How to compute view factors between two surfaces

Given a geometry, how do I compute the view factors without using DO model?

For a given geometry, suppose, we have Surfaces 1, 2, ...

We want the view factor between 1 and 2: F12.

* Turn on Radiation->DO. You might want to increase accuracy by increasing the pixellization. Set the DO iteration frequency to 1.
* set the emissivity of all walls to 1.0
* Set the temperature of all walls to ZERO, with the exception for T1 which you can set to any number (300 will work).
* Under Solve->Controls->Limits, set the limit of Temperature to ZERO for its lower bound.
* Solve the problem to convergence.
* Get the radiation heat flux from Surface 2 with Solve->Reports->Radiation Heat flux. Call this Q2.
* Get the surface area of wall 1 using Surface integrals->Area. Call this A1.

F12 = Q2 / (sigma A1 T1^4)

Sigma = 5.67 e-8 W/(m^2 - K^4)

The following method gave me agreement to the analytical formula within 1 part in a thousand.

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