[Nfb-science] Hello

[aerospace1028 at hotmail.com]

>Message: 10
>Date: Mon, 12 Jul 2010 10:51:10 -0500
>From: "qubit" <lauraeaves at yahoo.com>
>To: "NFB Science and Engineering Division List"
    ><nfb-science at nfbnet.org>
>Subject: Re: [Nfb-science] Hello
>Message-ID: <DA8454D1F6264DE1AC7135F8D9375D24 at bassclef>
>Content-Type: text/plain;    charset="iso-8859-1"
> 
>no, it is easy to create a 3d tactile picture by simply raising the line 
>that is in front and deleting part of the image underneath.
>In fact, it is an optical illusion when it is done in ink, but with a 
>tactile picture, you are working in 3 dimensions, so you have a truer 
>picture.
>--le

I would like to disagree,

Take, for example, a wire-drawing of a cube in partial profile: the front face would be visible on the page as asquare, and the top and left side faces would be vissible in fore-shorten fassion.  I agree that playing around with the thicknesses of the lines would make it vissually more 3-d.  However if you close your eyes and use your hands, you don't get the sensation of a cube.

If I were to encounter this tactile diagram, I would find the following.

Starting at the right-hand edge, there is a virticle line: call it line A.  At the bottom of line A is a horizontal line attatched to Line A at a ninety-degree angle: call it Line B.  Running left along Line B, I would encounter an intersetction of three lines.  Line C, intercects Libe B at some angle and slants up and to the left.  Line D, conects t Lines B and C at the same juncture and namakes a ninety-degree angle to Line B.  At the End fLine C, another line angles the rest of the way to verticle and runs paralel to Line D: call this Line E.  Line E sticks up higher than Line D, And at its end isanother 3-way interection.  One line--call it Line F-- runs horizontally to the right, while the other line--call it Line G-- slants down to connect to Line D.  Another line--Line H--also runns horizontally to the right out of the intersection between Lines D and G.  Line H runs over an connects back to line A.  A final line--Line I--finishes off the figure running at a slant up and to the left from the top of Line A to the end of Line F.

This figure results in three enclosed spaces.  The space bounded by sides A, B, D, and H forms a square.  However, the spaces bounded by Lines C, D E and g and by F, G H and I both produce a more trapizoodal shape.

The slanted lines to show perspective (Lines C, G an I) produce the opticle illusion of depth.  In an actual cube, all lines would have the same length, all angles between planes will be normal (ninety-degrees).  However, this is *NOT* what is conveyed tactically.  While i t appears vissually that Lines C, G, and I run into and out of the page, when you put your hand on them, they look like slanted lines.  The same sensation of depth is not present.

 		 	   		  
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