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Forum: Geometry
Re: Question Question for G4VSolid::SurfaceNormal() (Yuefeng Qiu)
Re: None Re: Question for G4VSolid::SurfaceNormal() (John Apostolakis)
Re: None Re: Question for G4VSolid::SurfaceNormal() (Yuefeng Qiu)
Re: None Re: Question for G4VSolid::SurfaceNormal() (John Apostolakis)
Date: 08 May, 2014
From: Yuefeng Qiu <Yuefeng Qiu>

Thanks a lot for further suggestions!

Best regards,
Yuefeng
-----Original Message-----
From: John Apostolakis [mailto:John.Apostolakis@cern.ch] 
Sent: Thursday, May 08, 2014 4:32 PM
To: Qiu, Yuefeng (INR)
Cc: <geometry-g4hn@slac.stanford.edu>
Subject: Re: Question for G4VSolid::SurfaceNormal()

Your proposed method is good.  Please see some more detailed comments below.

On May 8, 2014, at 10:41 AM, Yuefeng Qiu wrote:

> If the Point is mostly very near to the surface then it is easy to 
> deal with. I can use a larger Tolerance, for example, 10*kCarTolerence or 100*kCarTolerence to check if on one of the surfaces.

In infrequent cases, you may find larger errors - so I suggest to be a bit more flexible with your definition.   Another factor of ten likely will be adequate for most cases, but if you have large statistics or navigate to surfaces from points which are very far away you may encounter occasional surprises.

> However, if the point is far from the surface, I can return the normal of the nearest surface.
> 
> In my case the surface are analytic surface therefore the normal will 
> be accurate. The only approximation will happen if point are far from the surface.

The answer needs to be correct only for points on the surface.  This fulfills the specification.

If an inquiry is made about points away from the surface, it is fine to return an answer corresponding to the normal at an estimated nearby point.

John

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