Calibration

Projector Setup

Start DAVID by running “Start_DAVID3_x64” from the USB flash drive. If you wish to update your software to the latest version, go to www.david-3d.com to download the most updated version. If you use 32-bit system (not recommended), run “Start_DAVID3”. 

The DAVID-LASERSCANNER interface window will be opened up. On the left hand side:

1. Select "DAVID SLS-2" as your setup type.
2. Set up the Screen ID so that the stripe pattern is shown on your projector. (usually 2)
3. Choose the camera you are using for the 3D Scan.
4. 

Scan Object Setup

DAVID measures the image intensities along 3 horizontal and 3 vertical lines and displays them as red curves. It is very important to find good settings so that these red curves are well saturated. Regard those image regions that show the wave patterns: The red intensity curves must be sinusoidal and must not be over- or under-saturated. In other words, the red sine curve must not be cut off at the blue borders.

(insert one or two sets of 3 images showing how redlines/sine curves work)

 Image image image

To achieve the best result, please carefully adjust the following settings:

• Working Distance 
  Place the scan object in front of the projector. Adjust the working distance to make sure the screen projected from the projector covers the entire object, not less, not much more either.  (insert an image of a scan object with illuminated stripes on the body) Working Distance is the distance between the object to be scanned and the projector.   (insert an image of working distance)

• Projector focus
  Dial “focal ring” located on top of the projector to focus the projected stripped image on the scan object. Depending on your projector model, if the projector is perfectly focused, the fine lines between the projector's pixels may cause a fine noise in the scan. If that happens, we recommend to set the projection slightly out of focus. This will not reduce the scan quality. (insert an image of projector focal ring)

• Position of the camera
  To adjust the location and angle of the camera, loose the thumbscrew on the bottom of the camera to slide it. Position the camera so that the projected pattern on the object surface (nearly) fills the camera view. If the camera view shows much more than the scanned surface, you should reduce the distance between camera and object. Fix the ball joint (where available). Adjust camera focus to get a sharp image Make sure the screws are tightened up once the location is adjusted. (insert an image of thumbscrew)
  

• Exposure time
  The Exposure should be set to the same value as the frame rate of the projector (usually 1/60s), otherwise the camera image will flicker/pulsate when looking at the projection.

• Camera focus
  Adjust the aperture of the camera so that you will get a rather bright picture. Look at the camera image and watch the sharpness of the object and the sharpness of the projected black and white stripes. Dial the camera focus to get a sharp image. (insert an image of Aperture image)
  

• Camera brightness/ aperture:
  The “Projector Brightness” slider in the software should be set to the maximum. It should only be reduced had a clean modulation is not possible in the following. Adjust the mechanical aperture. Consider only those areas in the camera image which show the regular waves. The displayed intensity curves (red) must be sinusoidal and may neither be undersaturated nor oversaturated. i.e. the red sine curve should be cropped at the blue lines. Note: if the curves are strongly flattened in the dark area without being close to the lower blue lines, the ambient light may be too strong. In this case darken the room. The Aperture dial on the camera has a scale f-stop from 16 to 1.4). Even for very bright condition (small objects), please avoid setting f-stop higher than 16. Otherwise the sharpness could be lost. If necessary, better reduce the value “Projector Brightness” in the software.

•  Fasten
  Lock down the camera and project’s position by fastening all screws including projector, camera and camera slide. The camera lens dials can be fixed with their locking screws.focus. This will not reduce the scan quality.  (insert an image of the camera dial lock)

Calibration

To Calibrate the Scanner

1. Set up the calibration corner
   Carefully fix the glass calibration panels in a 90 degree angle with two fixing brackets. Handle with care. (insert an image of the calibration panel)
2. Choose Calibration Pattern
   Choose a pattern size best fit the scanned object. The pattern should be slightly larger than the object/region to be scanned. For object sizes above ca.200mm, use the large 240 mm pattern on the back. Note: for starters, the pattern should be folded inwards. Advanced users can avoid undersired reflections with an outwardly folded pattern if necessary.
   
   
3. Remove the object and set up the glass calibration panels and the scanner in front of each other, about the same distance as the object previously so that the projection and camera image are sharp. The camera image should show the projected pattern as large as possible. In addition, the 6-rings and several other points of the calibration pattern must be visible. The entire camera image should be filled with about 15 to 70 markers.
4. Depending on the size of the projection, enter the correct scale length in the “scale[mm]”.
   
5. Check the camera image
   In the areas where the waves are visible, the red intensity curves must not reach the blue lines. If the object to be scanned is considerably darker than the white glass calibration panels, the sin waves will now be overdriven.  Work with the “Projector Brightness” slider in the software to adjust the red waves.
6. Click “Calibrate” to calibrate the entire scanner.