adding more nodes

docs/nodes/Grain Cross.md

@@ -0,0 +1,33 @@
+# Grain Cross
+
+Correlate grain properties between two fields using a shared grain mask. Reports per-grain property pairs and the Pearson correlation coefficient. Equivalent to Gwyddion's grain_cross.c module.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field_a | DATA_FIELD | Yes | First height field |
+| field_b | DATA_FIELD | Yes | Second height field |
+| mask | IMAGE | Yes | Binary grain mask (white = grain) |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| correlation | RECORD_TABLE | Per-grain property pairs and Pearson correlation coefficient |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| property_a | dropdown | mean_height | Property to compute from field_a: area, mean_height, max_height, or volume |
+| property_b | dropdown | max_height | Property to compute from field_b: area, mean_height, max_height, or volume |
+| min_size | INT | 10 | Minimum grain area in pixels; smaller grains are excluded (1–100000) |
+
+## Notes
+
+- Grains are identified by connected-component labelling (`scipy.ndimage.label`) on the binary mask.
+- The **area** property uses physical pixel area (dx * dy). **Volume** integrates height above the mean of non-grain pixels.
+- Each table row contains one grain's property pair formatted as "value_a / value_b".
+- The final row reports the Pearson correlation coefficient r between the two property vectors (requires at least 2 grains).
+- Both fields must have the same pixel dimensions as the mask.