ExtinctionProps1

This demo shows how to model a variety of volumes (using the built-in primitive geometry) with unique spectral extinction properties and temperature. Primitive volumes are handled a bit differently than RegularGrid objects in that overlapping primitives do not "sum" in term of the concentration of medium materials. Instead, primitive define distinct regions in which the volume itself matches that primitive’s definition exclusively.

The following demos, manuals and tutorials can provide additional information about the topics at the focus of this demo:

The focus of this demo is the configuration of materials that have volume extinction (absorption) properties (scattering properties can be modeled as well but, due to radiometry complexities, are handled in plugins). While DIRSIG4 allowed these types of volumes to have arbitrary reflectance properties to be co-defined, DIRSIG5 has specific ways to handle reflective/ transmissive interfaces between two media. These absorbing primitive volumes are primarily intended for testing and setting up simple extinction along a path.

The scene is composed of a flat background with a series of sphere, box and cylinder objects placed on and above it. The objects use the built-in geometry options primitives available in the GLIST file (there is no externally defined meshes or objects).

The geometry is defined in the file geometry/demo.glist and the materials in materials/demo.mat. All the materials in this scene use the Simple radiometry solver (arbitrarily chosen since this is a DIRSIG5-only demo), but the material optical properties vary.

The top row of objects contains two adjacent floating boxes that are defined with spectrally constant absorption. One is defined as a "surface" material with backing extinction and the second is defined as a "bulk" material with an absorption (they are both equivalent). To distinguish the surface material from materials that use extinction for a virtual thickness, a "volume_boundary" flag is used in the glist. The box defined with bulk properties needs to set a concentration that is applied to the given absorption inputs (they are treated as "specific" coefficients) and also the temperature. The temperature of the surface material is defined in the material. There is a set of "baffle" boxs around the two emitting volumes to help with the dynamic range of the image.

The two spheres are modeled with different absorption properties in the manner of the boxes, but without emission. There is a small sphere in the center of each, one diffuse and one specular, for visualization. Finally, there are two cylinders demonstrating embedding lower concentration medium inside a higher one.

The default convergence criteria for DIRSIG5 are not sufficient for this setup due to the noise from sampling an extended source randomly and the number of surfaces encountered.