Algorithm: Scene graph construction
Input:     A pre-processed video scene (objects are identified,
                  object positions, pointsets and projections
		  are available for each frame)
Output:    A scene graph S(M,R) representing the scene 

begin
 (1)    M = { };   R = { };
 (2)    for each frame F do
 (3)       t = time of frame F relative to start of scene
 (4)       for each object X in F do
 (5)          if X is not already in M then
 (6)             include new object descriptor (X,[]) in M
 (7)          else
 (8)             compute (d,r,I) from current and previous positions
 (9)             append (d,r,I) to track for X
 (10)         endif
 (11)         save current position as previous
 (12)         for each object Y greater than X in F do
 (13)            compute current Rst(X,Y)
 (14)            if there is no edge for (X,Y) in R then
 (15)               include new edge (X,Y,[]) in R
 (16)               save current Rst(X,Y) as existing Rst(X,Y)
 (17)               set time for startOfRst(X,Y) to t
 (18)            else
 (19)               if F is the last frame or
                          current Rst(X,Y) is different to existing Rst(X,Y) then
 (20)                  compute (t,xp,yp,I) based on existing Rst(X,Y)
                          and interval from startOfRst(X,Y) until t
 (21)                  append (t,xp,yp,I) to TS-2D-PIR for edge (X,Y)
 (22)                  save current Rst(X,Y) as existing Rst(X,Y)
 (23)                  set time for startOfRst(X,Y) to t
 (24)               endif
 (25)            endif
 (26)         endfor
 (27)      endfor
 (28)   endfor
end.