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faq:en_technique

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Technical questions / How does it work

What is the basic scanning procedure?

  1. Setup: Scale the setup according to the object, i.e. place, align and focus the camera (and projector) depending on the scanned object size. Adjust exposure/brightness.
  2. Calibration: Place the 90° calibration corner at the object's location (or similar). Then calibrate the camera (one click). In case of SL scanning, then calibrate the projector (another click).
  3. Scanning: In case of SL, each scan requires one click. In case of laser scanning, the laser line has to be moved slowly over the object by hand. You can collect several scans from different sides of the object. They should overlap.
  4. Texturing: With one additional click (possibly also adjustment of light conditions or camera settings) a texture is grabbed with each scan.
  5. Alignment: One by one, the collected scans are aligned to each other. The user defines the order (which scans are neighbors). As long as the scans overlap sufficiently, the correct alignment is found automatically (no markers necessary).
  6. Fusion: When all scans are aligned, the Fusion (one click) computes one closed triangle mesh without overlappings (possibly textured.)

Do I need calibration panels during scanning?

  • For hand-held laser scanning: YES. After calibration, you need to keep the calibration panels and the camera at a fixed position.
  • For Structured Light scanning. NO. You don't need the calibration board for scanning. After calibration, you can move the whole scanner, but you must not move the camera or projector on the red bar.

What is the best distance between the camera and the object?

As close as possible, so that the camera can see the scanned surface and not much more. For hand-held laser scanning, the camera must also see the two calibration panels in the left and right side of the camera image.

What is the best distance between the camera and the laser/projector?

The intersection angle (angle between camera view direction and laser light plane / projector direction) should be between 15° and 45°.
A rough estimation is: Half as much as the distance between camera and object.

Do we need a dark room for scanning?

Generally darker is better. Direct sunlight is too bright. But some environment light is OK, you don't need pitch black. It is most important that the environment light is CONSTANT during scanning, and the laser (or projector) must be clearly brighter in the camera image than everything else.

Structured Light

How mobile is the SL scanner? When do I need the calibration panels?

SL scanning is always without calibration panels. Those panels are only required for calibration of the scanner. So you would set up the scanner for the desired scan size, fix all screws, then calibrate it.

Then the scanner (on its tripod) can be placed in front of an object and scan surfaces or patches of the size for which it was calibrated (up to 600 mm with the included calibration panels, but more is possible). Larger surfaces should be scanned in small pieces, with overlapping areas, then aligned in the software.

As long as the camera and projector are not moved with respect to each other, and as long as their focus is not changed, the scanner does not need to be re-calibrated.

Laser Scanning

Is it possible to scan the object with a vertical laser line? Instead of moving the laser up and down, we move it from left to the right?

The laser line must be visible in the camera image on the object and on the left and right calibration panel at the same time. Thus the laser line must be rather horizontal.

Do we locate the laser above or below the camera?

Both is possible. After scanning from above, you can often reach some more surface regions from below.
The distance between laser and camera should not be too small (around half as much as the distance between camera and object). The intersection angle (angle between camera view direction and laser light plane) should be between 15° and 45°.

How do I hold and move the laser by hand?

In general, as you like. Practically you should hold your hand at one position and rotate the laser, like this animation shows.
Also please move the laser SLOWLY, not quickly up and down.
In the camera image, the laser line should reach from the left to the right image border, and DAVID must see the laser line on the object in the middle, and on the left and right panels at the same time. The User Manual will help you, e.g. here.

Advanced technical questions

I want to build my own calibration panels. Where can I find the pattern?

The calibration patterns are included as PDF or CDR in the software (download or USB). They can be found in the subfolder “printout”. Also you can find them in your Windows Start menu under Programs → DAVID-Laserscanner3 → Printout.
You can print them in any size, so that it fits to the object you want to scan. Please see the user manual for more information.

How can I perform fully automated 360 degree scanning, e.g with a turntable?

We do not offer fully-automated 360° scanners, but our DAVID software supports self-made solutions. It can send and receive messages over a (virtual) COM port. However you will have to build the mechanics and microcontroller yourself.
Several people on our forum have built individual solutions, e.g. with turntables. They either remote-control DAVID (send commands like Start, Stop, Save from the microcontroller to DAVID), or they let DAVID control the mechanics (send messages from DAVID to the microcontroller, e.g. use the Stop message to trigger a turntable motion).
For more information, please see our page about COM Port and our Forum.
Please note that the Alignment and Fusion of several scans into one 360° result can only be fully automated in DAVID 2.x; please see here.

How can I integrate DAVID's 3D scanning into my own software/hardware environment?

We are currently working on a Software Development Kit (SDK). Coming soon.

Moving the laser by motor

How can it be achieved?

We do not offer motorized laser hardware, but you can build it yourself. You will find several solutions from our forum community.
You will need a microcontroller like the Arduino to commicate with DAVID and drive a stepper motor. One solution is "Katie" by WalterMo and Sven.

Linear motion or rotation?

Both is possible. In general, a rotation is easier and better.

What advantages does it have?

Basically it has the same advantages as Structured Light scanning:

Scanning without background

If your solution is able to repeat exactly the same motion (same start position, same motion speed), you can scan without background. The procedure is to perform one scan of the calibration corner (“Record new motion”) during which the DAVID software learns the laser motion. From then on, repeat the exact same motion during each scan, and you can scan without background (also called “planeless scanning”).

Higher scan quality

A motor can perform an ideal motion without trembling. This usually leads to better scans.

More comfort

Obviously.

How fast should the motor move?

Depends on the resolution and framerate of the camera, and also of the scan quality (resolution) you require.
If you scan too fast, you will get gaps which will be interpolated. In some applications this may be acceptable or even desired.
Ideally the laser should not move faster than one pixel per camera frame, e.g. 15 FPS, 768 pixel rows –> scan should take at least 768/15 = 51 seconds. Usual rotation speeds are between 30 and 180 degree/min.

Is there an SDK?

Not yet, we are working on it.

Can I use two or more cameras / lasers / projectors at the same time?

No. Probably in a future version.

Is there a 64-bit version?

Yes! Since version 3.7, both 32 and 64 bit executables are included.

Is there a Mac or Linux version?

No. Sorry we have no plans for that at the moment. However some people have managed to use DAVID within a virtual machine. Also it seems to be possible to install Windows on a Mac computer using “Bootcamp”. Please understand that we cannot offer support for these systems.

Is the software/manual available in my language?

At this time the software offers English, French, German, Italian, Russian, Spanish. We are working with our distributors to offer more languages. If you would like to help, please contact us.

Technical details

How does laser scanning work internally?

Our paper from 2006, Low-Cost Laser Range Scanner and Fast Surface Registration Approach explains the background.

3D data: What are the X, Y, Z axes?

The origin (0,0,0) lies at the center of the calibration pattern, in the corner.
The X axis lies horizontally inside the right calibration panel.
The Y axis points upward.
The Z axis lies horizontally inside the left calibration panel.

If you have a mobile scanner (e.g. SLS-1) and move it after calibration, the origin and axes will move with the scanner, i.e. stay at the same position relative to the scanner.

DAVID Software Licensing

Free Edition vs. Pro Edition

We offer a Free Edition which can be used by anyone as long as they want. It may be sufficient for many private users. Also please use this version if you'd like to test the compatibility to your hardware (mainly camera). These are the limitations:

  • Single scans: The scans are made with full resolution, but results are saved as OBJ with reduced resolution (losing small details).
  • Shapefusion: You can test the alignment and fusion, but the results here cannot be saved.

Also there is a comparison chart here.

USB vs. Single PC

The software is identical.
The USB version is shipped on a USB key. It does not require any installation, simply plug it into any Windows computer and start DAVID directly from the USB drive. Or, faster, install and run DAVID on your hard disk, but make sure the licensed USB key is plugged in.
The Single PC license can be purchased online. You send us your computer's Registration ID and we create a license file that will work only on that computer. If you need to change your PC one day, we will of course migrate the license for free.

Free Update policy

Our licenses have no time limitation. Each license is valid for one major release version (e.g. Version 3) and can be used with all its minor version updates (e.g. 3.1, 3.2, 3.3, 3.4, 3.5, …). So all minor updates are free.
You can see how DAVID is evolving in our Changelog.

faq/en_technique.txt · Last modified: 2014/06/06 18:38 (external edit)