# Table of Contents

1. Welcome to DAVID (help_welcome.htm)
2. Camera Calibration (help_camera_calibration.htm)
3. 3D Laser Scanning (help_3d_scanning.htm)
4. Shape Fusion (help_shape_fusion.htm)
5. Frequently Asked Questions (help_faq.htm)
6. General Hints (help_hints.htm)

# Shape Fusion

DAVID-Shapefusion allows a convenient alignment and combination of 3D scans from different viewing directions. It is more than just an ordinary stitching tool, since it combines

- an easy-to-use user-driven outlier removal,
- an automatic and semi-automatic surface registration,
- and a noise reducing surface fusion method, which is very robust against outliers.

The result is a smoothed 360 degree triangle mesh of your 3D model.

The following steps will guide you through the shape fusion dialog of DAVID:

1. First of all you must add one or more scans of your model to the input list by clicking the "Add..." button:
2. If DAVID detects more than one single surface segment in your scan, a 'Surface Filter' dialog window appears:
   By moving the slider of the dialog from left to right you can choose which segments will be removed an which will be retained. The 3D window shows a preview of the result. Segments that will be removed are shown in red, segments that will be retained are shown in green:
   (The same dialog will appear again when you save your fusion result.)
3. After adding all your scans to the input list, press the 'Arrange' button to arrange them side by side:
4. The next step is the alignment of your scans.
   Press the 'Align' button to open the 'Registration Dialog' window of DAVID-Shapefusion:
   Here you can choose between six different registration modes for pairwise surface alignment:
   'Free rotation', 'Rotation around x-axis', 'Rotation around y-axis', 'Rotation around z-axis', 'Manual alignment', and 'Only fine registration'. Using the first 'Free rotation' mode, the computer performs a coarse registration between two scans at a time, without any constraints regarding rotation or translation. More precisely, the software searches for the relative pose between two scans that provides the largest contact area. This unconstrained contact area maximization works in many cases, but not in every case. The next three registration modes are quite similar to the first one, except that the relative pose between two scans is constrained. For example the 'Rotation around y-axis' mode assumes that your object was rotated around the y-axis of the reference coordinate system (the y-axis is the upright axis if you used DAVID for scanning) and furthermore assumes that the object was not translated along the y-axis. But the center of rotation remains unconstrained, which means that you don't have to use a turn-table, just rotate your object manually. After you have chosen the registration mode, the registration dialog will guide you through the alignment process.
5. In the case of our Beethoven bust, we have rotated the bust around the y-axis and therefore we choose the 'Rotation around y-axis' mode.
6. Now step 1 instructs to click on the scan that we want to align. After clicking on that scan in the 3D window, you will see a red bounding box around the chosen scan:
7. Click on a second scan to which you want to attach the first one...
   Coarse registration will take place. After a few seconds both scans are aligned:
8. Just repeat the same procedure for the other scans. After that, you 3D model should look like this:
   Note that the surface alignment must be very precise in order to get an adequate result in the fusion process. A precise alignment is characterized by many surface penetration points (the color of the overlapping surfaces in the 3D window should flicker if you rotate the object).
9. If the registration process did not find a good alignment, just try it again. Since the method is based on an randomized algorithm, you have a good chance that it will work at the second or third time. If this doesn't help you can use the 'manual alignment' mode or you can manually align the scans in the 3D window and use the 'Only fine registration' mode. The 'manual alignment' mode allows you to specify corresponding point pairs, which should get in contact after alignment:
10. After you have aligned your scans precisely, the mesh fusion can take place. Just press the 'Fuse' button and you will see the result.
11. The result heavily depends on the fusion parameters called 'Resolution', 'Smoothness' and 'Removal'. We would therefore recommend to try different parameter settings. Start with a low resolution (e.g. 100) because at a low resolution the fusion process is much more robust against inaccurate alignments, noise and outliers. A higher resolution means a longer processing time and much more triangles. If your fusion result gets holey and untight at a higher resolution you have to increase the 'Smoothness' parameter. Again start with a small 'Smoothness' value and increase it step by step until the result is satisfactory.
12. Last but not least you can click on the 'Shrink' button for multiple times to reduce unclean borders.
13. The 'Save' button opens a new dialog window where you can choose between the *.OBJ and *.PLY file format. You can choose whether to save your fusion result or your aligned and filtered 3d scans.
    But the saving feature is not activated in the trial edition of DAVID-Shapefusion.

# Table of Contents

1. Welcome to DAVID (help_welcome.htm)
2. Camera Calibration (help_camera_calibration.htm)
3. 3D Laser Scanning (help_3d_scanning.htm)
4. Shape Fusion (help_shape_fusion.htm)
5. Frequently Asked Questions (help_faq.htm)
6. General Hints (help_hints.htm)