[Halld-offline] vertex position from hit-based tracks

[Simon Taylor]

Hi, Craig.

You can get the position of the closest approach to the beam line of the 
track using the position() method; e.g. track->position();

You can track to any plane using one of the methods of the 
DReferenceTrajectory class ( a DReferenceTrajectory object is attached 
to the wire-based track).  Here's a code snippet:

 DReferenceTrajectory *rt=const_cast<DReferenceTrajectory *>(track->rt);
 DCoordinateSystem st_plane;  // plane parameters
  double s; // path length
 double doca=rt->DistToRT(&st_plane,&s);     // Distance of closest 
approach between plane     // and track

Simon

Craig Bookwalter wrote:
> Hi folks,
>     I'm looking for a couple methods to help me determine the event 
> start time, namely:
>     - a method for getting the vertex position of a hit-based track in 
> the CDC or FDC
>     - a method for getting the path length along a hit-based track from, 
> say, the start counter to the target (this would require some 
> association between start counter hits and CDC/FDC tracks, which I'm not 
> sure is happening yet)
>
>     I've looked through the DOxygen docs and haven't seen anything that 
> stuck out to me, but I certainly could have missed something. If these 
> guys do not yet exist I would be happy to help implement them.
>
>     Thanks in advance!
>
> --cb
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