[Radiance-general] Rendering large space with small detail (small picture now attached!)

[Jack de Valpine]

Hi Rob,
 
[snip]
>> In Autocad (for example) 3dfaces that
>> are built in a clockwise manner will have the normal pointing out of
>> the clockwise face (I hope I am remembering this correctly).
>>     
>
> It's hard to tell from your description if you are or not. Think of it
> this way: let's say you are drawing a polygon that represents the face
> (screen)  of the computer monitor you are now staring at. If you draw the
> points in a clockwise fashion, the surface normal will be pointing away
> from you (out the back of the monitor). If you define it with points in a
> COUNTER-clockwise fashion, the polygon's surface normal will be pointing
> at you. IOW, in the first example, with a glow applied, the monitor face
> would render black. In the latter example, the monitor face would glow.
>
> This can be reinforced by a permutation of the so-called "right hand
> rule". Take your right hand and point at your face with your thumb, and
> then curve your fingers around the axis defined by your thumb; if you
> imagine your fingers pointing in the direction of rotation (and direction
> of point creation), your thumb describes the surface normal (vector).
>
>   

Ack, yes you are absolutely correct! I knew I should have gone and 
actually checked.... Another way to consider this, if you are working in 
the XY plane (Autocad based example here) then counter clockwise gets 
you a normal point in positive Z.

Of course this really applies to surface generated geometry. Solid 
modeling will bring its own set of issues with geometry management....

-Jack

-- 
# Jack de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction

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