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Friday, May 17, 2013

Machine epsilon in Ray tracer

Because of inaccuracy of floating point calculation in computer system, ray-tracer could fail ray-intersection test. For instance, the calculated intersection point might lie below or above the actual surface. This problem makes self-intersection of secondary rays or overlap of geometries. In order to handle this problem appropriately, we usually add a small distance along the ray (rayepsilon in PBRT) or normal direction. However, it is also important to choose an epsilon value. H. Dammertz said that too small epsilon results i self-intersections of secondary rays, too large epsilon results in overlaps from the extended geometry.

Ray-tracing for transparent or translucent objects, it is important to trace rays not only the surface facing a camera, but also the surface hidden from the camera. Ray-tracer would fail to intersection test for the hidden surface which is very close to the surface which the rays already intersected. If we modeled the volume with some interfaces, outside will be air and inside will be a material. To check if the ray is within the volume, ray-intersection test will be important. When ray intersects the first surface, the ray will get into the volume. When the ray intersects the second surface, the ray will get out of the volume. When second surface is too close to the first surface, ray-tracer would fail to detect the intersection and regard the ray still within the volume, even though the ray already got out of the volume.

How do I handle this issue?


Monday, May 13, 2013

TELNET Starwars


Sunday, May 12, 2013

Useful torrent trackers

The pirate bay:

- Famous for large data and list

- Good ratio policy! It updates its ratio once a day, so I don't have to worry about ratio. In the middle of September 2009, the service is stopped suddenly. Demonoid posted that the site has a problem, so it is going to be recovered sooner or later.

- Dec 14, 2009, Demonoid is back!

- In Dec, 2010, it is moving to new place

- It's good for latest data and list.
- November 26, 2009, Mininova declared that they start limiting its activities to content distribution service. Therefore, large amount of data were gone. It means Mininova is no more useful!

- Torrent search engine. It has comprehensive information on many torrents tracker. But, I don't think it collects from every torrent tracker.

Eclipse productions:

- In this torrent, latest full metal alchemist can be found.

- In this torrent, most recent full metal alchemist can be found.

minglong BitTorrent Tracker:

- Tomodachi put its latest work on this tracker. Of course, most recent full metal alchemist can be found here.

Updated 2013/05/12


- Russian torrent tracker


Wednesday, May 1, 2013

Special effect for 3ds max and final cut

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