Subject:
|
Re: LDraw File Format Spec 1.0 DRAFT - Call for Public Comments
|
Newsgroups:
|
lugnet.cad
|
Date:
|
Wed, 22 Aug 2007 21:52:49 GMT
|
Viewed:
|
5327 times
|
| |
|
|
In lugnet.cad, Rob Ross wrote:
> What I meant was, I am confused by the (apparent) difference in what the
> *current* spec says on this issue, and what the new proposed spec says.
>
> If you will look at the current spec and scroll down near the end to the Line
> Format header, you'll see this:
>
>
> 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 |
>
>
>
> Which seems to be an example showing column-major ordering.
Yes, but look where the x, y, and z are. The example matrix is transposed vs
the "standard" one shown in OpenGL text. If you swap the rows and columns in
the above matrix, you'll get the OpenGL one. It's an alternate way of
expressing a 3D matrix that assumes a different layout for the vectors that get
transformed, but the results are the same. That's what I was saying. In my
response to Leonardo I provided a proposed clarification. Let me know what you
think of it.
> So my question about this is, is the spec really changing the ordering of all
> matrices, OR was this just wrong in the original spec?
Neither. It's just a question of wording. As long as you put the X, Y, and Z
in the appropriate place (and the 0s in the other appropriate spots), and as
long as you do your transformations correctly, both ways produce the same
results.
--Travis
|
|
Message has 1 Reply:
Message is in Reply To:
55 Messages in This Thread:
 
 
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
This Message and its Replies on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
