From 7bfd25e57e251f2d3e316722be7eba60f0d3094d Mon Sep 17 00:00:00 2001
From: Qiming <qiming@flexcompute.com>
Date: Thu, 12 Sep 2024 17:31:22 -0400
Subject: [PATCH] Fixed wrong projection monitor error for out-of-domain
 structures

---
 CHANGELOG.md                             |  3 ++
 tests/test_components/test_simulation.py | 32 +++++++++++++++
 tidy3d/components/simulation.py          | 52 +++++++++++++++++++++++-
 3 files changed, 86 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index bce65683f..c0a30f2f7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- Stopped raising error when field projection monitor intersecting structures outside of the simulation domain.
+
 ## [2.7.3] - 2024-09-12
 
 ### Added
diff --git a/tests/test_components/test_simulation.py b/tests/test_components/test_simulation.py
index b68dea733..8b194074b 100644
--- a/tests/test_components/test_simulation.py
+++ b/tests/test_components/test_simulation.py
@@ -2977,3 +2977,35 @@ def test_validate_sources_monitors_in_bounds():
             grid_spec=td.GridSpec(wavelength=1.0),
             monitors=[mode_monitor],
         )
+
+
+def test_2d_projection_monitor_out_sim_domain():
+    # set up a structure interset with far field monitor outside the computational domain
+    cylinder = td.Structure(
+        geometry=td.Cylinder(axis=2, radius=0.5, length=2), medium=td.PECMedium()
+    )
+
+    num_phi = 100
+    theta = np.pi / 2
+    phis = np.linspace(0, np.pi, num_phi)
+    monitor_far = td.FieldProjectionAngleMonitor(
+        size=[2, 2, 0.5],
+        freqs=[1e12],
+        name="far_field",
+        theta=theta,
+        phi=phis,
+    )
+
+    sim2d = td.Simulation(
+        size=(4, 4, 0),
+        run_time=1e-12,
+        grid_spec=td.GridSpec.uniform(dl=0.025),
+        sources=[],
+        structures=[cylinder],
+        monitors=[monitor_far],
+        boundary_spec=td.BoundarySpec(
+            x=td.Boundary.pml(),
+            y=td.Boundary.pml(),
+            z=td.Boundary.periodic(),
+        ),
+    )
diff --git a/tidy3d/components/simulation.py b/tidy3d/components/simulation.py
index b64c3f26e..1086920f8 100644
--- a/tidy3d/components/simulation.py
+++ b/tidy3d/components/simulation.py
@@ -136,6 +136,12 @@
 # height of the PML plotting boxes along any dimensions where sim.size[dim] == 0
 PML_HEIGHT_FOR_0_DIMS = inf
 
+# fraction of structure size to monitor along 0 dim in 2D simulations
+FRACTION = 0.9
+
+# Minimum size of monitor
+MIN_MONITOR_SIZE = 1e-12
+
 
 class AbstractYeeGridSimulation(AbstractSimulation, ABC):
     """
@@ -2756,7 +2762,51 @@ def _projection_monitors_homogeneous(cls, val, values):
         with log as consolidated_logger:
             for monitor_ind, monitor in enumerate(val):
                 if isinstance(monitor, (AbstractFieldProjectionMonitor, DiffractionMonitor)):
-                    mediums = Scene.intersecting_media(monitor, total_structures)
+                    if monitor.volume() != 0.0:
+                        if not (
+                            all(
+                                monitor_min >= sim_min
+                                for monitor_min, sim_min in zip(
+                                    monitor.bounds[0], structure_bg.geometry.bounds[0]
+                                )
+                            )
+                            and all(
+                                monitor_max <= sim_max
+                                for monitor_max, sim_max in zip(
+                                    monitor.bounds[1], structure_bg.geometry.bounds[1]
+                                )
+                            )
+                        ):
+                            exclude_surfaces = []
+                            dimensions = ["x", "y", "z"]
+                            for i, dim in enumerate(dimensions):
+                                if monitor.bounds[0][i] <= structure_bg.geometry.bounds[0][i]:
+                                    exclude_surfaces.append(f"{dim}-")
+                                if monitor.bounds[1][i] >= structure_bg.geometry.bounds[1][i]:
+                                    exclude_surfaces.append(f"{dim}+")
+                            new_min = np.maximum(monitor.bounds[0], structure_bg.geometry.bounds[0])
+                            new_max = np.minimum(monitor.bounds[1], structure_bg.geometry.bounds[1])
+                            new_size = tuple(new_max - new_min)
+                            # Add a minimum value to the monitor along 0-dim in 2D simulations
+                            new_size = tuple(
+                                MIN_MONITOR_SIZE if num == 0 else num for num in new_size
+                            )
+                            new_center = tuple((new_max + new_min) / 2)
+                            monitor_test = monitor.updated_copy(center=new_center, size=new_size)
+                            monitor_dict = monitor_test.dict()
+                            # Append exclude surfaces for 2D simulation to existing ones
+                            existing_exclude_surfaces = monitor_dict.get("exclude_surfaces") or []
+                            updated_exclude_surfaces = list(
+                                set(existing_exclude_surfaces + exclude_surfaces)
+                            )
+                            monitor_dict["exclude_surfaces"] = updated_exclude_surfaces
+                            surfaces = monitor_test.surfaces_with_exclusion(**monitor_dict)
+                            mediums = set()
+                            for surface in surfaces:
+                                _mediums = Scene.intersecting_media(surface, total_structures)
+                                mediums.update(_mediums)
+                    else:
+                        mediums = Scene.intersecting_media(monitor, total_structures)
                     # make sure there is no more than one medium in the returned list
                     if len(mediums) > 1:
                         raise SetupError(