Subject:
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Re: Quick way to mirror-image a model?
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Newsgroups:
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lugnet.cad, lugnet.cad.mlcad
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Date:
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Wed, 23 Jun 2004 17:52:27 GMT
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Viewed:
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604 times
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In lugnet.cad, Carl Nelson wrote:
> > Check how I do it in my code. You'll probably have to fetch L3Math.c
> > and L3Def.h from the ldglite CVS archive on the sourceforge to see
> > the order, because I think I only put the new stuff in the mirwiz.zip
> > file.
>
> Looks like you're doing MF = MP * (MC * ME) in the code?
Yes, that looks right.
The other thing that messes me up with LDRAW matrices is the row,
column ordering. The ordering in LDRAW files is not what I would
have chosen, so I always have to look it up. From the old FAQ:
http://www.ldraw.org/OLD/community/memorial/archive/FAQ/
Line type 1's format is:
Line Format:
1 colour x y z a b c d e f g h i part.dat
Fields a through i are orientation & scaling parameters, which can be
used in 'standard' 3D transformation matrices. Fields x, y and z also
fit into this matrix:
| a d g 0 |
| b e h 0 |
| c f i 0 |
| x y z 1 |
so that every point (x, y ,z) gets transformed to (x', y', z') :
x' = a*x + b*y + c*z + x
y' = d*x + e*y + f*z + y
z' = g*x + h*y + i*z + z
or, in matrix-math style:
| a d g 0 |
| X' Y' Z' 1 | = | X Y Z 1 | x | b e h 0 |
| c f i 0 |
| x y z 1 |
Now, I'm not actually sure what the row-column order is in the
MLCAD.INI file. Since (x,y,z) was moved to last, maybe the 3x3
is laid out in rows instead of columns. I suppose we should get
that clarified so we use the same format in the MIRROR.INI file.
Here's what MLCAD.INI says:
; <Matrix> a rotation matrix a11 a12 a13 ... a33 for optimal appearance
; at 0 degree rotation angle
; <Offset> The offset of the part to be in place
I don't know if a12 is b, or if a21 is b. It looks like this in the file:
"Cap" "4485.DAT" 0 1 0 0 0 1 0 0 0 1 0 0 0
Is that a b c d e f g h i x y z ???
Or is it a d g b e h c f i x y z ???
Don
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Message has 2 Replies:
 | | Re: Quick way to mirror-image a model?
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| (...) Total side note: I agree with Don, row/column ordering is not what I would have chosen. BUT, it is far easier (IMO) to hand-transform row/column LDraw commands than the equivalent column/row commands (like I've had to do in POV-Ray code). (...) (20 years ago, 23-Jun-04, to lugnet.cad, lugnet.cad.mlcad)
| | | Re: Quick way to mirror-image a model?
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| Hi Don, now it's getting interesting ... "Don Heyse" <dheyse@hotmail.spam....away.com> schrieb im Newsbeitrag news:HzrwBF.9t2@lugnet.com... <SNIP> (...) I'm actually reading it in as | a b c | | d e f | | g h i | and that is also how I'm writing my (...) (20 years ago, 24-Jun-04, to lugnet.cad, lugnet.cad.mlcad)
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Message is in Reply To:
| | Re: Quick way to mirror-image a model?
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| (...) It's neither commutative [(a * b) * c != a * (b * c)] nor associative [a * b != b * a]. That shouldn't be the problem in the calculation above, since the current matrix was the identity matrix... (...) Looks like you're doing MF = MP * (MC * (...) (20 years ago, 23-Jun-04, to lugnet.cad)
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