degrees longitude. This is an area of approximately 339 square
centimeters (20.9cm x 16.23cm).
If: LaRes is expressed as value 30 (0x1e or 011110) and LoRes is
expressed as value 30 (0x1e or 011110), then it would describe a
geo-location area that is latitude 38.8986797 north to latitude
38.8986802 and extends from -77.0372300 degrees to -77.0372296
degrees longitude. This is an area of approximately 19.5 square
centimeters (50mm x 39mm).
If: LaRes is expressed as value 34 (0x22 or 100010) and LoRes is
expressed as value 34 (0x22 or 100010), then it would describe a
geo-location area that is latitude 38.8986800 north to latitude
38.8986802 and extends from -77.0372300 degrees to -77.0372296
degrees longitude. This is an area of approximately 7.5 square
millimeters (3.11mm x 2.42mm).
In the (White House) example, the requirement of emergency responders
in North America via their NENA Model Legislation [8] could be met by
a LaRes value of 21 and a LoRes value of 20. This would yield a
geo-location that is latitude 38.8984375 north to latitude 38.8988616
north and longitude -77.0371094 to longitude -77.0375977. This is an
area of approximately 89 feet by 75 feet or 6669 square feet, which
is very close to the 7000 square feet requested by NENA. In this
example, a service provider could enforce that a device send a
Location Configuration Information with this minimum amount of
resolution for this particular location when calling emergency
services.
A.2. Location Configuration Information of "Sears Tower" (Example 2)
Postal Address:
Sears Tower
103rd Floor
233 S. Wacker Dr.
Chicago, IL 60606
Viewing the Chicago area from the Observation Deck of the Sears
Tower.
Latitude 41.87884 degrees North (or +41.87884 degrees)
Using 2s complement, 34 bit fixed point, 25 bit fraction
Latitude = 0x053c1f751,
Latitude = 0001010011110000011111011101010001
Longitude 87.63602 degrees West (or -87.63602 degrees)
Using 2s complement, 34 bit fixed point, 25 bit fraction
Longitude = 0xf50ba5b97,
Longitude = 1101010000101110100101101110010111
Altitude 103
In this example, we are inside a structure, therefore we will assume
an altitude value of 103 to indicate the floor we are on. The
Altitude Type value is 2, indicating floors. The AltRes field would
indicate that all bits in the Altitude field are true, as we want to
accurately represent the floor of the structure where we are located.
AltRes = 30, 0x1e, 011110
AT = 2, 0x02, 000010
Altitude = 103, 0x00006700, 000000000000000110011100000000
For the accuracy of the latitude and longitude, the best information
available to us was supplied by a generic mapping service that shows
a single geo-loc for all of the Sears Tower. Therefore we are going
to show LaRes as value 18 (0x12 or 010010) and LoRes as value 18
(0x12 or 010010). This would be describing a geo-location area that
is latitude 41.8769531 to latitude 41.8789062 and extends from
-87.6367188 degrees to -87.6347657 degrees longitude. This is an
area of approximately 373412 square feet (713.3 ft. x 523.5 ft.).
6. References
6.1. Normative References
[1] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March
1997.
[2] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,
January 2001.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", RFC
3118, June 2001.
[5] European Petroleum Survey Group, http://www.epsg.org/ and
http://www.ihsenergy.com/epsg/geodetic2.html
[6] World Geodetic System 1984 (WGS 84), MIL-STD-2401,
http://www.wgs84.com/
6.2. Informational References
[7] Farrell, C., Schulze, M., Pleitner, S. and D. Baldoni, "DNS
Encoding of Geographical Location", RFC 1712, November 1994.
[8] National Emergency Number Association (NENA) www.nena.org NENA
Technical Information Document on Model Legislation Enhanced 911
for Multi-Line Telephone Systems.
7. Author Information
James M. Polk
Cisco Systems
2200 East President George Bush Turnpike
Richardson, Texas 75082 USA
EMail: jmpolk@cisco.com
John Schnizlein
Cisco Systems
9123 Loughran Road
Fort Washington, MD 20744 USA
EMail: john.schnizlein@cisco.com
Marc Linsner
Cisco Systems
Marco Island, FL 34145 USA
EMail: marc.linsner@cisco.com
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