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SAE J2735-Draft-Rev28 [issued: 11-10-08]
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279 -
This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
Valid Region
The validity of a sign or advisory can be evaluated spatially using its valid regions. There are two types of
regions – circular, and shape points. Both are described below. Physically being within the area described
by the region is not enough to make a message valid for display. A vehicle must enter the region with the
proper heading. Heading is described by dividing a range of 360 degrees into 16 different segments (each
of which are 22.5° wide) and can be combined to define the required heading of the vehicle when entering
the region.
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ASN.1 Representation:
ValidRegion ::= SEQUENCE { -- Describes geographically bounded region
direction Directions, -- Direction of entry point of region, heading
-- Replace with right DE here, the sliced circle
tag StdTagList, -- Type of region to follow, remove?
area CHOICE {
shapePointSet ShapePointSet -- Vectors describing center, width, and path
-- of valid regions
circle Circle -- Circular region to describe valid area
}
}
Circular Region
A circular region can be used to encompass an entire intersection or a point along a roadway segment. The
region below describes a two-way stop at an intersection. The blue circle describes the entire geographic
area where the sign may be valid. However, the stop sign is only valid when entering from the direction of
Car #1 and Car #2. To constrain the message, we use the direction field (if these directions can be taken as
being east-west then a value of 0x[RS26]8181 would be used). When the vehicle enters a region, the
direction field is checked against the vehicle heading. If it does not match, the sign is not valid. This check
is only performed upon entering the region. Thus, Car #3 will not be presented with the stop sign even if it
turns at the intersection.
A circular region is the simplest region. It works well on small areas like this simple intersection. It can
also be effective for very large areas. A weather advisory for the entire Detroit Metropolitan area can
utilize a large circular region that is valid for all directions of travel.
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DCK thought: Do we need to add a duration and/or distance of validity concept here?
ASN.1 Representation:
Circle ::= SEQUENCE {
center Position3D, -- lat/longitude/elevation of center (J2735)
radius INTEGER (0..999) -- 2 bytes (units of meters)
-- will use map point units, TBD but prob 2.5 CM LSB
-- if you want to cover a region (as for weather alerts)
-- you may need a zoom element here.
}
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DCK Note: This needs a bit more work because your use of “view angle” ( a “vehicles direction while
facing the sign”) seems to also be part of the use/discard determination. Upon further reflection, I am not
sure that element (or the single position one) is really needed, as your region definition seems to handle it
well, and can do the same sign displayed in multiple approaches anyway (such as the same signage on east
and west bound lanes) Unless the actual sign location is needed, can probably drop these elements.
15
This suggests a radius of 100 miles or more, but with less precision on the edge. Perhaps we use a
CHOICE here, either the map element (2.5 cm LSB), or a element with units of “miles” or some such.