Free Halo Simulation Program

General Description

HaloPoint 2.0 traces light rays through ice crystals (hexagonal lattice, Ice Ih) according to the laws of geometric optics and produces a coloured scatter plot of the dots of light created by the rays that escape the crystals. The faces of the ice crystals are mathematically defined for the computer. At each face the light is split to reflected and refracted (transmitted) part, whose intensities are govenrned by Fresnel equations. The ray is followed until it leaves the crystal, and a dot is plotted to the celestial sphere opposite to the direction of that ray. A new ray is taken under consideration and the cycle is repeated for as many rays as wanted, even millions. This procedure is an application of the scientific calculation method known as Monte-Carlo -process, which is succesfully applied to a variety of tasks. HaloPoint 2.0 uses an algorithm very similar to those explained by Pattloch and Tränkle^[1], Tape^[2] and Cowley^[3].

Features

• In HaloPoint 2.0 ice crystal profiles (cross-sections) are not confined to merely symmetrical hexagons; for each of the six prism faces user can define a distance from the origin thus allowing one to create arbitrary cross sections, see here. Ice crystal samples and halo display analysis have shown that such modifications are needed.
• Pyramid crystals can be easily defined. The height and apex angle of the pyramid at both ends of the prism can be individually controlled, see here.
• In addition to the common crystal orientations (plate, column, random, Parry and Lowitz) one can specify arbitrary orientations.
• Each variable controlling crystal dimensions, shape and orientation can be set to vary according to uniform or normal distribution with a user defined interval / standard deviation.
• Simulations can be run with full colour spectrum, or using only user selected wavelengths. Black and white -simulations are also possible. The shade levels of the resulting halo points can be chosen between 1 and 256.
• The field of view and persepective projection of the simulation can be made to match a photograph by choosing the lens focal length, sensor/film size and centerpoint of the image in the sky, see here.
• Multiple scattering halo phenomena can be simulated with HaloPoint 2.0, see here.
• HaloPoint 2.0 offers numerous ways to perform ray path filtering in simulations, thus permitting examination of halo forms separately without overcluttering the screen with uninteresting halo points. See example of the user interface for setting filtering conditions here.
• With haloPoint 2.0 series of simulations can be run. Just set up a list of simulation runs you want to carry out and leave the computer to do the task. See example of the user interface for setting up a simulation series here.
• With HaloPoint 2.0 it is possible to draw an image of a raypath through the crystal for each point in the simulation. The crystal+raypath -image can be viewed from any given direction in Raypath Visualization -window.
• Raypaths of a simulation can be sorted and examined afterwards extensively.

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:: Copyright © 2010 by Jukka Ruoskanen ::