POV-Ray : Newsgroups : povray.general : Inverting Normals : Inverting Normals Server Time
11 Aug 2024 07:16:31 EDT (-0400)
  Inverting Normals  
From: Philip Bartol
Date: 21 Aug 1999 03:28:56
Message: <37be5538@news.povray.org>
I recently made a top for my lighthouse out of some CGS stuff, a few torus' 
cutting out a couple of cones merged with a sphere and a cone. I originally 
thought about makeing this in sPatch, but it would have generated a bunch of 
patches and I didn't think I needed to be wasting memory and time on such a 
thing.

I found I could just as easily take a few basic solid shapes and do some math 
on them and make a little CGS object the same way, then I applied a "radial" 
normal to the surface to make it look a little fancier.

The problem came after my first render of the object. I merged all my objects 
together and applied the single normal to the whole object. The problem is the 
cones that I carved out the torus' with had flipped the normal, what POV 
thought I had was the inside of an object (because of cutting it out with a 
torus).

My question that I'm pondering is, is there a way to make sure the whole 
object's outsides really are outside, so to speak. My final solution was to 
make two #declare statements defining normals, one with a positive number on 
the radial and the other with a negative. I applied the one with the neg. 
number to the two objects that had been carved out by the torus and the normal 
with the positive value to the rest of the object. My render was fixed, it 
came out correctly, but this is a goofy way to do it.

I tried all kinds of things to fix this before comming up with this solution, 
doing an intersection with and inverse on the torus.... inverting the final 
difference (which put the camera inside an object)... finally I resorted to 
two normals....

PHIL

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