alice-teacher s Digest, Vol 27, Issue 1

[Funk, Philip]

Hi Don (and Wanda),
	Yes, that does help.  Thanks.
	I will follow your advice and do more investigation of transformation of matrices in 3D graphics.
	Just so I am on the right track, it appears that the "perspective" attribute of the pointOfView is not directly modifiable by the user but it is modified as a result of changing an object's orientation (roll, pitch, yaw) but not by changing an object's position or by changing the camera's position relative to the object.  Am I on the right track?
	BTW, no rush on a response, and no need to post to the forum.  This is not an issue of any importance and probably not one of general interest - just something I would like to understand better.
	Thanks for the help,
		Phil

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Subject: alice-teachers Digest, Vol 27, Issue 1

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Today's Topics:

   1. Re:  Question about Point of View (Don Slater)

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Message: 1
Date: Sun, 30 Sep 2012 09:13:08 -0700
From: Don Slater <dslater at andrew.cmu.edu>
Subject: Re: alice-teacher Question about Point of View
To: Alice educators <alice-teachers at lists.andrew.cmu.edu>
Message-ID: <E9C47834-A6F9-489B-968C-50BE29E59CEA at andrew.cmu.edu>
Content-Type: text/plain; charset="windows-1252"

It is true that their are two explicit components to an object, location and orientation. There is an implicit component as well, distance from camera, that allows a model to be viewed in perspective. As a model is moved closer to, or away from the camera, in a 3D environment, we would expect that object to appear to "grow" or to "shrink". This last value (which is 1 in your example) is used to help with the transformation of the 3D matrix which is used to internally represent the object.

I hope this helps. If you want a more in-depth explanation, look for "transformation of matrices in 3D graphics".

Hope this helps, and my thanks to Wanda Dann in helping me put together this explanation.

Later,
Don Salter

On Sep 30, 2012, at 8:15 AM, "Funk, Philip" <P.Funk at snhu.edu> wrote:

>                 Hi All,
> Each object in an Alice world has a point of view comprised of two components: the object?s position in the world (left right, up down, forward back) and the object?s orientation (yaw, pitch, roll).  In addition, there is a seventh number as shown in the picture below.
>                 <image001.png>
>                 Does anyone know what the last number (1 in this example) means and how it is used?
>                 Thanks,
>                                 P. Funk
> 
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End of alice-teachers Digest, Vol 27, Issue 1
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