code structure:

0. basic data structures, and operations.

1. file io.

2. preprocessing.
    todo: muti-features

3. matched points.

4. initialization.
    todo: to be more robust.

5. optimization.
    todo: deform the depth.

6. warper.
    todo: the border of faces of skybox is empty.

7. stitching.
    todo: multi-band.

8. novel view content generation.
    todo: generate back layer rgbd content.

9. 3d viewer for the Panorama-type RGBD images.
    todo: standalone viewer toolkits.