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Path: utzoo!watmath!clyde!cbosgd!ihnp4!qantel!hplabs!utah-cs!peterson
From: peterson@utah-cs.UUCP (John W Peterson)
Newsgroups: net.graphics
Subject: Re: ray casting (far too long...)
Message-ID: <3473@utah-cs.UUCP>
Date: Tue, 17-Sep-85 14:24:38 EDT
Article-I.D.: utah-cs.3473
Posted: Tue Sep 17 14:24:38 1985
Date-Received: Thu, 19-Sep-85 07:29:07 EDT
References: <1858@bmcg.UUCP>, <318@gcc-bill.ARPA>
Organization: Univ of Utah CS Dept
Lines: 33

In article <318@gcc-bill.ARPA> brad@gcc-bill (Brad Parker) writes:
>
> "The idea I use to explain this is the so called "pin hole camera"..."
> "...Ps: Your pictures will probably come out upside down the first time..."

Your pictures don't have to come out upside down.  The pinhole camera
method uses a model like:
				        /^
image	|\	/		    |\/  | 
plane->	|  \ +/   --> To image      v/\  |
	|  /  \			        \|
	|/   |  \              So things get turned
             |                 upside down like this.
focal point--+                 

A simpler method is to place the focal point at the eye, so the 
model looks like this:

	   /
         /			       /^
       /+		             /  |
     /  |			   /^   |
eye +   |   ---> To image        /  |   |
     \  |			 \  |   |
       \+			   \|   |
        ^\			     \  |
	|  \			       \|
image---+                        Now things stay
plane				 right side up.

This also has the advantage of making the geometry involved more intuitive.

-jwp


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