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Reporter: bernard_aboba@… | Owner: martin.thomson@…
Type: defect | Status: closed
Priority: major | Milestone: draft-ietf-geopriv-3825bis
Component: rfc3825bis | Version: 1.0
Severity: Active WG Document | Resolution: fixed
Keywords: |
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Changes (by bernard_aboba@…):
* status: new => closed
* resolution: => fixed
Comment:
I substituted the text in Appendix B.1, leaving B.2 alone. Some of the
original material in Appendix B.1 appeared important in understand the
encoding (such as information on how the Altitude was determined), so I
left that in.
Here is the text of Appendix B and B.1 as it appears in -09:
Appendix B. Calculations of Resolution
The following examples for two different locations demonstrate how
the Resolution values for Latitude, Longitude, and Altitude (used in
the version 0 DHCPv4 option) can be calculated. In both examples,
the geo-location values were derived from maps using the WGS84 map
datum, therefore in these examples, the Datum field would have a
value = 1 (00000001, or 0x01).
B.1. Location Configuration Information of "White House" (Example 1)
The grounds of the White House in Washington D.C. (1600 Pennsylvania
Ave. NW, Washington, DC 20006) can be found between 38.895375 and
38.898653 degrees North and 77.037911 and 77.035116 degrees West. In
this example, we assume that we are standing on the sidewalk on the
north side of the White House, between driveways. Since we are not
inside a structure, we assume an Altitude value of 15 meters,
interpolated from the US Geological survey map, Washington Washington
West quadrangle.
The address was NOT picked for any political reason and can easily be
found on the Internet or mapping software, but was picked as an
easily identifiable location on our planet.
In this example, the requirement of emergency responders in North
America via their NENA Model Legislation [NENA] could be met by a
LatUnc value of 21 and a LongUnc 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.
An approximate representation of this location might be provided using
the version 0 encoding as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code (123) | OptLen (16) | LatUnc | Latitude .
|0 1 1 1 1 0 1 1|0 0 0 1 0 0 0 0|0 1 0 0 1 0|0 0 0 1 0 0 1 1 0 1.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Latitude (cont'd) | LongUnc | .
.1 1 0 0 1 0 1 1 1 0 0 1 1 0 0 0 0 1 1 0 0 0 1 1|0 1 0 0 0 1|1 1.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Longitude (cont'd) |
.0 1 1 0 0 1 0 1 1 1 1 0 1 1 0 1 0 1 0 0 0 0 1 0 1 1 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AType | AltUnc | Altitude .
|0 0 0 1|0 1 0 0 0 1|0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Alt (cont'd) |Ver| Res |Datum|
.0 0 0 0 0 0 0 0|0 0|0 0 0|0 0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In hexadecimal, this is 7B10484D CB986347 65ED42C4 1440000F 0001.
Decoding Location Configuration Information with Resolution
Decoding this option gives a latitude of 38.897647 (to 7 decimal
places) with 18 bits of resolution; a longitude of -77.0366000 with
17 bits of resolution; an altitude type of meters with a value of 15
and 17 bits of resolution; version 0 (resolution) and the WGS84
datum.
For the latitude value, 18 bits of resolution allow for values in the
range from 38.8964844 to 38.8984375. For the longitude value, 17
bits of resolution allow for values in the range from -77.0390625 to
-77.0351563. Having 17 bits of resolution in the altitude allows for
values in the range from 0 to 32 meters.
GML Representation of Decoded Location Configuration Information
The following GML shows the value decoded in the previous example as
a point in a three dimensional CRS:
<gml:Point srsName="urn:ogc:def:crs:EPSG::4979"
xmlns:gml="http://www.opengis.net/gml";>
<gml:pos>38.897647 -77.0366 15</gml:pos>
</gml:Point>
This representation ignores the values included in the resolution
parameters. If resolution values are provided, a rectangular prism
can be used to represent the location.
The following example uses all of the decoded information from the
previous example:
<gs:Prism srsName="urn:ogc:def:crs:EPSG::4979"
xmlns:gs="http://www.opengis.net/pidflo/1.0";
xmlns:gml="http://www.opengis.net/gml";>
<gs:base>
<gml:Polygon>
<gml:exterior>
<gml:LinearRing>
<gml:posList>
38.8964844 -77.0390625 0
38.8964844 -77.0351563 0
38.8984375 -77.0351563 0
38.8984375 -77.0390625 0
38.8964844 -77.0390625 0
</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</gs:base>
<gs:height uom="urn:ogc:def:uom:EPSG::9001">
32
</gs:height>
</gs:Prism>
--
Ticket URL: <http://trac.tools.ietf.org/wg/geopriv/trac/ticket/32#comment:1>
geopriv <http://tools.ietf.org/geopriv/>
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