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Re: [lojban] Direction of Rotation

Probably I was misunderstood with my explanations of left/right and line of sight.
Everybody replied that left/right has no relation to clockwise rotation.

In fact the best solution by far (Robin's original right-hand rule)
has this line-of-sight concept innately.

So here is my new picture (attached to the message).
It describes the object N rotating around the axis OT where OT is the vector and your thumb
and OS is another vector visualised as your hand.
N rotates clockwise as marked by the arc AB.

Or, using Robin's definition

N is spinning about axis OT such that if your right hand's fingers are curling in the direction of rotation, your thumb would be pointing in direction T (along the OT axis).
(original Robin's definition is "x1 is spinning about axis x2 such that if your right hand's fingers are curling in the direction of rotation, your thumb would be pointing in direction x3 (along the x2 axis).")

Now we have a problem. Robin's mathematically perfect solution produces lengthy definitions that are not usable (at least in menu items of computer graphic applications).

Let's rearrange those vectors etc. that we have on this picture.

If OS (hand) is perpendicular to OT (thumb) then OS is a useful part of the picture but simply derived from OT.
The point T is beyond the borders of N. It is very important. It allows the observer to look from the point T to OS vector (i.e. the hand in right-hand rule) not being inside the object.
And we get another definition of the same rule.
"x1 rotates moving in the direction of x2 (left/right) which is placed on a plane perpendicular to the axis of rotation that is formed by the center of rotation and the viewpoint x3 (located beyond the bounds of x1) and from which this rotation is observed"
So
"the screen rotates clockwise" = {ti rotro lo pritu mi}
"the screen rotates counterclockwise" = {ti rotro lo zunle mi}
"the screen rotates" = {ti rotro}

By the way using three gismu (proposed earlier) for describing rotation is against the general policy of lojban of having one word for one single phenomenon.

Note that "left/right" is directly derived from Robin's definition. In fact my proposal only rephrases Robin's definition making the resulting translatons to lojban shorter. It changes nothing in the ideology of right-hand rule. No extra assumptions. Still the same picture.
You can't look backwards (as someone noted earlier) and see the object rotating to the left (if it rotates clockwise) because you must look at the hand (OS vector) which is a required part of the scheme.

On Tuesday, August 21, 2012 11:03:40 AM UTC+4, la gleki wrote:
I still have some doubts about "turn to the right/left". It all depends on where your head is. Presumably it's on top of your body and it's looking down to the ground. So {carna} depends on the line-of-sight. Look at this http://farm7.staticflickr.com/6223/6362828499_33a47b6981_z.jpg. It offers you to turn to the right.
Turn the picture 180 degrees. And you'll see something as if you were standing on your head. Now the sign offers you to turn to the left.

So we have to use "line of sight" concept in the definitions anyway. Either in notes to those definitions or in a separate explanatory dictionary of lojban gismu.
On Tuesday, August 21, 2012 4:20:41 AM UTC+4, la .lindar. wrote:
I'm sorry for not digging through this whole thread, but do we have an absolute conclusion?
I could use one of those in the near future. What is the accepted gismu and place structure?

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Attachment: rotro.png
Description: PNG image