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I confess that I do not really understand the working of a matrix.
Consider the following piece of code:
//start code
#declare P1 = <-1.6, 0.0, 0>;
#declare P2 = < 1.6, 0.8, 0>;
#local Point =
sphere {
<0,0,0>, 0.05
}
object {Point translate P1 pigment {rgb <1,0,0>}}
object {Point translate P2 pigment {rgb <1,1,0>}}
#declare Segment =
box {<-0.10, 0.00, -0.010>, <0.00, 1.00, 0.010>}
#local a = 0;
#local b = VDist(P1,P2);
union {
#while (a <= b)
object {Segment
translate <0, a, 0>
#if (even(a))
pigment {rgb <0,1,0>}
#else
pigment {rgb <0,0,1>}
#end
#local a=a+1;
}
#end
clipped_by {plane {y, b}}
matrix <1, (P1.y-P2.y), 0, // matrix-shear_x_to_y
0, 1, 0,
0, 0, 1,
0, 0, 0>
Point_At_Trans(P2-P1)
translate P1
}
//end code
What I want is that the short sides of the Segment always remain
vertical whatever the positions of P1 or P2. What am I doing wrong?
Thanks for any help,
Thomas
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I'm not quite sure what you are doing, so i can't tell you what you are doing
wrong.
My guess is, that you need to transpose the upper 3x3 portion of your matrix,
that is, use
matrix <1, 0, 0,
(P1.y-P2.y), 1, 0,
0, 0, 1,
0, 0, 0>
instead.
You could also try the Shear_Trans() and/or Matrix_Trans() macros in
transforms.inc instead, which are probably easier to use.
Regards Roman
Thomas de Groot <tDOTdegrootATinterDOTnlDOTnet> wrote:
> I confess that I do not really understand the working of a matrix.
> Consider the following piece of code:
>
> //start code
> #declare P1 = <-1.6, 0.0, 0>;
> #declare P2 = < 1.6, 0.8, 0>;
>
> #local Point =
> sphere {
> <0,0,0>, 0.05
> }
>
> object {Point translate P1 pigment {rgb <1,0,0>}}
> object {Point translate P2 pigment {rgb <1,1,0>}}
>
> #declare Segment =
> box {<-0.10, 0.00, -0.010>, <0.00, 1.00, 0.010>}
>
> #local a = 0;
> #local b = VDist(P1,P2);
>
> union {
> #while (a <= b)
> object {Segment
> translate <0, a, 0>
> #if (even(a))
> pigment {rgb <0,1,0>}
> #else
> pigment {rgb <0,0,1>}
> #end
> #local a=a+1;
> }
> #end
> clipped_by {plane {y, b}}
> matrix <1, (P1.y-P2.y), 0, // matrix-shear_x_to_y
> 0, 1, 0,
> 0, 0, 1,
> 0, 0, 0>
> Point_At_Trans(P2-P1)
> translate P1
> }
> //end code
>
> What I want is that the short sides of the Segment always remain
> vertical whatever the positions of P1 or P2. What am I doing wrong?
>
> Thanks for any help,
>
> Thomas
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Thomas de Groot <tDOTdegrootATinterDOTnlDOTnet> wrote:
....
> What I want is that the short sides of the Segment always remain
> vertical whatever the positions of P1 or P2. What am I doing wrong?
>
> Thanks for any help,
>
> Thomas
Did you see the new winpov insert menu/Transformation/matrix_shear...
examples with pictures.
Do these help?
Stephen S
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On 13-7-2011 23:06, StephenS wrote:
> Thomas de Groot<tDOTdegrootATinterDOTnlDOTnet> wrote:
> ....
>> What I want is that the short sides of the Segment always remain
>> vertical whatever the positions of P1 or P2. What am I doing wrong?
>>
>> Thanks for any help,
>>
>> Thomas
>
> Did you see the new winpov insert menu/Transformation/matrix_shear...
> examples with pictures.
>
> Do these help?
>
> Stephen S
>
>
Yes, that is basically where my matrix is coming from:
matrix<1, 0.5, 0, // matrix-shear_x_to_y
0, 1, 0,
0, 0, 1,
0, 0, 0>
The difficulty is that, not only the object at P1 needs to point_at P2,
which is not difficult to do, but also has to be sheared in such a way
that the short sides remain vertical.
Maybe I am making a wrong assumption somewhere....
THomas
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No, the matrix is correct for shearing vertically, which is my
intention, like from the Insert Menu:
matrix <1, 0.5, 0, // matrix-shear_x_to_y
0, 1, 0,
0, 0, 1,
0, 0, 0>
Where I am going wrong, I guess is by using Point_At_Trans(), instead of
Reorient_Trans(). Still, I am not out of the wood :-(
I rewrote my code accordingly and I am sure it is the 0.5 in the matrix
that should be replaced by a variable based on P1 and P2, but I am
really at a loss what that should be.
Try this new code which is more towards what I intend to do:
//Start Code
#local P1 = <-1.6, 0.1, 0>;
#local P2 = < 1.7, 1.5, 0>;
#local Point =
sphere {
<0,0,0>, 0.05
}
object {Point}
object {Point translate P1 pigment {rgb <1,0,0>}}
object {Point translate P2 pigment {rgb <1,1,0>}}
#local Segment =
box {<0.00, 0.00, -0.010>, <1.00, 0.10, 0.010>}
#local a = 0;
#local b = VDist(P1,P2);
union {
#while (a < b)
object {Segment
translate <a, 0, 0>
#if (even(a))
pigment {rgb <0,1,0>}
#else
pigment {rgb <0,0,1>}
#end
#local a=a+1;
}
#end
clipped_by {plane {x, b}}
matrix <1, 0.5, 0, // matrix-shear_x_to_y
0, 1, 0,
0, 0, 1,
0, 0, 0>
Reorient_Trans (<P1.x,0,P1.z>, <-P2.x, 0, -P2.z>)
translate P1
}
//End Code
If you increase or decrease the 0.5 value, you will see the shearing
increasing or decreasing, while the short sides remain vertical like I
want. Only, now the problem is to keep the object's far end at the P2
location :-(
The info about Shear_Trans() and Matrix_Trans() is so succinct (for me)
that I cannot do anything with it. My math knowledge is clearly to low
for this.
Thomas
On 13-7-2011 16:34, Roman Reiner wrote:
> I'm not quite sure what you are doing, so i can't tell you what you are doing
> wrong.
> My guess is, that you need to transpose the upper 3x3 portion of your matrix,
> that is, use
>
> matrix<1, 0, 0,
> (P1.y-P2.y), 1, 0,
> 0, 0, 1,
> 0, 0, 0>
>
> instead.
>
> You could also try the Shear_Trans() and/or Matrix_Trans() macros in
> transforms.inc instead, which are probably easier to use.
>
> Regards Roman
>
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Like this?
//Start Code
#local P1 = <-1.6, 0.1, 0>;
#local P2 = < 1.7, 1.5, 0>;
#local Point =
sphere {
<0,0,0>, 0.05
pigment { rgb 1 }
}
object {Point}
object {Point translate P1 pigment {rgb <1,0,0>}}
object {Point translate P2 pigment {rgb <1,1,0>}}
#local Segment =
box {<0.00, 0.00, -0.010>, <1.00, 0.10, 0.010>}
#declare d = P2-P1;
#local a = 0;
#local b = d.x;
union {
#while (a < b)
object {Segment
translate <a, 0, 0>
#if (mod(a,2)=0)
pigment {rgb <0,1,0>}
#else
pigment {rgb <0,0,1>}
#end
#local a=a+1;
}
#end
clipped_by {plane {x, b}}
matrix <d.x/b, d.y/b, 0, // matrix-shear_x_to_y
0, 1, 0,
0, 0, 1,
0, 0, 0>
translate P1
}
//End Code
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BTW, i killed that Reorient_Trans since it does nothing. As P1.z and P2.z are
zero those two: <P1.x,0,P1.z>, <-P2.x, 0, -P2.z> are parallel (pointing in
opposite directions) resulting in the Reorient_Trans macro to return an empty
transform.
Regards Roman
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On 14-7-2011 11:06, Roman Reiner wrote:
> BTW, i killed that Reorient_Trans since it does nothing. As P1.z and P2.z are
> zero those two:<P1.x,0,P1.z>,<-P2.x, 0, -P2.z> are parallel (pointing in
> opposite directions) resulting in the Reorient_Trans macro to return an empty
> transform.
>
> Regards Roman
>
>
Yes, that works, but only because z remains 0 in your code. That is why
I am not too sure about not using VDist(). The Reorient_Trans() is
necessary for those cases where P2 (and/or P1) moves also along the
z-axis. Or is there another way? The code should be valid for *all* 3D
locations of P1 and P2.
Thomas
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In that case it should read Reorient_Trans(<1,0,0>, <d.x, 0, d.z>) where d is,
again, P2-P1.
Also b = d.x needs to be replaced with b = vlength(<d.x, 0, d.z>).
Altogether:
//Start Code
#local P1 = <-1.6, 0.1, -.5>;
#local P2 = < 1.7, 1.5, 1>;
#local Point =
sphere {
<0,0,0>, 0.05
pigment { rgb 1 }
}
object {Point}
object {Point translate P1 pigment {rgb <1,0,0>}}
object {Point translate P2 pigment {rgb <1,1,0>}}
#local Segment =
box {<0.00, 0.00, -0.010>, <1.00, 0.10, 0.010>}
#declare d = P2-P1;
#local a = 0;
#local b = vlength(<d.x, 0, d.z>);
union {
#while (a < b)
object {Segment
translate <a, 0, 0>
#if (mod(a,2)=0)
pigment {rgb <0,1,0>}
#else
pigment {rgb <0,0,1>}
#end
#local a=a+1;
}
#end
clipped_by {plane {x, b}}
matrix <1 d.y/b, 0,
0, 1, 0,
0, 0, 1,
0, 0, 0>
Reorient_Trans(x, d*(1-y)) //short for Reorient_Trans(<1,0,0>, <d.x, 0, d.z>)
translate P1
}
//End Code
[Note, that the above version shears the segments by dragging the far end up
resulting in the originally unit length segments to get longer. If you want them
to remain at unit length you need to use
clipped_by {plane {x, vlength(d)}}
matrix <b/vlength(d) d.y/vlength(d), 0,
0, 1, 0,
0, 0, 1,
0, 0, 0>
instead.]
Feel free to ask if you need any explanations!
Regards Roman
Thomas de Groot <tenDOTlnDOTretniATtoorgedDOTt> wrote:
> Yes, that works, but only because z remains 0 in your code. That is why
> I am not too sure about not using VDist(). The Reorient_Trans() is
> necessary for those cases where P2 (and/or P1) moves also along the
> z-axis. Or is there another way? The code should be valid for *all* 3D
> locations of P1 and P2.
>
> Thomas
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Thank you Roman, for your help! This works fine.
One question: you use vlength() instead of VDist() and seem not to take
into account the y-component. However, it seems to me that between P1
and P2 the y-component can potentially be of importance especially if
height differences are large. Would that not be compensated by VDist()?
Or vlength(d)?
Thomas
On 14-7-2011 14:08, Roman Reiner wrote:
> In that case it should read Reorient_Trans(<1,0,0>,<d.x, 0, d.z>) where d is,
> again, P2-P1.
>
> Also b = d.x needs to be replaced with b = vlength(<d.x, 0, d.z>).
>
> Altogether:
>
> //Start Code
> #local P1 =<-1.6, 0.1, -.5>;
> #local P2 =< 1.7, 1.5, 1>;
>
> #local Point =
> sphere {
> <0,0,0>, 0.05
> pigment { rgb 1 }
> }
>
> object {Point}
> object {Point translate P1 pigment {rgb<1,0,0>}}
> object {Point translate P2 pigment {rgb<1,1,0>}}
>
> #local Segment =
> box {<0.00, 0.00, -0.010>,<1.00, 0.10, 0.010>}
>
> #declare d = P2-P1;
>
> #local a = 0;
> #local b = vlength(<d.x, 0, d.z>);
> union {
> #while (a< b)
> object {Segment
> translate<a, 0, 0>
> #if (mod(a,2)=0)
> pigment {rgb<0,1,0>}
> #else
> pigment {rgb<0,0,1>}
> #end
> #local a=a+1;
> }
> #end
> clipped_by {plane {x, b}}
> matrix<1 d.y/b, 0,
> 0, 1, 0,
> 0, 0, 1,
> 0, 0, 0>
> Reorient_Trans(x, d*(1-y)) //short for Reorient_Trans(<1,0,0>,<d.x, 0, d.z>)
> translate P1
> }
> //End Code
>
> [Note, that the above version shears the segments by dragging the far end up
> resulting in the originally unit length segments to get longer. If you want them
> to remain at unit length you need to use
>
> clipped_by {plane {x, vlength(d)}}
> matrix<b/vlength(d) d.y/vlength(d), 0,
> 0, 1, 0,
> 0, 0, 1,
> 0, 0, 0>
>
> instead.]
>
> Feel free to ask if you need any explanations!
> Regards Roman
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