**Date:**
Wed 13 Mar

**Time:**
15.00

**Place:**
sala riunioni (terzo piano)

**Speaker:**
Marco Pellegrini (Ist. Mat. Comp. del CNR, Pisa)

**Title:**
Efficient algorithms for radiosity computations

**Reference:**
Leila de Floriani

**Abstract.**
The exchange of radiant energy (e.g., visible light in Graphics,
or infra-red radiation in Heat Transfer Engineering) in simple
models is approximated by the solution of a system of linear
"energy transport" equations. Each variable in such a system
represents the total energy emitted by a discrete surface element,
and the coefficients depend on the "form factors" between pairs of
surface elements. A form factor is the fraction of energy leaving
one element which directly reaches the other. This depends only on
the geometry of the physical model. Determining good approximations
of form factors is the most time-consuming step in these methods,
when the geometry of the model is complex due to occlusions.
In this talk we introduce a new characterization of form factors
and develop a new asymptotically efficient Monte Carlo method for
simultaneously approximating all form factors in an *occluded*
polyhedral environment. This is the first algorithm for which an
asymptotic time bound *and* a bound on the absolute approximation
error has been proved. For typical scenes, it is an order of
magnitude faster than methods based on the hemisphere paradigm.

Note: the first 30 minutes of the talk consist of a survey.