adding more nodes

docs/nodes/Log-Polar PSDF.md

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+# 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.