Possible problem with tracking inside TGeoPgon

ROOT
1

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

2

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

Best, Andrei

3

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.

4

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

5

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

Best, Andrei

6

Hi,
The issue should be now fixed in the master.

Best, Andrei

7

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?
Regards,
Andrey

8

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