Mirror operator
This subject comes up every few years.
For a long time I thought the best way to deal with this is to add an
option mirror(v,keep=fales/true).
In the hope that this will it make it easier for people to learn OpenSCAD
and to have shorter code.
On 16. mars 2017 17:24, Peter Falke wrote:
This subject comes up every few years.
For a long time I thought the best way to deal with this is to add an
option mirror(v,keep=fales/true).
In the hope that this will it make it easier for people to learn
OpenSCAD and to have shorter code.
I don't think so, it would solidify confusion unless you want to do the
same for translate, rotate, scale and mirror. And multmatrix too.
These are all just variants of the same thing: different ways of
expressing a transformation via a 4x4 homogeneous transformation matrix.
They all simply transform the object to which the transformation is
applied, no children left behind.
Carsten Arnholm
I would disagree that it "solidifies confusion".
I think the confusion is inherent in the name "mirror".Scale, rotate, and translate do not carry the same basic connotation (that "mirror" does) of "creating a copy".To me "reflect" would have been less confusing. Far more confusing to this new user, was the combination of the words and the illustrations used in the example.
Sent from my U.S. Cellular® Smartphone
-------- Original message --------From: "cacb [via OpenSCAD]" ml-node+s1091067n20936h19@n5.nabble.com Date: 3/16/17 11:59 AM (GMT-08:00) To: jim_klessig jim.klessig@gmail.com Subject: Re: Mirror operator
On 16. mars 2017 17:24, Peter Falke wrote:
This subject comes up every few years.
For a long time I thought the best way to deal with this is to add an
option mirror(v,keep=fales/true).
In the hope that this will it make it easier for people to learn
OpenSCAD and to have shorter code.
I don't think so, it would solidify confusion unless you want to do the
same for translate, rotate, scale and mirror. And multmatrix too.
These are all just variants of the same thing: different ways of
expressing a transformation via a 4x4 homogeneous transformation matrix.
They all simply transform the object to which the transformation is
applied, no children left behind.
Carsten Arnholm
OpenSCAD mailing list
[hidden email]
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
If you reply to this email, your message will be added to the discussion below:
http://forum.openscad.org/Mirror-operator-tp20900p20936.html
To unsubscribe from Mirror operator, click here.
NAML
--
View this message in context: http://forum.openscad.org/Mirror-operator-tp20900p20937.html
Sent from the OpenSCAD mailing list archive at Nabble.com.
I do not understand the confusion.
A real life mirror do not create two images. What you see is a mirror image, but you do not see the original object.
So why OpenSCAD should be different? you apply mirror() to an object, and you get the mirror image, not the original object. Nothing is wrong with that.
My $0.02,
Jean-Paul
N1JPL
On Mar 16, 2017, at 7:19 PM, jim_klessig jim.klessig@gmail.com wrote:
I would disagree that it "solidifies confusion".
I think the confusion is inherent in the name "mirror".
Scale, rotate, and translate do not carry the same basic connotation (that "mirror" does) of "creating a copy".
To me "reflect" would have been less confusing. Far more confusing to this new user, was the combination of the words and the illustrations used in the example.
Sent from my U.S. Cellular® Smartphone
-------- Original message --------
From: "cacb [via OpenSCAD]" <[hidden email]>
Date: 3/16/17 11:59 AM (GMT-08:00)
To: jim_klessig <[hidden email]>
Subject: Re: Mirror operator
On 16. mars 2017 17:24, Peter Falke wrote:
This subject comes up every few years.
For a long time I thought the best way to deal with this is to add an
option mirror(v,keep=fales/true).
In the hope that this will it make it easier for people to learn
OpenSCAD and to have shorter code.
I don't think so, it would solidify confusion unless you want to do the
same for translate, rotate, scale and mirror. And multmatrix too.
These are all just variants of the same thing: different ways of
expressing a transformation via a 4x4 homogeneous transformation matrix.
They all simply transform the object to which the transformation is
applied, no children left behind.
Carsten Arnholm
OpenSCAD mailing list
[hidden email]
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
If you reply to this email, your message will be added to the discussion below:
http://forum.openscad.org/Mirror-operator-tp20900p20936.html
To unsubscribe from Mirror operator, click here.
NAML
View this message in context: Re: Mirror operator
Sent from the OpenSCAD mailing list archive at Nabble.com.
OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
I do not understand the confusion.
A real life mirror do not create two images. What you see is a mirror image, but you do not see the original object.
So why OpenSCAD should be different? you apply mirror() to an object, and you get the mirror image, not the original object. Nothing is wrong with that.
My $0.02,
Jean-Paul
N1JPL
On Mar 16, 2017, at 7:19 PM, jim_klessig jim.klessig@gmail.com wrote:
I would disagree that it "solidifies confusion".
I think the confusion is inherent in the name "mirror".
Scale, rotate, and translate do not carry the same basic connotation (that "mirror" does) of "creating a copy".
To me "reflect" would have been less confusing. Far more confusing to this new user, was the combination of the words and the illustrations used in the example.
Sent from my U.S. Cellular® Smartphone
-------- Original message --------
From: "cacb [via OpenSCAD]" <[hidden email]>
Date: 3/16/17 11:59 AM (GMT-08:00)
To: jim_klessig <[hidden email]>
Subject: Re: Mirror operator
On 16. mars 2017 17:24, Peter Falke wrote:
This subject comes up every few years.
For a long time I thought the best way to deal with this is to add an
option mirror(v,keep=fales/true).
In the hope that this will it make it easier for people to learn
OpenSCAD and to have shorter code.
I don't think so, it would solidify confusion unless you want to do the
same for translate, rotate, scale and mirror. And multmatrix too.
These are all just variants of the same thing: different ways of
expressing a transformation via a 4x4 homogeneous transformation matrix.
They all simply transform the object to which the transformation is
applied, no children left behind.
Carsten Arnholm
OpenSCAD mailing list
[hidden email]
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
If you reply to this email, your message will be added to the discussion below:
http://forum.openscad.org/Mirror-operator-tp20900p20936.html
To unsubscribe from Mirror operator, click here.
NAML
View this message in context: Re: Mirror operator
Sent from the OpenSCAD mailing list archive at Nabble.com.
OpenSCAD mailing list
Discuss@lists.openscad.org
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
On 2017-03-17 00:19, jim_klessig wrote:
I would disagree that it "solidifies confusion".
I think the confusion is inherent in the name "mirror".
Scale, rotate, and translate do not carry the same basic connotation
(that "mirror" does) of "creating a copy".
To me "reflect" would have been less confusing. Far more confusing to
this new user, was the combination of the words and the illustrations
used in the example.
The words translate, rotate, scale and mirror are universal terms in the
context of 3d transformations expressed as 4x4 homogeneous
transformation matrices, just look up any book on transformations in
computer graphics, CAD systems, or finite elements. OpenSCAD has simply
adopted the established nomenclature and interpretation. Applying a new
meaning to these terms would indeed cause more confusion.
Carsten Arnholm
That argument doesn't quite fly for me. In most cad systems I have ever used, a mirror operation, creates a mirror imaged copy. In many cases with the option of deleting or keeping the original.
The mere fact that we are even having this discussion, illustrates that there EXISTS a "confusion", no matter what it's origination.
Sent from my U.S. Cellular® Smartphone
-------- Original message --------From: "cacb [via OpenSCAD]" ml-node+s1091067n20943h36@n5.nabble.com Date: 3/17/17 12:01 AM (GMT-08:00) To: jim_klessig jim.klessig@gmail.com Subject: Re: Mirror operator
On 2017-03-17 00:19, jim_klessig wrote:
I would disagree that it "solidifies confusion".
I think the confusion is inherent in the name "mirror".
Scale, rotate, and translate do not carry the same basic connotation
(that "mirror" does) of "creating a copy".
To me "reflect" would have been less confusing. Far more confusing to
this new user, was the combination of the words and the illustrations
used in the example.
The words translate, rotate, scale and mirror are universal terms in the
context of 3d transformations expressed as 4x4 homogeneous
transformation matrices, just look up any book on transformations in
computer graphics, CAD systems, or finite elements. OpenSCAD has simply
adopted the established nomenclature and interpretation. Applying a new
meaning to these terms would indeed cause more confusion.
Carsten Arnholm
OpenSCAD mailing list
[hidden email]
http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
If you reply to this email, your message will be added to the discussion below:
http://forum.openscad.org/Mirror-operator-tp20900p20943.html
To unsubscribe from Mirror operator, click here.
NAML
--
View this message in context: http://forum.openscad.org/Mirror-operator-tp20900p20944.html
Sent from the OpenSCAD mailing list archive at Nabble.com.
Parkinbot wrote
besides the fact that it has really some funny implementation.
Comming back to the utility of mirror. As a reflection, two subsequent
mirrors are equivalent to a rotation:
// rotate children about x axis
module rotX(a)
mirror([0,cos(a/2),sin(a/2)]) mirror([0,1,0]) children();
Although this usually have little interest, there are cases where the
rotation angle computation may be avoided by using mirror. For instance when
we need the minimum angle rotation that brings a direction d0 to a direction
d1:
module rotFromTo(d0,d1)
mirror(unit(d1)+unit(d0)) mirror(d0) children();
function unit(v) = v/norm(v);
This minimum angle rotation is part of the line definition in Drawing
"lines" in OpenSCAD
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Tips_and_Tricks#Drawing_.22lines.22_in_OpenSCAD
that could be rephrased as:
module line(p0, p1, diameter=1) {
v = p1-p0;
translate(p0)
// rotate the cylinder so its z axis is brought to direction v
rotFromTo([0,0,1],v))
cylinder(d=diameter, h=norm(v), $fn=4);
}
However, thanks to the cylinder symmetries a simpler and more general
polyline may use just one mirror:
module polyline(p,t=1) {
for(i=[0:len(p)-2])
translate(p[i+1])
mirror([0,0,1]+unit(p[i+1]-p[i]))
cylinder(r=t,h=norm(p[i+1]-p[i]));
}
n=500;
k=50;
spiral = [for(i=[0:n])
[cos(-90+180i/n)cos(360i/k),
cos(-90+180i/n)sin(360i/k),sin(-90+180i/n)]];
polyline(20spiral,t=1);
http://forum.openscad.org/file/n20960/SphereSpiral.png
Don't try to render it!
--
View this message in context: http://forum.openscad.org/Mirror-operator-tp20900p20960.html
Sent from the OpenSCAD mailing list archive at Nabble.com.