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Forum: Geometry
Re: Question Solids whose surface is described by a set of coordinates (Maura E.M.)
Date: 27 Apr, 2016
From: John Apostolakis <John Apostolakis>

Dear Maura,

In my view the most reliable implementation would be to use a “G4Polycone”.

A polycone is a contiguous union of cones which share a common axis.  It include cylindrical sections and surfaces perpendicular to the axis.  

In the simplest implementation you could provide all the points in your specification as “R, Z” pair points of the polycone.  But, depending on the accuracy which you require for the surface, versus the computing performance you require, I suggest to consider reducing the number of conical sections  in which you split your shape.  The computing time for navigating is typically proportional to the number of conical sections.

Best regards,
John Apostolakis
John Apostolakis,  EP Department, CERN

> On 27 Apr 2016, at 02:55, Maura E.M. <> wrote:
> *** Discussion title: Geometry
> Dear GEANT4 geometry experts, I got my first my first modeling
> challenge. I was given the drawings describing accurately a Linac
> Flattening Filter that is usually loosely modelled as a cone sitting on
> a small cylinder. I am requested to model it as from the drawings where
> the external surface profile is defined by an ordered set of (x,y)
> coordinates (plase, see attachment). I can interpolate the given points
> through MatLab and fit a curve. The external FF surface would be
> generated by rotating the plane curve around some straight line (the
> axis) that lies on the same plane. I believe Geant4 allows to build such
> Revolution Solids. I never dealt with that before. I would greatly
> appreciate seeing some examples of similar cases. I feel this is likely
> to regarded as a special component. Thank you so much Best regards,
> Mauede Attachment:
> -------------------------------------------------------------
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