adding more nodes

docs/nodes/Facet Analysis.md

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+# Facet Analysis
+
+Compute the facet orientation distribution of a surface. Outputs a 2D histogram (stereographic projection) where the x-axis is the azimuthal angle and y-axis is the inclination. Equivalent to Gwyddion's facet_analysis.c module.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Input surface |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| facet_map | DATA_FIELD | 2D histogram of facet orientations (phi vs theta) |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| n_bins | INT | 180 | Number of azimuthal bins; theta bins = n_bins/4 (30–720) |
+| kernel_size | INT | 3 | Sobel gradient kernel size in pixels (3–9, odd) |
+
+## Notes
+
+- The output is a normalised probability density — it sums to 1.0.
+- X-axis: azimuthal angle phi (0–360°). Y-axis: inclination theta (0° = flat, max = steepest facet).
+- A flat surface produces a single bright spot near theta=0. A surface with distinct facets shows multiple peaks.
+- Larger kernel_size smooths the gradient estimate, reducing noise sensitivity.