Occultation Filter
Occultation Filter
Description Performs ray-tracing to simulate occultations.
Threaded Yes
Memory Usage Heavy
Stream Support Yes
Added In 0.3.0
Table of Contents


As the name suggests, this filter simulates occultations. It casts light rays from various points and counts how many of them pass through the particles. It is closely related to the Photometry Filter, but is a fair bit simpler because it needs fewer options.

There are two settings tabs for the Occultation Filter in addition to the standard three for sources, output, and label. These are Basic, and Bounds.


The Basic tab contains the settings that are going to be required for all uses of this filter. It is shown in the figure below. You can enter formulas for the position and size of each of the spheres. You can also enter the maximum number of wraps to perform on bounds as well as how many photons to use for each direction and the ranges and bin counts for the theta and phi angles. Note that theta=0 is out the x-axis and phi=0 is in the xy-plane.



The bounds options allow you to put in boundaries that photons hit and get moved to other locations. There are currently four types of boundaries. The first is a periodic cube. This boundary includes an option to simply use the bounds of the geometry. If this is selected, the other options are ignored. Otherwise you specify the minimum and maximum values for x, y, and z. The sliding brick option is useful for ring particles. The general plane allows you to specify a plane in space and an offset that the photon should be moved when it hits that plane. The periodic sphere will determine when a photon hits one edge and then move the photon to the opposite edge across the center of the sphere. None of the current bounds alter the direction of the photon.


The output stream from this filter can be sent to a plot with a Rectangular Surface Plot to produce an image of the light intensity getting through at each incoming angle. The transmitted intensity is v[2]. To get optical depth, use -log(v[2]).

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