Possible problem with tracking inside TGeoPgon

There is a possible problem with navigation inside TGeoPgon if the initial position is exactly on the polygon axis.

I have a package which performs tracking of photons using TGeoManager class.
If the starting point is situated exactly on the axis of the polygon, the results are obviously wrong: I see a strong asymmetry in the positions of the ends of the photon “tracks”.
Starting just slightly off the axis (X or Y of 0.0001) cures the problem and I have a perfect symmetry.

The problem does not appear in TGeoTube or TGeoBBox - tracking from the axis performs perfectly well.
Replacing TGeoBBox with a TGeoPgon of exactly the same shape (4 edges, matching rotation) shows the problem again.
The number of edges as well as the position along the axis does not mater - the problem remains.

I do not know will this help or not - the tracking with “on axis” condition in the TGeoPgon is ~40 times slower compared with off-axis conditions.

I am running Root 5.34.36 on Windows

Can you post the parameters of the TGeoPgon you use and starting point/direction?

Best, Andrei

I have tried TGeoPgons with two planes, number of edges from 3 to 50.
The tracing directions were random (isotropic).
Any point on the axis would result in that strange behavior.

Is there anything else I can provide to help with the issue?

Hi Andrei,
Sorry for the delay, I can reproduce and I will provide a fix and let you know.

Best, Andrei

The issue should be now fixed in the master.

Best, Andrei

Thank you Andrei!
Is it fixed in ROOT6 only or ROOT5 too?
We cannot use ROOT6 because it is not available for Windows still.

I have also found a possible tracking problem with TGeoParaboloid.
May I post it here or better create a new forum thread?

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