Ray Directions - Randomly according to intensity distribution

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Randomly According to Intensity Distribution

Page Contents

Description

Navigation

Controls

Application Notes

•Reading data from file

Related Topics

Description

The Randomly According to Intensity Distribution option generates ray directions based on a set of weighting factors in polar and azimuthal coordinates such that more rays are generated in the directions of large weighting factors. This ray direction specification is the default for sources created from IES files.

Navigation

This feature can be accessed by selecting Randomly according to intensity distribution as the ray direction type on the Positions/Directions tab of a detailed source dialog box.

Controls

Control	Inputs / Description	Defaults
Num Directions	Number of random ray directions per position	1
Parameters
Polar X, Y, Z	Direction vector of the polar axis in the apodization table.	0, 0, 1
Azimuth X, Y, Z	Direction vector of the azimuth angle in the apodization table.	1, 0, 0
Polar Angles(deg) – down Azimuth angles(deg) - across	The ray directions intensity table is organized such that column headers indicate Azimuth angles and row headers indicate Polar angles. The scale factors are then entered for each Polar-Azimuth angle pair.	0

OK	Accept settings and close the dialog box.
Cancel	Discard settings and close the dialog box.
Apply	Apply settings and keep the dialog box open.
Help	Access this Help page.

Application Notes

Reading data from file

By right clicking in the spreadsheet area the options "Interpolate from source FGD file" and "Replace With Data From a File" are available.

Interpolate from FGD file

Intensity data that has previously been calculated by FRED and saved to a *.fgd file can be used as the intensity data for generating ray directions. This can be useful, for example, when the source is described over a full hemisphere but only a portion of that space is desired to be used for ray generation. In such a scenario, the procedure would look like the following:

1.		The source, defined over the full hemisphere, is created.
2.		A Directional Analysis Entity is created that subtends only the angular range of interest.
3.		The rays are created (not raytraced) and an Intensity to Polar Grid analysis is performed and stored in an ARN.
4.		The ARN is saved to an FGD file.
5.		A new source is created using the same properties as the "full" source, except that the Random According to Intensity Distribution option is used and the FGD file from step 4 is applied.
6.		The source power is adjusted according to the total power reported by the analysis from step 3.

Replace With Data From a File

A properly formatted text file can also be used to load intensity data into the ray directions specification. The image below shows a properly formatted text file and the resulting specification as it appears in the dialog.

Two header lines are required at the beginning of the text file:

type intensity_on_polar_grid

format xyz_xyz_a

The third and fourth lines in the file are x,y,z vector components which indicate the directions of the polar and azimuthal axes, respectively. In the example file below, the polar axis is given by vector (0,0,1) and the azimuthal axis is given by vector (0,1,0).

The fifth line of the file consists of a placeholder 0 value followed by the azimuthal angles to which the data correspond. In this case, the azimuthal angles are -180, -90, 0, and 90 degrees.

The remaining rows consist of a polar angle value followed by intensity values at each spherical-polar coordinate. In this example the polar angles are 0, 2.5 and 5 degrees.