Direction as a spatial object
Shashi Shekhar, Xuan Liu · 1998
Direction is an important spatial relationship that is used in many fields such as geographic information systems(GIS) and image interpretation.It is also frequently used as a selection condition in spatial queries.Previous -work has modeled direction as a relationship predicate between spatial objects.Conversely, in this paper, we model **ion as a new kind of spatial object using the concepts of vec-tOX-S, points ad angle-s.The basic approach is to model direction as a unit vector.Gkwn an ordered pair (P1,P2) of spatial points, one can define a direction, which can take the values of N'orth, Northwest, 3 o'clock, etc. to represent the corresponding qualitative directional predicates on (P1,P2) in previous work.Direction objects can also have quantitative operations such as direction-composition and direction-reverse.This novel tie-w of direction has several obvious advantages First, it allows us to deiine the orientation of spatial object% Second, a richer set of predicates and operators on direction and orientation can be define~Third, new spatial data ~TPessuch as oriented spatial objects and unbounded spatial objects can be defined-Finally, the object view of direction makes it easy to do direction reasoning, which is useful in spatial query processing and optimization-Key-worck Dwection, Orientatio~unbounded object, oriented spatial object.