[OpenSCAD] Newbie rotation confusion.

[Aurum]

Having now subscribed to the mailing list hopefully this will now be posted.
Sorry if it's posted twice.

What I'm trying to do is understand how to get a cube at the origin with
it's corners on the axes.

Firstly, I tried rotating by 45° about x and y with no success.

I then rotated 45° about the X axis with
rotate(45,[1,0,0]){
color("cyan") cube(10,center=true);
}
and looked down the Y axis. What I see is this.
<Loading Image...>

I now realize that I'm not looking at a square anymore but a rectangle with
sides 10 and 14.14 (10 x root 2) and so to align the corners with the Z axis
I need to rotate by atan(1.414) = 54.7°.

I do this with
rotate(45,[1,0,0]){
rotate(54.7,[0,1,0]){
color("cyan") cube(10,center=true);
}
}
and the result is
<Loading Image...>

What am I doing wrong?

Is there a simple way to get a cube at the origin with it's corners on the
axes?

Mike.



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[nop head]

Post by Aurum
Is there a simple way to get a cube at the origin with it's corners on the

axes?

No it is physically impossible.

Post by Aurum
Having now subscribed to the mailing list hopefully this will now be posted.
Sorry if it's posted twice.
What I'm trying to do is understand how to get a cube at the origin with
it's corners on the axes.
Firstly, I tried rotating by 45° about x and y with no success.
I then rotated 45° about the X axis with
rotate(45,[1,0,0]){
color("cyan") cube(10,center=true);
}
and looked down the Y axis. What I see is this.
<http://forum.openscad.org/file/t2335/cube1.png>
I now realize that I'm not looking at a square anymore but a rectangle with
sides 10 and 14.14 (10 x root 2) and so to align the corners with the Z axis
I need to rotate by atan(1.414) = 54.7°.
I do this with
rotate(45,[1,0,0]){
rotate(54.7,[0,1,0]){
color("cyan") cube(10,center=true);
}
}
and the result is
<http://forum.openscad.org/file/t2335/cube2.png>
What am I doing wrong?
Is there a simple way to get a cube at the origin with it's corners on the
axes?
Mike.
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[Rogier Wolff]

Post by nop head

Post by Aurum
Is there a simple way to get a cube at the origin with it's corners on the

axes?
No it is physically impossible.

Technically correct, but

rotate ([0,atan (sqrt(2)),0])
rotate ([0,0,45])
cube (40, center=true);

is what he was asking for.... I think.

Roger.

Post by nop head

Post by Aurum
Having now subscribed to the mailing list hopefully this will now be posted.
Sorry if it's posted twice.
What I'm trying to do is understand how to get a cube at the origin with
it's corners on the axes.
Firstly, I tried rotating by 45° about x and y with no success.
I then rotated 45° about the X axis with
rotate(45,[1,0,0]){
color("cyan") cube(10,center=true);
}
and looked down the Y axis. What I see is this.
<http://forum.openscad.org/file/t2335/cube1.png>
I now realize that I'm not looking at a square anymore but a rectangle with
sides 10 and 14.14 (10 x root 2) and so to align the corners with the Z axis
I need to rotate by atan(1.414) = 54.7°.
I do this with
rotate(45,[1,0,0]){
rotate(54.7,[0,1,0]){
color("cyan") cube(10,center=true);
}
}
and the result is
<http://forum.openscad.org/file/t2335/cube2.png>
What am I doing wrong?
Is there a simple way to get a cube at the origin with it's corners on the
axes?
Mike.
--
Sent from: http://forum.openscad.org/
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[nop head]

A cube has 8 corners but there are only 6 points if one is on each half
axis.

An object with all corners on an axis has triangular faces and looks like

Post by Rogier Wolff

Post by nop head

Post by Aurum
Is there a simple way to get a cube at the origin with it's corners on

the

Post by nop head
axes?
No it is physically impossible.

Technically correct, but
rotate ([0,atan (sqrt(2)),0])
rotate ([0,0,45])
cube (40, center=true);
is what he was asking for.... I think.
Roger.

Post by nop head

Post by Aurum
Having now subscribed to the mailing list hopefully this will now be posted.
Sorry if it's posted twice.
What I'm trying to do is understand how to get a cube at the origin

with

Post by nop head

Post by Aurum
it's corners on the axes.
Firstly, I tried rotating by 45° about x and y with no success.
I then rotated 45° about the X axis with
rotate(45,[1,0,0]){
color("cyan") cube(10,center=true);
}
and looked down the Y axis. What I see is this.
<http://forum.openscad.org/file/t2335/cube1.png>
I now realize that I'm not looking at a square anymore but a rectangle

with

Post by nop head

Post by Aurum
sides 10 and 14.14 (10 x root 2) and so to align the corners with the Z axis
I need to rotate by atan(1.414) = 54.7°.
I do this with
rotate(45,[1,0,0]){
rotate(54.7,[0,1,0]){
color("cyan") cube(10,center=true);
}
}
and the result is
<http://forum.openscad.org/file/t2335/cube2.png>
What am I doing wrong?
Is there a simple way to get a cube at the origin with it's corners on

the

Post by nop head

Post by Aurum
axes?
Mike.
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[Aurum]

Thank you, it makes sense now. I'm thinking of the axis coming out of each
face and (incorrectly) visualized them coming out of the corners. Actually,
that double pyramid shape will achieve the effect I'm after.
I'm assuming cube(10,10,0.001) gives the pyramid.

Time to play some more.

Thanks all,

Mike.



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[nop head]

Post by Aurum
I'm assuming cube(10,10,0.001) gives the pyramid.

It gives approximately a square. The hull of that and one rotated 90
degrees gives the pyramid.

Hull only works on 3D shapes unfortunately.

Post by Aurum
Thank you, it makes sense now. I'm thinking of the axis coming out of each
face and (incorrectly) visualized them coming out of the corners. Actually,
that double pyramid shape will achieve the effect I'm after.
I'm assuming cube(10,10,0.001) gives the pyramid.
Time to play some more.
Thanks all,
Mike.
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[Hans L]

The double pyramid shape is also known as an octahedron and is one of
the Platonic solids.

Here's another way to make one using "cylinders".
for (k = [0,1]) mirror([0,0,k])
cylinder(r1=1,r2=0,h=1, $fn=4);

Another alternative would be to construct one from points and faces
using the polyhedron module.

Post by Aurum
Thank you, it makes sense now. I'm thinking of the axis coming out of each
face and (incorrectly) visualized them coming out of the corners. Actually,
that double pyramid shape will achieve the effect I'm after.
I'm assuming cube(10,10,0.001) gives the pyramid.
Time to play some more.
Thanks all,
Mike.
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