User's Manual

UtiliNet® Endpoint User Guide 11-1-2006
Page 19 of 30
© Cellnet 2005
in a logical way, it is not necessarily important that the lat/long coordinates be physically accurate. What is
important, is that the lat/long coordinates of each radio be relatively correct to one another.
In other words, if each radio in a particular network was programmed with the same distance offset from
the actual physical location, network routing would not be adversely affected. However, if only a few of the
radios were programmed with the offset, routing could potentially suffer due to logical routing that does not
reflect the physical topology of the network. Therefore, it is not necessary for radios to have exact
coordinates. What is important, however, is that the method used to derive the lat/long coordinates be
capable of providing repeatable coordinate information which is physically relative and consistent system
wide.
Below are the most common, commercially available, methods of deriving latitude longitude information.
A brief analysis has been provided to compare and contrast the benefits of each.
• Global Positioning Systems
• United States Geological Survey Maps
• MapInfo®
Global Positioning System (GPS)
GPS devices receive global positioning information from government owned and operated satellites. Many
manufacturers have developed consumer grade GPS devices for the commercial market. In most
commercial applications, the GPS is used to approximate a location while in motion (such as boating,
hiking, or skiing). These devices are readily available to the consumers for a price of about $500.00 or
less.
As a note, the signal from the government satellites has intentionally
been degraded for security purposes. Commercial grade GPS
specifications are typically +/- 300 meters. Only industrial grade GPS
equipment, with a land based reference, will provide the type of
accuracy used in military applications.
When considering the use of a GPS for constructing and maintaining a UtiliNet network, here are some
issues to evaluate:
Repeatability of the GPS information has proven to be less than ideal. Readings taken from the same
physical location at different times of the day tend to vary significantly (often more than the specified +/-
300 meters). As mentioned earlier, it is most important that the radios’ lat/long coordinates be
RELATIVELY correct to one another. Using a GPS may compromise the repeatability of relatively correct
readings. The user may want to occasionally verify the GPS.
• When using a GPS it is necessary to physically visit each site in order to derive the lat/long coordinates. It
may be desirable to pre-program the radios before they are taken to the site to be installed. This would
require two trips to the site.
• Logistically speaking, only those with the GPS have the ability to derive lat/long coordinates. Efficient
network deployment and maintenance could be compromised or limited by the availability of the GPS.
United States Geological Survey Maps - USGS Maps
USGS maps are readily available from local maps stores, through mail order, and from USGS directly.
Each map section has lat/long coordinates printed along the borders of the map. When considering the use
of a USGS map for constructing and maintaining a UtiliNet network, here are some issues to evaluate:
• Because all USGS maps have a central reference, all derived lat/long coordinates will always be relatively
correct to one another. As mentioned earlier, this is important when considering UtiliNet’s logical routing