diff --git a/src/bonsai/bonsai/bim/module/alignment/data.py b/src/bonsai/bonsai/bim/module/alignment/data.py
new file mode 100644
index 0000000000..a4dc5f18ed
--- /dev/null
+++ b/src/bonsai/bonsai/bim/module/alignment/data.py
@@ -0,0 +1,75 @@
+# ==============================================================================
+# Saikei Civil - Civil Engineering Tools for Blender
+# Copyright (c) 2025 Michael Yoder / Desert Springs Civil Engineering PLLC
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
+#
+# Primary Author: Michael Yoder
+# Company: Desert Springs Civil Engineering PLLC
+# ==============================================================================
+
+
+"""Data caching layer for the alignment module
+
+This module provides cached access to alignment data for UI display,
+following Bonsai's data loading pattern.
+"""
+
+
+def get_ifc_file():
+    """Get the current IFC file from Bonsai"""
+    try:
+        import bonsai.tool as tool
+
+        return tool.Ifc.get()
+    except (ImportError, AttributeError):
+        return None
+
+
+class AlignmentData:
+    """Cached alignment data for UI display"""
+
+    data = {}
+    is_loaded = False
+
+    @classmethod
+    def load(cls):
+        """Load alignment data from IFC file"""
+        cls.data = {
+            "alignments": [],
+            "active_alignment": None,
+            "segments": [],
+        }
+
+        ifc = get_ifc_file()
+        if ifc is None:
+            cls.is_loaded = True
+            return
+
+        # Load all alignments
+        alignments = ifc.by_type("IfcAlignment")
+        cls.data["alignments"] = [
+            {
+                "id": a.id(),
+                "name": a.Name or f"Alignment {a.id()}",
+                "global_id": a.GlobalId,
+            }
+            for a in alignments
+        ]
+
+        cls.is_loaded = True
+
+    @classmethod
+    def refresh(cls):
+        """Force refresh of alignment data"""
+        cls.is_loaded = False
+        cls.load()
diff --git a/src/bonsai/bonsai/bim/module/alignment/prop.py b/src/bonsai/bonsai/bim/module/alignment/prop.py
new file mode 100644
index 0000000000..e4f67b4169
--- /dev/null
+++ b/src/bonsai/bonsai/bim/module/alignment/prop.py
@@ -0,0 +1,258 @@
+# ==============================================================================
+# Saikei Civil - Civil Engineering Tools for Blender
+# Copyright (c) 2025 Michael Yoder / Desert Springs Civil Engineering PLLC
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
+#
+# Primary Author: Michael Yoder
+# Company: Desert Springs Civil Engineering PLLC
+# ==============================================================================
+
+
+"""Property groups for the alignment module"""
+
+import bpy
+from bpy.types import PropertyGroup
+from bpy.props import (
+    StringProperty,
+    FloatProperty,
+    IntProperty,
+    BoolProperty,
+    CollectionProperty,
+    EnumProperty,
+)
+
+
+def get_pi_type_items(self, context):
+    """Get available PI types based on position in list"""
+    # First and last PIs are always endpoints (no curve)
+    # Interior PIs can have curves
+    return [
+        ("ENDPOINT", "Endpoint", "Start or end point (no curve)"),
+        ("TANGENT", "Tangent", "Pass-through point (no curve)"),
+        ("CURVE", "Curve", "Point of intersection with curve"),
+    ]
+
+
+def _on_radius_update(self, context):
+    """Callback when radius property changes.
+
+    This dynamically imports the operator module to call on_radius_changed,
+    avoiding circular imports since prop.py is imported before operator.py.
+    """
+    from . import operator as ops
+
+    ops.on_radius_changed(self, context)
+
+
+class AlignmentPI(PropertyGroup):
+    """Property group for a single PI (Point of Intersection)
+
+    In the PI method, alignments are defined by:
+    - Endpoint PIs: Start (POB) and End (POE) points
+    - Interior PIs: Points where tangents intersect, optionally with curves
+    """
+
+    # Coordinates
+    x: FloatProperty(
+        name="X",
+        description="X coordinate (Easting)",
+        default=0.0,
+        precision=3,
+        unit="LENGTH",
+    )
+
+    y: FloatProperty(
+        name="Y",
+        description="Y coordinate (Northing)",
+        default=0.0,
+        precision=3,
+        unit="LENGTH",
+    )
+
+    # PI Type
+    pi_type: EnumProperty(
+        name="Type",
+        description="Type of PI point",
+        items=[
+            ("ENDPOINT", "Endpoint", "Start or end point (no curve)"),
+            ("TANGENT", "Tangent", "Pass-through point (no curve)"),
+            ("CURVE", "Curve", "Point of intersection with curve"),
+        ],
+        default="TANGENT",
+    )
+
+    # Curve parameters (only used when pi_type == "CURVE")
+    radius: FloatProperty(
+        name="Radius",
+        description="Curve radius (0 = no curve, sharp angle)",
+        default=0.0,
+        min=0.0,
+        precision=3,
+        unit="LENGTH",
+        update=_on_radius_update,
+    )
+
+    # Computed/display values (updated by recalculate operator)
+    length_to_next: FloatProperty(
+        name="Length",
+        description="Length of tangent to next PI",
+        default=0.0,
+        precision=3,
+        unit="LENGTH",
+    )
+
+    direction_to_next: FloatProperty(
+        name="Direction",
+        description="Bearing/direction to next PI (degrees)",
+        default=0.0,
+        precision=4,
+        subtype="ANGLE",
+    )
+
+    # Station at this PI (computed)
+    station: FloatProperty(
+        name="Station",
+        description="Station value at this PI",
+        default=0.0,
+        precision=2,
+    )
+
+    # Selection state
+    is_selected: BoolProperty(
+        name="Selected",
+        description="Whether this PI is selected for editing",
+        default=False,
+    )
+
+
+class AlignmentSegmentItem(PropertyGroup):
+    """Property group for displaying alignment segments in a UIList"""
+
+    name: StringProperty(name="Name", default="")
+    segment_type: StringProperty(name="Type", default="LINE")
+    length: FloatProperty(name="Length", default=0.0, unit="LENGTH")
+    ifc_id: IntProperty(name="IFC ID", default=0)
+
+
+class AlignmentDisplayRow(PropertyGroup):
+    """Property group for interleaved point/segment display in the table.
+
+    This creates the Civil 3D-style view where points and segments
+    are shown on separate rows:
+        Point 1 (End)
+          Segment 1 (Tan)
+        Point 2 (Tan)
+          Segment 2 (Tan)
+        ...
+    """
+
+    # Row type discriminator
+    row_type: EnumProperty(
+        name="Row Type",
+        items=[
+            ("POINT", "Point", "A PI point row"),
+            ("SEGMENT", "Segment", "A segment row between points"),
+        ],
+        default="POINT",
+    )
+
+    # Segment number (1, 2, 3...) - only for SEGMENT rows
+    segment_number: IntProperty(name="Segment #", default=0)
+
+    # Point index in the pis collection - for both types
+    # For POINT rows: the PI index
+    # For SEGMENT rows: the starting PI index of this segment
+    pi_index: IntProperty(name="PI Index", default=0)
+
+    # Display type string (End, Tan, Curve for points; Tan, Curve for segments)
+    display_type: StringProperty(name="Type", default="")
+
+    # Point coordinates (only for POINT rows)
+    x: FloatProperty(name="X", default=0.0, precision=3, unit="LENGTH")
+    y: FloatProperty(name="Y", default=0.0, precision=3, unit="LENGTH")
+
+    # Segment properties (only for SEGMENT rows)
+    length: FloatProperty(name="Length", default=0.0, precision=2, unit="LENGTH")
+    radius: FloatProperty(name="Radius", default=0.0, precision=2, unit="LENGTH")
+    arc_length: FloatProperty(name="Arc Length", default=0.0, precision=2, unit="LENGTH")
+
+
+class SaikeiAlignmentProperties(PropertyGroup):
+    """Properties for the alignment module"""
+
+    # Active alignment selection
+    active_alignment_id: IntProperty(
+        name="Active Alignment ID",
+        description="IFC entity ID of the active alignment",
+        default=0,
+    )
+
+    active_alignment_name: StringProperty(
+        name="Active Alignment",
+        description="Name of the currently active alignment",
+        default="",
+    )
+
+    # New alignment creation properties
+    new_alignment_name: StringProperty(
+        name="Name",
+        description="Name for new alignment",
+        default="Alignment 1",
+    )
+
+    start_station: FloatProperty(
+        name="Start Station",
+        description="Starting station value (e.g., 10000 for 100+00)",
+        default=10000.0,
+        min=0.0,
+    )
+
+    # PI collection for PI method creation
+    pis: CollectionProperty(type=AlignmentPI)
+    active_pi_index: IntProperty(name="Active PI", default=0)
+
+    # Segment display
+    segments: CollectionProperty(type=AlignmentSegmentItem)
+    active_segment_index: IntProperty(name="Active Segment", default=0)
+
+    # Combined point/segment display rows (for Civil 3D-style table)
+    display_rows: CollectionProperty(type=AlignmentDisplayRow)
+    active_display_row_index: IntProperty(name="Active Display Row", default=0)
+
+    # Editing state
+    is_editing: BoolProperty(
+        name="Is Editing",
+        description="Whether alignment is being edited",
+        default=False,
+    )
+
+    # Display options
+    show_pi_markers: BoolProperty(
+        name="Show PI Markers",
+        description="Show PI markers in viewport",
+        default=True,
+    )
+
+    show_station_labels: BoolProperty(
+        name="Show Station Labels",
+        description="Show station labels along alignment",
+        default=True,
+    )
+
+    station_interval: FloatProperty(
+        name="Station Interval",
+        description="Interval between station markers",
+        default=100.0,
+        min=1.0,
+        unit="LENGTH",
+    )
diff --git a/src/bonsai/bonsai/bim/module/alignment/ui.py b/src/bonsai/bonsai/bim/module/alignment/ui.py
new file mode 100644
index 0000000000..6e9224830a
--- /dev/null
+++ b/src/bonsai/bonsai/bim/module/alignment/ui.py
@@ -0,0 +1,366 @@
+# ==============================================================================
+# Saikei Civil - Civil Engineering Tools for Blender
+# Copyright (c) 2025 Michael Yoder / Desert Springs Civil Engineering PLLC
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
+#
+# Primary Author: Michael Yoder
+# Company: Desert Springs Civil Engineering PLLC
+# ==============================================================================
+
+
+"""UI panels for the alignment module
+
+All panels appear in the VIEW_3D N-panel under the "Saikei Civil" tab.
+"""
+
+import bpy
+from bpy.types import Panel, UIList
+
+
+def get_ifc_file():
+    """Get the current IFC file from Bonsai"""
+    try:
+        import bonsai.tool as tool
+
+        return tool.Ifc.get()
+    except (ImportError, AttributeError):
+        return None
+
+
+def is_ifc4x3():
+    """Check if the current IFC file is IFC4X3 schema"""
+    ifc = get_ifc_file()
+    return ifc is not None and ifc.schema == "IFC4X3"
+
+
+# =============================================================================
+# UILists
+# =============================================================================
+
+
+class SAIKEI_UL_alignment_pis(UIList):
+    """UIList for displaying interleaved points and segments (Civil 3D style)
+
+    Row types:
+    - POINT rows: End (endpoint), Mid (interior PI without curve)
+    - SEGMENT rows: Tan (tangent line), Curve (circular arc)
+
+    When a Mid point has radius > 0, it becomes a Curve segment row.
+    """
+
+    def draw_item(self, context, layout, data, item, icon, active_data, active_propname, index):
+        if self.layout_type in {"DEFAULT", "COMPACT"}:
+            row = layout.row(align=True)
+
+            if item.row_type == "POINT":
+                # Point row: No., Type, X, Y, Length, Radius
+                row.label(text="")  # No segment number for points
+
+                # Type with point/dot icon
+                # "End" = endpoint (POB/POE), "Mid" = interior PI point
+                row.label(text=item.display_type, icon="DOT")
+
+                # X, Y coordinates - get actual PI for editing
+                pi = data.pis[item.pi_index] if item.pi_index < len(data.pis) else None
+                if pi:
+                    sub = row.row(align=True)
+                    sub.prop(pi, "x", text="")
+                    sub.prop(pi, "y", text="")
+                else:
+                    row.label(text=f"{item.x:.2f}")
+                    row.label(text=f"{item.y:.2f}")
+
+                # Length column - empty for point rows
+                row.label(text="")
+
+                # Radius column - editable for Mid points (where curves can be added)
+                if item.display_type == "Mid" and pi:
+                    row.prop(pi, "radius", text="")
+                else:
+                    row.label(text="")
+
+            elif item.row_type == "SEGMENT":
+                if item.display_type == "Curve":
+                    # Curve segment row: No., Type (arc icon), X, Y, Arc Length, Radius
+                    row.label(text=f"{item.segment_number}")
+                    row.label(text="Curve", icon="SPHERECURVE")
+
+                    # Show PI coordinates on curve row
+                    row.label(text=f"{item.x:.2f}")
+                    row.label(text=f"{item.y:.2f}")
+
+                    # Arc length
+                    row.label(text=f"{item.arc_length:.2f}")
+
+                    # Radius - editable so user can modify or delete curve (set to 0)
+                    pi = data.pis[item.pi_index] if item.pi_index < len(data.pis) else None
+                    if pi:
+                        row.prop(pi, "radius", text="")
+                    else:
+                        row.label(text=f"{item.radius:.2f}")
+                else:
+                    # Tangent segment row: No., Type (line icon), -, -, Length, -
+                    row.label(text=f"{item.segment_number}")
+                    row.label(text="Tan", icon="IPO_LINEAR")
+
+                    # No X, Y for tangent segments
+                    row.label(text="")
+                    row.label(text="")
+
+                    # Length
+                    row.label(text=f"{item.length:.2f}")
+
+                    # No radius for tangent segments
+                    row.label(text="-")
+
+        elif self.layout_type == "GRID":
+            layout.alignment = "CENTER"
+            layout.label(text="", icon="DECORATE")
+
+
+# =============================================================================
+# Main Panel
+# =============================================================================
+
+
+class SAIKEI_PT_horizontal_alignment(Panel):
+    """Main Horizontal Alignment panel in the N-panel"""
+
+    bl_label = "Horizontal Alignment"
+    bl_idname = "SAIKEI_PT_horizontal_alignment"
+    bl_space_type = "VIEW_3D"
+    bl_region_type = "UI"
+    bl_category = "Saikei Civil"
+
+    def draw(self, context):
+        layout = self.layout
+        props = context.scene.SaikeiAlignmentProperties
+
+        # Status box
+        box = layout.box()
+        ifc = get_ifc_file()
+
+        if ifc is None:
+            box.label(text="No IFC file loaded", icon="ERROR")
+            box.label(text="Open an IFC4X3 file via Bonsai")
+            return
+
+        if ifc.schema != "IFC4X3":
+            box.label(text=f"Schema: {ifc.schema}", icon="ERROR")
+            box.label(text="Alignments require IFC4X3")
+            return
+
+        # IFC file is loaded and correct schema
+        row = box.row()
+        row.label(text="IFC4X3", icon="CHECKMARK")
+
+        # Count alignments
+        alignments = ifc.by_type("IfcAlignment")
+        row.label(text=f"Alignments: {len(alignments)}")
+
+        # Active alignment selector
+        if alignments:
+            box = layout.box()
+            box.label(text="Active Alignment:", icon="CURVE_PATH")
+            row = box.row()
+            row.prop(props, "active_alignment_name", text="")
+
+
+# =============================================================================
+# Creation Sub-Panel
+# =============================================================================
+
+
+class SAIKEI_PT_alignment_creation(Panel):
+    """Sub-panel for alignment creation tools"""
+
+    bl_label = "Creation"
+    bl_idname = "SAIKEI_PT_alignment_creation"
+    bl_space_type = "VIEW_3D"
+    bl_region_type = "UI"
+    bl_category = "Saikei Civil"
+    bl_parent_id = "SAIKEI_PT_horizontal_alignment"
+    bl_options = {"DEFAULT_CLOSED"}
+
+    @classmethod
+    def poll(cls, context):
+        return is_ifc4x3()
+
+    def draw(self, context):
+        layout = self.layout
+        props = context.scene.SaikeiAlignmentProperties
+
+        # New alignment properties
+        box = layout.box()
+        box.label(text="New Alignment:", icon="ADD")
+        box.prop(props, "new_alignment_name")
+        box.prop(props, "start_station")
+
+        # Creation operators
+        col = layout.column(align=True)
+        col.operator("saikei.create_alignment", icon="ADD")
+        col.operator("saikei.create_alignment_by_pi", icon="CURVE_PATH")
+        col.operator("saikei.import_alignment_csv", icon="IMPORT")
+
+
+# =============================================================================
+# PI Editor Sub-Panel
+# =============================================================================
+
+
+class SAIKEI_PT_pi_editor(Panel):
+    """Sub-panel for PI point table editor (Civil 3D style grid view)"""
+
+    bl_label = "PI Editor"
+    bl_idname = "SAIKEI_PT_pi_editor"
+    bl_space_type = "VIEW_3D"
+    bl_region_type = "UI"
+    bl_category = "Saikei Civil"
+    bl_parent_id = "SAIKEI_PT_horizontal_alignment"
+    bl_options = set()  # Open by default
+
+    @classmethod
+    def poll(cls, context):
+        return is_ifc4x3()
+
+    def draw(self, context):
+        layout = self.layout
+        props = context.scene.SaikeiAlignmentProperties
+
+        # Header row with column labels
+        header = layout.row(align=True)
+        header.label(text="No.")
+        header.label(text="Type")
+        header.label(text="X")
+        header.label(text="Y")
+        header.label(text="Length")
+        header.label(text="Radius")
+
+        # Combined point/segment list (interleaved view)
+        row = layout.row()
+        row.template_list(
+            "SAIKEI_UL_alignment_pis",
+            "",
+            props,
+            "display_rows",
+            props,
+            "active_display_row_index",
+            rows=8,
+        )
+
+        # Side buttons for list management
+        col = row.column(align=True)
+        col.operator("saikei.add_pi", icon="ADD", text="")
+        col.operator("saikei.remove_pi", icon="REMOVE", text="")
+        col.separator()
+        col.operator("saikei.pick_pi_from_viewport", icon="EYEDROPPER", text="")
+
+        # Active item details - show details based on selected row
+        if props.display_rows and 0 <= props.active_display_row_index < len(props.display_rows):
+            active_row = props.display_rows[props.active_display_row_index]
+
+            if active_row.row_type == "POINT" and active_row.pi_index < len(props.pis):
+                pi = props.pis[active_row.pi_index]
+
+                box = layout.box()
+                box.label(text=f"PI {active_row.pi_index + 1} Details:", icon="PROPERTIES")
+
+                row = box.row()
+                row.prop(pi, "pi_type", text="Type")
+
+                row = box.row(align=True)
+                row.prop(pi, "x", text="X")
+                row.prop(pi, "y", text="Y")
+
+                # Show radius for interior points (can add curve)
+                if pi.pi_type != "ENDPOINT":
+                    row = box.row()
+                    row.prop(pi, "radius", text="Radius")
+
+                # Display computed values
+                row = box.row()
+                row.label(text=f"Station: {pi.station:.2f}")
+                row.label(text=f"Length: {pi.length_to_next:.2f}")
+
+            elif active_row.row_type == "SEGMENT":
+                if active_row.display_type == "Curve":
+                    # Curve segment - show curve details with editable radius
+                    pi = props.pis[active_row.pi_index] if active_row.pi_index < len(props.pis) else None
+
+                    box = layout.box()
+                    box.label(text=f"Curve {active_row.segment_number} Details:", icon="SPHERECURVE")
+
+                    row = box.row()
+                    row.label(text=f"PI Location: ({active_row.x:.2f}, {active_row.y:.2f})")
+
+                    row = box.row()
+                    row.label(text=f"Arc Length: {active_row.arc_length:.2f}")
+
+                    # Editable radius
+                    if pi:
+                        row = box.row()
+                        row.prop(pi, "radius", text="Radius")
+                    else:
+                        row = box.row()
+                        row.label(text=f"Radius: {active_row.radius:.2f}")
+                else:
+                    # Tangent segment
+                    box = layout.box()
+                    box.label(text=f"Tangent {active_row.segment_number} Details:", icon="IPO_LINEAR")
+
+                    row = box.row()
+                    row.label(text=f"Length: {active_row.length:.2f}")
+
+        # Bottom actions
+        layout.separator()
+        row = layout.row(align=True)
+        row.operator("saikei.recalculate_pis", icon="FILE_REFRESH", text="Recalculate")
+        row.operator("saikei.clear_pis", icon="TRASH", text="Clear All")
+
+
+# =============================================================================
+# Stationing Sub-Panel
+# =============================================================================
+
+
+class SAIKEI_PT_alignment_stationing(Panel):
+    """Sub-panel for stationing and referents"""
+
+    bl_label = "Stationing"
+    bl_idname = "SAIKEI_PT_alignment_stationing"
+    bl_space_type = "VIEW_3D"
+    bl_region_type = "UI"
+    bl_category = "Saikei Civil"
+    bl_parent_id = "SAIKEI_PT_horizontal_alignment"
+    bl_options = {"DEFAULT_CLOSED"}
+
+    @classmethod
+    def poll(cls, context):
+        return is_ifc4x3()
+
+    def draw(self, context):
+        layout = self.layout
+        props = context.scene.SaikeiAlignmentProperties
+
+        # Station display options
+        box = layout.box()
+        box.label(text="Display:", icon="HIDE_OFF")
+        box.prop(props, "show_station_labels")
+        box.prop(props, "station_interval")
+
+        layout.separator()
+
+        # Stationing operators
+        col = layout.column(align=True)
+        col.operator("saikei.add_stationing_referent", icon="EMPTY_AXIS")
+        col.operator("saikei.name_segments", icon="FONT_DATA")