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Re: Questions/remarks on pathfinder [message #2220 is a reply to message #2219] Wed, 29 February 2012 08:20 Go to previous message
Messages: 41
Registered: March 2009
Dear Gerald,

the main author of pathfinder is Isa Heinze; I'm not sure if she is already registered here. This week she's away on a conference, so I'll try to answer your questions.

1) As it is done now, pathfinder can't really find straight lines that are parallel to the z-axis.

Yes, right. There is no reason for this in terms of the technique. But pathfinder has a tracking device in mind, in first order a TPC. The actual finding is done in two steps. The first finds a projection of a track in the plane perpendicular to z. And a track parallel to z simply doesn't exist in this projection, since it's only a point.

I can't think of a simple solution from the top of my head -- the track parameters will simply be wrong if you start to change the coordinate system. But you can find the straight lines nevertheless; since each track has its own collection of hits attached to it.

But I'm not sure how you want to use pathfinder -- as track finder or as track fitter?

2) I've observed that sometimes, the result of pathfinder depends on the way the input vector of basicHit is sorted.

Hmm, this shouldn't be. Only one possibility comes to my mind; related to the technical implementation -- if there a two "equivalent" track candidates, always the first one will be chosen. (I could go into greater detail if wanted.) Which one the first is depends on the ordering of the input hits.
In principle the method is global, in the sense that every hit is taken into account with the same weight and at the same time. The choice of finder parameters shouldn't affect this.


When you have eliminated the impossible, whatever remains, however improbable, must be the truth. (Sir A.C. Doyle in Sign of Four)
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