RE: [fluka-discuss]: Minimum distance to nearest boundary

From: Anton Lechner <>
Date: Thu, 13 Jul 2017 09:21:53 +0000

Dear Chris,

I am afraid that an accurate value of the minimum distance to the nearest boundary in a volume is not available - in fact is not strictly needed for the simulation.

For a particle step - in particular for charged particle steps which are small - one often does not need an accurate value, but an approximate value can be sufficient. This approximate value can be smaller than the real minimum distance, but can give an advantage in CPU time as it can be much faster calculated than a more accurate value (which can anyway not always be obtained analytically). This distance is accessible in the variable (DDNEAR) in the common CMMDNR, but depending on the type of body, it might only be a rough estimate (smaller than the real minimum) or it is not calculated at all (in the latter case it is set to zero). If this distance zero or if it is smaller than the step length, then the geometry tracker is used to propagate the particle, but also in this case one does not need the minimum distance but one needs to determine the intersection with a surface in the particle direction (while the minimum distance can theoretically be in the opposite direction).

Cheers, Anton

From: [] on behalf of Andrea Fontana []
Sent: 13 July 2017 10:28
To: Chris Theis; (
Subject: Re: [fluka-discuss]: Minimum distance to nearest boundary

Hi Chris,
    have you tried with PLOTGEOM? Alternatively, there are some interesting
equations at this link (look under "Mathematics/Distance"):

that can perhaps be implemented in an algorithm.
Hope this helps,

Il 12/07/2017 10:24, Chris Theis ha scritto:
> Dear colleagues,
> for some user routines I would need to find the minimum distance from
> a point in a volume to the nearest boundary of this region. As this is
> a standard functionality of a tracker I guess that there should be a
> routine in FLUKA’s geometry package that one could call to obtain this
> information. However, I was not very successful so far in finding it.
> If somebody could give me a hint it would be greatly appreciated.
> Thanks a lot
> Chris

Dr. Andrea Fontana                    tel: +39 0382 987991
Istituto Nazionale                    fax: +39 0382 423241
di Fisica Nucleare
Sezione di Pavia                      e-mail:
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27100 PAVIA, Italy
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Received on Thu Jul 13 2017 - 12:32:06 CEST

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