add remaining high value features

backend/nodes/surface_common.py

@@ -0,0 +1,22 @@
+from __future__ import annotations
+
+from backend.data_types import DataField
+
+
+_LENGTH_UNITS = {"m", "km", "cm", "mm", "um", "µm", "nm", "pm", "fm"}
+
+
+def unit_dimension_key(unit: str) -> str:
+    text = str(unit or "").strip().replace("µ", "u")
+    if not text:
+        return ""
+    if text in _LENGTH_UNITS:
+        return "length"
+    return text
+
+
+def require_compatible_xy_z_units(field: DataField, node_name: str) -> None:
+    xy_key = unit_dimension_key(field.si_unit_xy)
+    z_key = unit_dimension_key(field.si_unit_z)
+    if xy_key and z_key and xy_key != z_key:
+        raise ValueError(f"{node_name} requires compatible XY and Z units, matching Gwyddion's topography-only behavior.")