Allow transformed groups to be flattened

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 - Autograd support for local field projections using `FieldProjectionKSpaceMonitor`.
+- Function `components.geometry.utils.flatten_groups` now also flattens transformed groups when requested.
 
 ### Fixed
 - Regression in local field projection leading to incorrect results for `far_field_approx=True`.

tests/test_components/test_geometry.py

@@ -524,6 +524,33 @@ def test_flattening():
         for g in flat
     )
 
+    t0 = np.array([[2, 0, 0, 0], [3, 2, 0, 0], [1, 0, 2, 0], [0, 0, 0, 1.0]])
+    g0 = td.Sphere(radius=1)
+    t1 = np.array([[2, 0, 5, 0], [0, 1, 0, 0], [-1, 0, 1, 0], [0, 0, 0, 1.0]])
+    g1 = td.Box(size=(1, 2, 3))
+    flat = list(
+        flatten_groups(
+            td.Transformed(
+                transform=t0,
+                geometry=td.ClipOperation(
+                    operation="union",
+                    geometry_a=g0,
+                    geometry_b=td.Transformed(transform=t1, geometry=g1),
+                ),
+            ),
+            flatten_transformed=True,
+        )
+    )
+    assert len(flat) == 2
+
+    assert isinstance(flat[0], td.Transformed)
+    assert flat[0].geometry == g0
+    assert np.allclose(flat[0].transform, t0)
+
+    assert isinstance(flat[1], td.Transformed)
+    assert flat[1].geometry == g1
+    assert np.allclose(flat[1].transform, t0 @ t1)
+
 
 def test_geometry_traversal():
     geometries = list(traverse_geometries(td.Box(size=(1, 1, 1))))

tidy3d/components/geometry/utils.py

@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 from math import isclose
-from typing import Tuple, Union
+from typing import Optional, Tuple, Union
 
 import numpy as np
 
@@ -24,17 +24,25 @@
 ]
 
 
-def flatten_groups(*geometries: GeometryType, flatten_nonunion_type: bool = False) -> GeometryType:
+def flatten_groups(
+    *geometries: GeometryType,
+    flatten_nonunion_type: bool = False,
+    flatten_transformed: bool = False,
+    transform: Optional[MatrixReal4x4] = None,
+) -> GeometryType:
     """Iterates over all geometries, flattening groups and unions.
 
     Parameters
     ----------
     *geometries : GeometryType
         Geometries to flatten.
-
     flatten_nonunion_type : bool = False
         If ``False``, only flatten geometry unions (and ``GeometryGroup``). If ``True``, flatten
         all clip operations.
+    flatten_transformed : bool = False
+        If ``True``, ``Transformed`` groups are flattened into individual transformed geometries.
+    transform : Optional[MatrixReal4x4]
+        Accumulated transform from parents. Only used when ``flatten_transformed`` is ``True``.
 
     Yields
     ------
@@ -44,7 +52,10 @@ def flatten_groups(*geometries: GeometryType, flatten_nonunion_type: bool = Fals
     for geometry in geometries:
         if isinstance(geometry, base.GeometryGroup):
             yield from flatten_groups(
-                *geometry.geometries, flatten_nonunion_type=flatten_nonunion_type
+                *geometry.geometries,
+                flatten_nonunion_type=flatten_nonunion_type,
+                flatten_transformed=flatten_transformed,
+                transform=transform,
             )
         elif isinstance(geometry, base.ClipOperation) and (
             flatten_nonunion_type or geometry.operation == "union"
@@ -53,7 +64,21 @@ def flatten_groups(*geometries: GeometryType, flatten_nonunion_type: bool = Fals
                 geometry.geometry_a,
                 geometry.geometry_b,
                 flatten_nonunion_type=flatten_nonunion_type,
+                flatten_transformed=flatten_transformed,
+                transform=transform,
+            )
+        elif flatten_transformed and isinstance(geometry, base.Transformed):
+            new_transform = geometry.transform
+            if transform is not None:
+                new_transform = np.matmul(transform, new_transform)
+            yield from flatten_groups(
+                geometry.geometry,
+                flatten_nonunion_type=flatten_nonunion_type,
+                flatten_transformed=flatten_transformed,
+                transform=new_transform,
             )
+        elif flatten_transformed and transform is not None:
+            yield base.Transformed(geometry=geometry, transform=transform)
         else:
             yield geometry
 

tidy3d/components/scene.py

@@ -116,7 +116,7 @@ def _validate_num_geometries(cls, val):
             return val
 
         for i, structure in enumerate(val):
-            for geometry in flatten_groups(structure.geometry):
+            for geometry in flatten_groups(structure.geometry, flatten_transformed=True):
                 count = sum(
                     1
                     for g in traverse_geometries(geometry)