 |
 |
 |
 |
|
 |
 |
SAE J2735-Draft-Rev29 [issued: 12-11-08]
-
258 -
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 three types of
regions – circular, polygons 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.
13
ASN.1 Representation:
ValidRegion ::= SEQUENCE {
direction HeadingSlice,
-- field of view over which this applies,
extent Extent OPTIONAL,
-- the spatial distance over which this
-- message applies and should be presented
-- to the driver
area CHOICE {
shapePointSet ShapePointSet,
-- A short road segment
circle Circle
-- A point and radius
}
}
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[RS39]8181[CH40] 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.
14
ASN.1 Representation:
Circle ::= SEQUENCE {
center Position3D,
raduis CHOICE {
raduisSteps INTEGER (0..32767),
-- in unsigned values where
-- the LSB is in units of 2.5 cm
miles INTEGER (1..2000),
13
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.
14
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.