4.23. UNIT’S TAIP REFERENCE
e-track
TM
has the ability to detect whether a vehicle is inside or out-
side of a user defined polygon. In order to achieve this the point’s
numeration must follow the next simple rule:
The points must be numerated (starting on 0 and going up to a
maximum of 49) in ascending order according to each point’s
longitude.
If two or more points share the same longitude their index ordering
is not relevant.
If the polygon were drawn with the geographical north pointing up-
wards this rule will be achieved by numerating the points from left
to right.
A point is formed by the
region’s index
, the
point’s index
, the
point’s
latitude and longitude
and by other two parameters called the
left
neighbors
. The
left neighbors
of a point are the indexes of the points
connected (if any) with a line to the actual point and have a longi-
tude value
equal to or less than
the actual point’s longitude. When
the actual point has no left neighbors (there are no connected points
with the same or less longitude) these two parameters take the value
of
99
each, as there is no point with
99
as index
Special cases
•
When the actual point has only one
left neighbor
the first pa-
rameter takes the neighbor’s index and the second must be
99
.
•
When two points lie on the same longitude it is not relevant
which is the point with lower index, but an special considera-
tion must be taken:
When two connected points lie on the same longitude
only one of them, whichever is selected, is left neighbor of the
other.
•
In case that a region has to cross the longitudes
E179.99999
or
W179.99999
or the latitudes
N89.99999
or
S89.99999
the
region must be divided in such a way that it never crosses those
boundaries.
Regions’ creation examples
Take a look to the following regions’ examples that follow the direc-
tions discussed above.
14
A maximum of 50 points may be defined for a single region
137
