[Nfb-science] Hello

[qubit]

well, the way a 3d flat drawing of a cube is done is to put the "visible" 
lines in front as solid lines and the hidden lines behind as dotted lines. 
That is how I remember seeing it visually. Now I confess that I never liked 
the look of the cube diagrams I saw in my old textbooks.  I never got the 
feeling of seeing a 3d object by looking at it, not to mention touching a 
tactile representation of the same cube.  I just came to accept that funny 
shaped drawing as a cube like I accepted a drawing of anything else, like a 
tree or a face.  The 3d effect was nearly lost on me, perhaps due to my 
vision being limited so I didn't see much at a distance.
That being said, one thing that helped me with the perspective drawings was 
to take a graduate course in computer graphics.  (Ok, so it was in the stone 
age in the mid 80s, but the math has not changed.)  We had to develop a 3d 
simple graphics package that could be used to draw any 3d object given only 
a set relevant points.  The midterm was to feed commands through the package 
to draw houses from many perspectives. It was quite interesting, the math 
involved hard crunching of matrices that would map points around as you 
moved.  The obscured lines in the back were represented as dotted lines. 
It's funny, I could barely see what I was drawing, but being a math major, I 
found the course to be quite interesting.  I wonder what an analogous course 
would cover nowadays.
In short, I hated 2d representations of 3d objects even when I could see the 
pictures.  I think that the tactile ones would be easier, for me anyway.
--le

----- Original Message ----- 
From: <aerospace1028 at hotmail.com>
To: <nfb-science at nfbnet.org>
Sent: Tuesday, July 13, 2010 8:38 AM
Subject: Re: [Nfb-science] Hello



>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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