(click here to get to DAVID 2.x User Manual)
Structured Light Scanning (SL) is 3D scanning with a video projector instead of the laser. DAVID will use the video projector to project a number of stripe patterns onto the object. The camera will watch that from a different point of view (above, below, left or right of the projector) and take (at least) one image of each pattern. Based on the deformations of the stripe patterns in these images, DAVID will compute a precise 3D mesh of the object surface.
Camera calibration is the same as for laser scanning. Scanning however is much faster and simpler:
Mobile scanner: It is easily possible to mount camera and projector with a fixed distance to one stand (e.g. tripod). Once calibrated, this mobile scanner can be moved and scan anywhere, as long as camera and projector remain fixed and their optics remain unchanged.
Connect your projector to your PC (usually via VGA, DVI, HDMI, or DisplayPort).
Short story: Set up your projector as extended desktop (screen 2). Set both your monitor and projector to their respective native resolution. Go to Step 2.
Long story: Windows does not make a difference between a projector and a monitor: Both are “screens” or “displays” with a certain resolution. It can be set to show the same content on both (clone), or different content (extended desktop) that expands from one screen to the other. That's what we need! Icons, program windows and mouse pointer etc. can be placed on either screen, or moved from one to the other. The only thing that is “cloned” on both displays is your desktop background image.
Fast version: In Windows 7, you can press Win+P to get a menu like this. Choose “Extend”, usually then you are done:
In any Windows version, you can right-click on your desktop and choose “Properties” or “Screen Resolution” (depending on your Windows version).
Choose “Extend”, and set each display to its native resolution (maximum). You can click “Identify” to see which is which. Also you can choose which is your “main display” (should be your monitor).
Move your mouse pointer around toward the display borders to see how it leaves one display and appears on the other. You can move any windows, desktop icons or even the taskbar where you want, but usually you will want them all on your monitor.
We recommend to disable all filters that your projector may have for image “improvement”, like increased sharpness or contrast, frame interpolation etc.
Choose a calibration pattern that fits your object size / desired scan volume. If possible, place the object in the corner and let the camera and projector point into the corner.
The projector must be placed left, right, above or below the camera (e.g. the projector on the table and the camera well spaced above the projector, or next to it, or…). The illumination should be similar to the camera view, at least cover the calibration corner area that you want to scan later. Structured Light is based on triangulation, so many things are similar to laser scanning. Please make sure that you have a sufficient triangulation angle between camera viewing axis and illumination axis.
This image shows a perfect setup:
On the following image the sine waves are distorted (over-saturated). This will cause waves in the scan result. Avoid this by decreasing camera exposure or brightess. If that is not possible, you can decrease the projector brightness with the slider at the top.
The next image is too dark. In this case increase camera exposure and/or brightness.
Remove the object from the scene, so the camera can see the calibration corner. It does not need to see ALL markers.
At the left, open the Camera Calibration menu, enter the correct calibration scale, and calibrate your camera. Fore more information please see this page.
Like the camera, the projector must be calibrated, i.e. DAVID must know its location, viewing direction, focal length, lens distortion etc. We use the same calibration panels like for camera calibration. The markers are not used, but the flat panels must be at the same position as during camera calibration! So we recommend you to perform camera and projector calibration always in succession without moving anything.
At the left, open the Structured Light menu. There are presets “Quality”, “Default”, and “Speed” that mainly influence the number of patterns used for scanning. A larger number of patterns usually gives better scan quality at the cost of a longer scanning time. For most cases “Default” is recommended.
Click “Calibrate Projector” and wait a few seconds. The whole pattern sequence will now be projected and captured by the camera. After a while you should see a debug image popping up that shows a phase error (i.e. phase deviation & compensation curve). This image is not easy to interpret so do not hesitate to close it. If you are and advanced user and try to optimize your SL results, please read "How to interpret the Phase Deviation & Compensation Curve".
Afterwards, your scanner is calibrated! You can remove the calibration panels, but keep your camera and projector fixed to each other and don't change the optics (focus, zoom).
Once you move camera or projector, or change focus (e.g. if you want to scan something much smaller or larger), or if you are not sure, you will have to calibrate the camera and the projector again.
Place the object in front of the scanner, or (mobile scanner) place the object in front of the object / region of interest.
Click “Start”, wait a few seconds, there is your scan result!
If you activate “Auto. grab texture”, DAVID will grab a texture for this scan immediately after the scan. It will use the camera and projector settings that you have set previously in the Texturing Menu, so it is recommended to go there first and adjust the settings.
Please note that good scan results are only possible for object sizes and at distances in front of the scanner that are similar to the conditions during calibration. If you need to scan much larger or much smaller spaces, you will have to set up and re-calibrate camera and projector (usually with a larger or smaller calibration pattern) for best results.
Usually you don't need to worry about these parameters. Just choose one of the Parameter Presets “Quality”, “Default”, or “Speed”, depending on your requirements.
There are several SL parameters that you can change (some in Advanced Settings). Most influence the Total Number of patterns, and thus the scan time and quality. In general: More patterns = more time, but better results. When you change a parameter, you will usually have to calibrate the projector again. Here are the ones you might want to play with, the most important ones are bold:
