Calibration

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Projector Setup

Start by running DAVID3_x64 (from the desktop, taskbar, or Windows Start Menu).

The DAVID-LASERSCANNER interface window will open. On the left hand side:

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

Camera Setup

Remove camera lens cap (PLACE IN SLIDING DRAWER SO IT WON'T GET LOST)

Place the scan object in front of the projector.
Optionally place object on the turn table. It takes about 8-10 scans to capture the object in full dimension. It may be helpful to set your object to be scanned on a turntable (one is located in the lower area of scanning station) to ensure that the object is rotated about a single axis, which will be helpful later on during the align process.
You should now see your object covered with the projected pattern within the DavidScanner interface
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.

To achieve the best result, carefully adjust camera regarding the following considerations:

Working Distance

Adjust the working distance by moving the tripod or object on table to make sure the screen projected from the projector covers the entire object, not less, not much more either.

Working Distance is the distance between the object to be scanned and the projector.

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.

Camera Position

To adjust the location and angle of the camera, loosen the thumbscrew on the bottom of the camera to slide it. In general, the angle of the camera should be set to 22 degrees. 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 once the location is adjusted.

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 capturing the projection.

Camera Focus

Adjust the aperture of the camera so that you 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.

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. Use hand-force and do not over-tighten hardware.

Calibrate Scanner

To Calibrate the Scanner:

Set up the calibration corner
Carefully secure the glass calibration panels in a 90 degree angle with two fixing brackets. Handle with care.
Choose a Calibration Pattern Size
Choose a pattern size that best fits the object/region to be scanned; should be slightly larger than the object/region. For object sizes greater than 200mm across any one dimension, use the large 240 mm pattern on the back. Note: For beginners, the pattern should be folded inwards; advanced users can avoid undesired reflections with an outwardly-folded pattern, if necessary.
Remove the object from the scanning area. 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.
Depending on the size of the projection, enter the correct scale length in the “scale[mm]”.
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 sine waves will be overdriven. Work with the “Projector Brightness” slider in the software to adjust the red waves.
Click “Calibrate” to calibrate the scanner.
In this step the software will first measure 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 enabled, 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.