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 open. 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.
   

Scan Object Setup

Place the scan object in front of the projector. It takes about 8-10 scans to capture the object in full dimension. It is helpful to set your object to be scanned on a turntable (available in the shop) to ensure that the object is rotated about a single axis, which will be helpful later on during the align process. 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 redline/sine curves work)

 Image image image

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

• Working Distance 
  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 with highlights on scale mm)
   
   
2. Choose Calibration Pattern Size
   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.(Comparison of the three different scale, image image image)
   
   
3. Remove the object. Set up the glass calibration panels in front of the projector at the same location where the object was previously placed so that the projection and camera image on your monitor are sharp. The camera image should show the projected pattern as large as possible. The 6-rings and at least 24 points of the calibration pattern must be visible. The entire camera image should be filled with about 24 to 70 markers. (camera image of the projected pattern)
   
   
4. Depending on the size of the projection, enter the correct scale length in the “scale[mm]”.
   
   
   
5. Check the camera image
   The camera should not be able to see past the calibration panels. 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. (insert Camera image, also processing bar in the same image)
   
   
6. Click “Calibrate” to calibrate the scanner.  

   In this step the software will first measures the position, orientation, focal length and distortion coefficients of the camera. Then it will project a pattern sequence in order to determine the same optical properties of the projector. If Texturing is not switched off, it will also perform a white balance measurement.

   After a successful calibration, DAVID will project a checkerboard pattern, whose corner points should fall exactly onto the calibration markers.

Scan

1. After the calibration is successfully done, the scanner is ready to perform. Place the object back to its original position and remove the calibration panel. Make sure the working distance is as same as during setup and calibration. Do Not change the focus of camera or projector. NOTE: with a wrong working distance, the camera image and projected stripes would be blurred.
   
   
2. Before each scan, make sure the red sine curves are not cropped/overdriven in the ares where the wave pattern is visible. If adjustment is necessary, adjust the “Project Brightness” in the software.
   
   
3. Go to Structure Light panel, select, Pattern Parameters “quality, “Default” (recommended), or “Speed”
   
   
   
4. Click “Start” to scan the image. Once the scan is done, click “Add Scan to List of Scans for Shape Fusion” to save the scan to the “List of Scans”.
   
   
   
5. It takes 6-8 scans around the object and couple more from top and down to capture the model. Make sure to scan the object multiple times with different angles to get all aspects of it, Delete the ones with lower quality.
   In order for the scans to align properly later on, it is important to scan the object systematically. Make sure the views each scan overlaps with one another. Note: "Add to List" only stores the scan to the "List of Scans". It does NOT save the scans to your computer. If the program crashes during fusion or scanning process, all scans on the list will be lost.
   
   
6. When the scans are done. Make sure all qualified scans on "List of Scans" are saved to your local computer.