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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