If semitransparent materials with finite values of the
absorption coefficient in some spectral bands are present in the
setup, the radiative heat transport in them will be described
by means of the ray tracing model. The model is activated by
switching on the ** Integrated
Intensity** procedure in the list of the **Physical
Phenomena** for the regions containing the
semitransparent materials.

The thermal computation begins then with geometrical tracing of rays which start in each node of the unstructured mesh inside of the region filled with the semitransparent material and at the region boundary. The number of required considered reflections and refractions at the region boundaries will be evaluated and the tracing of each particular ray from the ray bundle for the target node will be continued until the interruption criterion is achieved.

The found geometrical parts of the rays and other auxiliary information is stored and will be retrieved during the thermal computation with solution of the radiation transport equation in the semitransparent materials.

The preparatory geometrical ray tracing can be started also
without any thermal computation. Open the menu **
Computation ** and select the item **Start
Tracing Rays**. The geometrical ray tracing will be
done and all found rays will be stored ready for access during the
computation.