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Creating LDraw Parts:
Introduction to Creating LDraw Parts
Introduction to Creating LDraw
Parts
Various Authors, extracted from original LDraw FAQ
How can I create a part that is not yet in
LDraw?
First check if somebody else are working on the part. You can do
that on the LDraw.org Parts
Tracker.
Steve Bliss, Jaco van der Molen, and Tore Eriksson present
different approaches to creating parts, and Manfred Moolhuysen has
some detailed advice for using the predefined subparts (without
studying math). But first of all, you should check out which
primitives are available.
When you have finished the part, you should check it for
technical mistakes with l3p -check,
and then send it to parts@ldraw.org so it can
be included in the LDraw.org parts distribution.
Steve Bliss writes:
Hmm. "Directions for making parts".
Hmm. I can't think of directions, so much as advice. I don't really
see how there could be a 1-2-3 cookbook approach. But here are some
thoughts:
When you model a part, you need to think in terms of vertices,
edges and surfaces. Your part-file has to provide one or more
commands for each edge and surface. You need to specify these edges
and surfaces by the XYZ position of their vertices. So you have to
measure out where the vertices are. The trick with lego parts is
that they are (typically) built around the familiar sizes of studs
and plates (and bricks). So you often measure parts by comparing
them to other parts (like simple bricks and plates).
The typical way to start drawing a part is to examine the .DAT
file for a similar part. At least, that's the way *I* do it. ;-)
Doing an LEDIT xxxx.DAT will let you step through each line in the
part-file, so you can see what the effects are. And how other people
have built their parts.
Here are some suggestions on what you should check out as you get
started:
- Study the LDraw language section of the LDraw FAQ. Become very
familiar with the formats, and what they do.
- Expertise with computer graphics methods is very helpful. You
should at least be comfortable with the concepts of rotating,
translating, and scaling, even if you aren't comfortable with the
theory behind them.
- Forget about LEdit, except as a sometimes buggy way of
stepping through the part-files you create. Notepad will be your
friend for creating new parts. I also use Excel, LDraw Add-On's
Inliner, and the little Torus Generator I wrote. If you find
another tool that is helpful for parts-modelling, I'd like to
know!
- Learn what's in the ldraw\p\ directory. This directory
contains a number of subpart files that are useful in different
parts. STUD.DAT is used in almost every LDraw part in existence
(and most of the others use STUD2.DAT). The other files are useful
"synthetic primitives", such as rings, discs, cylinders, and
spheres. Some of them are LEGO-specific, such as PEGHOLE.DAT, and
some are very general, such as 1-4DISC.DAT (BTW, the '1-4' means
1/4).
What kind of instructions/information would you like to see? I'd
be happy to answer questions (and I'm sure others would as well),
but I don't have time to write up a big list of instructions right
now. Tips I can provide, but I hate throwing off a bunch on
context-free information which may or may not be relevant.
Tip #1: The LDraw standard for positioning is to center the piece
on X=0 and Z=0. Usually, the top of the part (excluding studs) is
set to Y=0.
Tip #2: Look for repeated elements in a part, which you can write
up as a sub-part file. I find long lists of LDraw commands to be
very confusing. Using subparts can shorten the file, and make things
more comprehensible. In writing my chain-saw blade, my final version
used 10 custom files. I used the inliner utility to combine all
these files before publishing.
Tip #3: Use the 0 command-line to insert as many comments as you
want. You can always remove them before publishing, if you don't
want everyone to see your notes. This can really help to organise
long files, making it easier to go back and fix sections later.
Tip #4: Notepad is not very good. Wordpad is better. You may have
another editor you like even more.
I can't think of anything else right now. Ask lots of questions.
Steve
Jaco van der Molen writes:
- I made a drawing on paper of the basic points and started
mapping these coordinates.
- Next I used Excel (yes, MS Excel) to define the coordinates of
all other points and combined these into lines and faces.
- To finish the job, I used Editpad to remove the tabs and
replace them by spaces and there I had it!
Sjaacko
Tore Eriksson writes:
While making a part, I often use different colours so that I can
easily see what areas are still to be covered, if a polygon came out
right, and which one didn't.
You can find an example at <URL:http://www.ldraw.org/community/memorial/archive/FAQ/25a.gif>.
When everything is done, it's easy to set all to colour 16 or 24.
Tore
Manfred Moolhuysen writes:
Examining the existing part file of a basic lego brick also helps
you to understand how part files are made.
Most of them use subparts, handy primitive shapes like cylinders,
circles, disks, and the studs that are on top of or inside the
bricks. You find all the available subparts in the subdirectory
P.
The line: 1 16 0 8 0 -6 0 0 0 -12 0 0 0 6 4-4cyli.dat
means you are including a full cylinder wall, a tube with both
ends open. The other #-#cyli.dat subparts are useful if
you want just a part of a cylinder wall, say 3-4cyli.dat for a 270
degrees cylinder part.
The numbers 0 8 0 tells LDraw to place the cylinder
base centred at the point (X = 0, Y = 8, Z = 0), just like the
placing of normal parts.
The 9 numbers following represent combined information about the
dimensions of the cylinder and its orientation in space. In
mathematics it is called a transformation matrix, but luckily for us
we can tackle this in a "you don't have to know math" way.
To put it simply:
- The pure value of the numbers represent the dimensions.
- The distribution of the numbers over the 9 available positions
and the fact if they are positive or negative represent the
orientation.
In this example the cylinder radius is 6 units (= diameter 12).
the two numbers 6 are responsible for that. If those two numbers
were not equal the result would have been a "squeezed" pipe with an
oval cross-section. The 12 says the cylinder is 12 units high or
long.
I have worked out a simple way to deal with the orientation of
subparts, without getting my mind in a numerical twist:
You see, no math at all. It also works for all the other subpart
types.
Some examples and detailed instructions:
Create this file, in the LDRAW\MODELS directory: 0
1 16 0 0 0 6 0 0 0 12 0 0 0 6 4-4CYLI.DAT
0
and name it TEST.DAT. View it in LDRAW and see the result.
now change the file in: 0
1 16 0 0 0 6 0 0 0 24 0 0 0 6 4-4CYLI.DAT
0
View the result in LDRAW again. You will see the cylinder is
twice as long now.
now change the file in: 0
1 16 0 0 0 12 0 0 0 24 0 0 0 12 4-4CYLI.DAT
0
View the result in LDRAW again. You will see the cylinder is
twice as wide now.
now change the file in: 0
1 16 50 24 20 12 0 0 0 24 0 0 0 12 4-4CYLI.DAT
0
View the result in LDRAW again. You will see the cylinder has
been moved to a different spot.
Now you have an idea what the numbers do if you change them:
position 3,4 and 5 were 50 24 20 and control the insertion point
of the subpart.
position 6 to 14 were 12 0 0 0 24 0 0 0 12 and control the size
of the subpart.
Changing the order and the signs of the last 9 numbers turns your
cylinder, so it is pointing in another direction. This is what you
do in LEDIT.
first change file TEST.DAT back in: 0
1 16 0 0 0 12 0 0 0 24 0 0 0 12 4-4CYLI.DAT
0
We set the numbers on positions 3,4 and 5 to 0 0 0, so the
cylinder will turn around its insertion point.
Start LEDIT, press the ESCAPE-key, press F (stands for file) and
L (for load) Type the file name: TEST.DAT.
line: 1 16 0 0 0 12 0 0 0 24 0 0 0 12 4-4CYLI.DAT is
in the middle of the three lines displayed at the top of the screen.
the line above reads START and the line under reads END.
Press ESCAPE again, Press T (for turn) and X (for x-axis). Type
the angle: 90
On the screen it seems the cylinder has disappeared, but if you
press PAGE-UP followed by PAGE-DOWN the cylinder is redrawn in its
new position. As you can see the cylinder is laying on its belly
now.
First save the file: press the ESCAPE-key, press F (for file) and
S (for save). Then open it in your text editor or in windows and cut
and paste the line in the file where you need it.
If you turn the subpart around Z instead of X it is turned into
another direction. Turning around Y is just like spinning the
cylinder around its center, you see no difference at all.
If your file has more than one subpart in it, you can select the
one you are going to turn with the PAGE-DOWN and PAGE-UP keys. It
must be the middle one of the 3 lines displayed at the top of the
screen.
Now try to do something similar with RECT.DAT, make the file 0
1 16 0 0 0 40 0 0 0 1 0 0 0 20 RECT.DAT
0
Just start to play and fiddle a little bit with the numbers on
positions 6, 10 and 14, and see what results you get.
M. Moolhuysen
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