Spatial+Temporal database request for 4D intersection

Question

Here is the function I need to implement. My application deals with mobile objects with variable position and range (think of radar range). As I can't test each minute if n mobiles detect each other (server would be overloaded), I need to precalculate "future" position and time when they'll detect each other from their planned route and only register the "future" event in a stack. Each time a user changes the planned route, I'll recalculate event related to all intersecting routes from other mobiles.

The best way to do that is to make a kind of 4D intersection request and update, and be able to detect when and where mobiles will "collide".

Is it possible with a classic geodatabase like PostgresQL+PostGis and another plugin, or do I need to look at specific n-dimensional database ?

Answer 1

This can be done with PostGIS's ST_LocateBetween function, where you can extract point and linestrings from either a single time or between a range of times. To do this, you need to have geometries with a measure dimension, that is [Multi]Point [Z]M or [Multi]LineString [Z]M geometries. A numeric timestamp (e.g. Unix time) can be used for the M-dimension.

For example, this 4D point is captured at M=4:

SELECT ST_AsText(ST_LocateBetween('POINT ZM (1 2 3 4)'::geometry, 4, 4))
 st_astext
-------------------------
 MULTIPOINT ZM (1 2 3 4)
(1 row)

And if it doesn't intersect the M range, it will return MULTIPOINT ZM EMPTY, which can be filtered out of a query with ST_IsEmpty.

• Zofren: To be more precise on my use case : imagine objects moving along a path. The objects are defined by a MLineString (list of MCoordinate) and an Integer (circle radius). I would like to know when two objects.circle will collide and where each object are when collision occurs. I need to interpolate position and time between two MCoordinate. It seems that in your sample, i'll get only defined points.