Jonathan, >> Typical producers of this kind of data are numerical particle tracking >> models. These codes step through time, following the (x,y,t) or >> (x,y,z,t) trajectories of individual particles. At each time step, >> more particles may be introduced to be tracked, while other particles >> stop being tracked because they leave the domain, hit the boundary, or >> whatever. > > This kind of data could be described by the trajectory feature type, but each > trajectory would be entirely independent, so they'd all have separate times, > whereas as you describe it the time coord is common to all trajectories (that > exist at a particular time). To arrange this, an indirection could be used on > the time dimension: > data(i,o) x(i,o) y(i,o) z(i,o) t(tindex(i,o)) > where i is the instance (which of the trajectories), o is the point along that > trajectory, t is the coordinate vector of common times, and tindex is an index > to t. For example, we might have these two trajectories (x,t) (omitting y and > z for simplicity) > (0,10) (1,11) (2,12) > (3,11) (2,12) (1,13) (0,14) > Then t would be [10,11,12,13,14] (all the times). For the first trajectory > x=[0,1,2] tindex=[0,1,2] > and for the second > x=[3,2,1,0] tindex=[1,2,3,4] > Is that right? Perhaps/probably there's a neater or more natural way to do it.
Yes, that's exactly right. With the approach you suggest, if you wanted to obtain all the particle positions at a particular time step, would you need to read all tindex for all particles? (I'm a little fuzzy on what the CDL would look like...) Thanks, Rich -- Dr. Richard P. Signell (508) 457-2229 USGS, 384 Woods Hole Rd. Woods Hole, MA 02543-1598 _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
