Though my NXT
3D probe scanner was quite successful, it suffered from
a big drawback: it was slooooow! I then discovered DAVID-3D
laserscanner. This software gem allow to reconstruct
3D shapes with a line laser and a webcam! Even better,
the free version is quite usable with some limitations: resolution
is low, and you have to use MeshLab
to assemble the scans together to rebuild the complete shape.
Even though you can sweep the laser line on
the scanned object by hand, you'll get better scan quality with
a very regular and low speed sweep. I built this NXT contraption
Here you see the heart of the action.
The red laser line slowly sweeps the object (here
a Fabuland lamb head). Behind the scanned object,
two planes with a 90° angle provide reference
to the scanning software. They are also marked with
regularly spaced black dots that serve during the
calibration process that inform scanning software
of webcam characteristics, field of view, optics
The laser sweeping mechanism. The
NXT motor is down-geared by 1:2880, providing a
really slow motion. The two white rubber bands maintain
tension on the gears to avoid gear lash. The NXC
code allows to set the scan speed through motor
speed variation, and to move the laser at maximum
speed during scan setup.
Below the sweeping mechanism there is a Logitech
Pro 9000 webcam. This high quality webcam provides
very good images, thus detailed scans (though I
made my first tries with a much lower cost Trust
webcam). The drawback of this webcam is that it
doesn' have a screw mounting hole, here
is how I added one.
The laser itself is powered from
the NXT through a sensor port. The small interface
board in the middle of the cable contains a transistor
to switch the laser on/off (the same way as the
LED of NXT light sensor) and a series diode to lower
The laser is a red laser module with focused
line that I bought from DealExtreme.
Close-up of the laser control interface.
Schematics of the control interface.
D2 is a small silicon diode (1N4148) whose purpose
is to lower voltage on the laser, since lightly
loaded NXT IO supply can exceed the 4.5V maximum
rating of the laser used. Q1 is a small NPN transistor
(BC548, 2N3904...) used to control laser with DIGI0
NXT I/O pin. This is the same circuitry as the one
used in the LEGO light sensor to control the red
LED, so the laser can be controlled the same way.
Program the port as a reflected light sensor to
light up the laser, and as an ambient light sensor
to put it off.
Top view of the scan bench. The second
NXT motor is able to rotate the object to acquire
different angles of view. It would be necessary
to be able to tilt the object to see above and under.
Unfortunately I have not yet found a way to do this
without blocking camera sight on the panels behind.
So I replace straight axle mount with assemblies
containing angle connectors.
Update: I have built another version
of the scanning hardware that allows tilting of
the object for easy scanning above and below.
is very simple, you first choose scan speed, then
pressing orange button you go to the main scanning
screen..The laser lights up. Pressing the right
or left NXT key allow you to start scan in up or
down direction. Pressing left or right for a more
than one second toggle to high speed mode to pre-position
laser line before actual scan. Pressing orange button
again, you go to the object rotation mode that allows
to turn the object by 45° increments. Orange
again comes back to scan mode.
Here are a few LDraw parts that I created with the help of
Here is a very quick overview of the long and winding road
going from physical LEGO parts to its LDraw model.
Choose the part to model. Geometrical shapes are not
interesting to build through 3D scan, the models created
this way contain a lot of triangles so this process is best
for organic shapes, as you can see in gallery above.
The laser line on the object must be clearly visible
by the camera. The part must be lightly colored and without
patterns. Otherwise you need to "paint" it in
white color. I generally use a chalk spray paint, but white
tempera with a drop of detergent works too. You'll then
need to carefully clean the object after scanning with a
In a darkened room, calibrate your camera (see details
install the object on the scanner and start scanning.
You will need to perform scans from various directions,
to make sure you completely cover the object. Some areas
not covered by scan may be acceptable provided the object
is smooth there, the reconstruction process will fill the
holes. Make sure there is enough overlap between scans to
ease object reconstructions later. Save all the partial
3D views for later processing.
If you have the full version of DAVID, you may use its ShapeFusion
tool to reconstruct the object
load all the partial scans in ShapeFusion
the first step will be to clean the scans, removing
parasitic shapes (eg. the supporting axle) and the fuzzy
edges of the scan where the laser line or camera viewing
direction were almost tangent to the shape.
align all the scans. If there is enough overlap, the
automatic process works well. Otherwise you will need to
use manual alignment tools, much more time consuming...
once you are happy with the patchwork of partial scans,
do a Poisson reconstruction... and you now have the raw
shape, with a huge number of triangles.
If you have only the free version of DAVID,
ShapeFusion doesn't allow you to save the reconstructed result.
You'll have to use MeshLab
for that. I have written a tutorial about that here.
This tutorial is based on an old version of MeshLab, recent
version works better (especially the matching points based alignment
tool). You may have to experiment a bit...
One problem with scanned parts is that the edges are not
as sharp as they should be, because
when looked closely, real part edges are not so sharp
the scanning process has limited resolution
white paint tend to accumulate in the holes, partially
To be able to place outlining LDraw edges, you need to enhance
locally sharpness of the mesh. Sculptris
does wonder for that. Import the mesh you obtained from scan
as a .obj file, and use the crease tool to sharpen angles where
needed. The smooth tool maybe handy too if you see small irregularities
in an area that should be smooth.
The next step with be to down-sample the mesh. Raw scan contains
some 20000 triangles and after Sculptris enhancement this figure
can rise in the 1000000 range. A good value to target for a
LDraw file is about 3000 to 5000 triangles. MeshLab decimation
filter works great for that. Load scanned part in MeshLab, then
apply Filters > Remeshing, simplification and reconstruction
> Quadric Edge Collapse Decimation. Choose the target number
of faces and click apply. Check then if the result is detailed
enough and if you have triangle edges where you intend to place
outlining LDraw edges. Misplaced edges may require to go back
to Sculptris and sharpen the edge even more. If the result is
not detailed enough, you may also increase the number of triangles.
It is also possible to use several different resolutions in
various places of the part. For example, in Dobby's
head the eye appeared blocky and the mouth was blurred.
I first reduced the overall mesh to 10k triangles, selected
eyes and mouth, inverted selection and further reduced mesh
size on selection to 3500 triangles. I then had enough details
in the eyes while keeping mesh size down.
When you are happy with the result, it's time convert to
LDraw. In MeshLab, save the file in stl file format. Don't forget
to uncheck "Binary encoding", then convert the resulting
.stl file to LDraw using Stl2dat.
After that you just have to do regular Parts Tracker preparation,
similar to the one you have to do on LEGO
Universe Team parts...