these errors.
The basic idea is to gauge GPS inaccuracy at a
stationary receiver station with a known location. Since
the DGPS hardware at the station already knows its
own position, it can easily calculate its receiver's
inaccuracy. The station then broadcasts a radio signal
to all DGPS-equipped receivers in the area, providing
signal correction information for that area. In general,
access to this correction information makes DGPS
receivers much more accurate than ordinary receivers.
The most essential function of a GPS receiver is to
pick up the transmissions of at least four satellites
and combine the information in those transmissions
with information in an electronic almanac, all in order
to figure out the receiver's position on Earth.
Once the receiver makes this calculation, it can tell
you the latitude, longitude and altitude (or some
similar measurement) of its current position. To make
the navigation more user-friendly, most receivers plug
this raw data into map files stored in memory.
You can use maps stored in the receiver's memory,
connect the receiver to a computer that can hold more
detailed maps in its memory, or simply buy a detailed
map of your area and find your way using the
receiver's latitude and longitude readouts. Some
receivers let you download detailed maps into
memory or supply detailed maps with plug-in map
cartridges.
A standard GPS receiver will not only place you on a
map at any particular location, but will also trace your
path across a map as you move. If you leave your
receiver on, it can stay in constant communication with
GPS satellites to see how your location is changing.
With this information and its built-in clock, the receiver
can give you several pieces of valuable information:
We hope you've enjoyed this series. More GIS-type articles will follow in future newsletters. Brain, Marshall, and Tom Harris. "How GPS
Receivers Work." 25 September 2006.
HowStuffWorks.com. Photo courtesy U.S. Department of Defense Artist's concept of the GPS satellite constellation |
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NASCAR No. 29 (Kevin Harvick) featured the 811 logo on the trunk deck of the car during the final race of the season. This event resulted in impressive media placements increasing visibility and public awareness for the 811 campaign. |
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Tennessee 811
email:
tnocs@tnonecall.com
phone:
(615) 367-1110
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