1 / 22

The Radiosity Method

The Radiosity Method. Donald Fong February 10, 2004. Why?. Ray tracing has a visual signature Only models perfect specular reflection and transmission Interaction between diffusely reflecting surfaces Interiors, matte surfaces, indirect lighting. Basic idea.

paulaz
Download Presentation

The Radiosity Method

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The RadiosityMethod Donald Fong February 10, 2004

  2. Why? • Ray tracing has a visual signature • Only models perfect specular reflection and transmission • Interaction between diffusely reflecting surfaces • Interiors, matte surfaces, indirect lighting

  3. Basic idea • Divide surfaces into discrete patches • Object space algorithm • Model light transfer between patches as system of linear equations • Solve matrix equation for radiosity of each patch • Do it for R,G,B • Render patches as colored polygons

  4. Simplifying assumptions • All surfaces are perfectly diffuse • Does not matter which way light enters or leaves a surface • Radiosity is constant over a patch

  5. Radiosity Equation • Bi is radiosity of patch i • energy per unit area leaving a surface patch per unit time • rate energy emitted + rate energy reflected • Ei is non-zero for emitters • Riis reflectivity of the patch • Wavelength dependent • Fij is the form factor – how much light patch j contributes to patch i • Depends on geometric relationship – distance and relative orientation

  6. Radiosity solution • Finding form factors • Hemicube method • Meshing strategies • Solving set of linear equations to get radiosity for each patch

  7. Form factor example • Almost 100%

  8. Hemicube method • Efficient • Fq can be precomputed • Approximate • Aliasing

  9. Gauss-Siedel method • Iterative • Generates sequence of vectors that converges to the solution • Slow

  10. Gathering vs. Shooting • Gathering • One iteration updates a single patch by gathering contributions from all other patches • Shooting (and sorting) • Single iteration updates all receiving patches with unshot energy • Process patches according to amount of energy they are likely to radiate

  11. Progressive radiosity

  12. Another example

  13. Problems • Aliasing from hemicube method • Uniform pixel size • Using bilinear interpolation to reconstruct radiosity function • Using meshing of scene independent of variations in radiosity function

  14. Hemicube aliasing • Limited resolution of the hemicube pixels • Patches of same size map to different number of cells

  15. Reconstruction artifacts

  16. Meshing artifacts • Shadow leakage • Light leakage

  17. Meshing strategies • Discontinuity meshing • Completed before radiosity solution • Predict where discontinuities will occur • Adaptive meshing • Refine a “start” mesh as the solution progresses

  18. Discontinuity meshing • Mesh around expected discontinuities • Sharp boundaries from point light source or object contact • Derivative discontinuities from area light sources and multi-object shadows

  19. Hierarchical radiosity • Use different resolution depending on who is emitting and who is receiving

  20. Remeshing example

  21. Summary • Diffuse only • Costly to add specular • Not efficient • Meshing • Memory intensive

  22. Two pass solution

More Related