Log-Polar PSDF
Compute the power spectral density function in log-polar coordinates. The x-axis is the azimuthal angle (0-360 degrees) and the y-axis is log(frequency). Better than Cartesian PSDF for anisotropy analysis. Equivalent to Gwyddion's psdf_logphi.c module.
Inputs
| Name |
Type |
Required |
Description |
| field |
DATA_FIELD |
Yes |
Input spatial-domain field |
Outputs
| Name |
Type |
Description |
| psdf |
DATA_FIELD |
Power spectral density in log-polar coordinates (domain=frequency) |
Controls
| Name |
Type |
Default |
Description |
| n_phi |
INT |
180 |
Number of azimuthal angle bins (36–720) |
| n_r |
INT |
100 |
Number of radial (log-frequency) bins (20–500) |
Notes
- The mean value is subtracted before computing the 2D FFT, and the power spectrum is shifted so DC is at the centre.
- Bilinear interpolation is used when sampling the Cartesian power spectrum onto the log-polar grid.
- The output is log-scaled via
log1p for better visual contrast.
- Output xreal is 360.0 (degrees) and yreal is log(r_max) where r_max is half the shorter image dimension.
- Anisotropic surfaces produce bright bands at specific azimuthal angles; isotropic surfaces appear uniform along the angle axis.
