ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS", Bangkok, May 23-25, 2001
338
The Speed of moving object in period [t ¡_i, tj] is defined as
the distance of observation geometries of moving object at
two instant divided by the length of time period.
Speed(t j_i, tj)=Distance(Oj, O ¡_-|) / ( t ¡_i* tj)The
Direction of moving object at two instant is defined as the
difference of two center vectors of observation geometries.
Direction (t m , t p ) =Center(0 - Center(O m f
Affected Range of moving object is defined as the total
coverage of the moving object in it’s lifetime. That is the
union of observation geometries at all instant.
Range (t 0 , t n ) =Uie{0,1,...,n } Oj
4. 2 Query
We can build spatial temporal query of area moving object
using OPH model.
Example 4: find an area object A which continuously settle
over area B and the length of settled time great timelength:
select A from MO
where (A. Pi inside B
or A. Pi overlap B
or A.Pi equal B
and c-ti> timelength)
or (A.Hi. j inside or overlap or equal B
and t r ti> timelength )
4. 3 Trigger
We can identify the moving area objects which satisfy an
given condition using spatial temporal topological relation
and operations. We define the interaction relation of area
objects as trigger.
Example 5: define an trigger report on moving object A to
illustrate that all object B occurred during period of A,
occurred in area A, and their speed and direction are equal
to A:
Define trigger eventreport
ON A
where B during A and inside A
and B.speed= A.speed
and B.direction=A. direction
DO report B is triggered by A.
Example 6: a moving rainfall strip A, define a trigger on A to
report the area which has time of rainfall exceeding tlength
Define trigger action
On A
From A.P(Geometry, tj,c)
Where c -t, >tlength
Do Report area of A.P
5. Conclusion
The OPH model of area moving object has defined the
observation geometry based spatial distribution of moving
object with change over time, used intersection, union, and
difference of geometry point set to calculate P and H. The
model includes spatial distribution and time evolvement of
moving object, reflects the spatial temporal information
about the generation, evolving, and disappearing of moving
object. We defined the significative spatial temporal
topological relation, and the spatial temporal operation,
query, trigger.
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