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The moving object algebra defines some functions that work directly on temporal attributes and therefore do not need this kind of translation described above. An example would be the SpeedFunction from the spatio-temporal feature. It takes a temporal spatial point (tpoint) and creates a tdouble with the speed of the object at each point in time. A direct temporal function implements the interface TemporalFunction. If the temporal function does not return a temporal value itself, but a non-temporal , it also implements the interface RemoveTemporalFunction. An example would be the TrajectoryFunction from the spatio-temporal feature, which gets a tpoint and creates a non-temporal trajectory, i.e., a spatial LineString.
Limitations
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As of now, there is a limitation when combining direct temporal functions and normal functions in one expression. In that case, Odysseus creates an error message and you have to split your expression in multiple consecutive map operators. This is because the temporal feature creates a TemporalRelationalExpression for the whole expression, which then evaluates it in a non-temporal way. Unfortunately, the temporal function needs a temporal value as its input and not a non-temporal value. Splitting the expression in two parts helps here, as the following example shows with Trajectory being a direct temporal function and SpatialLength a normal non-temporal function:
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You can use the map operator with temporal attributes just as if you would use non-temporal attributes only. You can mix temporal and non-temporal attributes. Just be careful with the #Limitations Limitations with direct temporal functions.
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