15.5.413 orientation

orientation, data, widths [, orientation, values, wavenumbers, grid, aspect, order, /vocal, /getj]

Determines local orientation in 2D or 3D data employing a method based on local Fourier Transforms.

data

The 2D or 3D array in which orientations are to be determined.

widths

must be a 2 or 3-element vector containing the FWHM of the Gaussian smoothing kernels applied in the dimensions (0 means no smoothing).

grid

is a 2 or 3-element vector containing the desired dimensions of the results. If it is not specified, then the results will have the same dimensions as data.

aspect

specifies the dimensions of a pixel, if they do not have an aspect ratio of 1.

order

contains the approximation order of the calculations, a number between 1 and 4 (default, most accurate).

orientation

The found orientation is returned in this argument (if specified), unless /getj is specified. The orientation is expressed in the 2d case as an angle in radians measured counterclockwise from the positive x-axis, and in the 3D case as a 2-element vector containing the x and y coordinates of the orientation vector relative to a unit z coordinate.

values

The found eigenvalues (measures for the data gradients in the principal directions) are returned in this argument (if specified), unless /getj is specified. The eigenvalues are returned in descending order.

wavenumber

By default, the determined local wavenumber in the direction of the found orientation is returned in this argument (if specified), unless /getj is specified. If /perpendicular is specified, then – for two-dimensional data only – the local wavenumber in the direction perpendicular to the found orientation is returned instead. The wavenumber is measured in units of one data element. A data set with values equal to sin(x) returns a wavenumber of 1 for the perpendicular wavenumber, and 0 for the parallel wavenumber. If a random data set is smoothed over FWHM w in one direction, then the parallel local wavenumber is on average equal to about 1.65/w.

/getj

If specified, then the unique elements of the inertia tensor are returned in values (the diagonal elements) and orientation (the off-diagonal elements), and the local power in wavenumber. This keyword is supplied for debugging purposes and may be withdrawn in the future.

/vocal

Induces periodical display of the progress status.

The returned orientations are ambiguous over 180 degrees.