Plane Struct

Overview

The Plane struct represents an infinite plane in 3D space, defined by a point on the plane and a normal vector perpendicular to it. Planes are used for mirroring, projections, coordinate system definitions, and geometric calculations.

Namespace

Autodesk.AutoCAD.Geometry

Key Properties

Property	Type	Description
`Normal`	`Vector3d`	Gets the normal vector perpendicular to the plane
`PointOnPlane`	`Point3d`	Gets a point on the plane

Constructors

Constructor	Description
`Plane(Point3d, Vector3d)`	Creates plane from point and normal vector
`Plane(Point3d, Point3d, Point3d)`	Creates plane from three non-collinear points
`Plane()`	Creates XY plane at origin

Key Methods

Method	Return Type	Description
`GetClosestPointTo(Point3d)`	`Point3d`	Gets closest point on plane to given point
`DistanceTo(Point3d)`	`double`	Gets signed distance from point to plane
`IsCoplanarTo(Plane)`	`bool`	Checks if coplanar with another plane
`IsPerpendicular(Plane)`	`bool`	Checks if perpendicular to another plane
`IsParallelTo(Plane)`	`bool`	Checks if parallel to another plane
`IsEqualTo(Plane)`	`bool`	Checks equality with default tolerance
`IsEqualTo(Plane, Tolerance)`	`bool`	Checks equality with custom tolerance

Code Examples

Example 1: Creating Planes

// XY plane at origin (Z = 0)
Plane xyPlane = new Plane();

// Plane from point and normal
Point3d origin = Point3d.Origin;
Vector3d normal = Vector3d.ZAxis;
Plane customPlane = new Plane(origin, normal);

// Plane from three points
Point3d p1 = new Point3d(0, 0, 0);
Point3d p2 = new Point3d(10, 0, 0);
Point3d p3 = new Point3d(0, 10, 0);
Plane planeFrom3Pts = new Plane(p1, p2, p3);

ed.WriteMessage($"\nXY Plane normal: {xyPlane.Normal}");
ed.WriteMessage($"\nCustom plane point: {customPlane.PointOnPlane}");
ed.WriteMessage($"\n3-point plane normal: {planeFrom3Pts.Normal}");

Example 2: Point-to-Plane Distance

// Create XY plane at Z = 0
Plane xyPlane = new Plane(Point3d.Origin, Vector3d.ZAxis);

// Test points
Point3d pt1 = new Point3d(5, 5, 10); // Above plane
Point3d pt2 = new Point3d(3, 3, -5); // Below plane
Point3d pt3 = new Point3d(7, 7, 0); // On plane

// Calculate signed distances
double dist1 = xyPlane.DistanceTo(pt1); // +10
double dist2 = xyPlane.DistanceTo(pt2); // -5
double dist3 = xyPlane.DistanceTo(pt3); // 0

ed.WriteMessage($"\nDistance pt1 to plane: {dist1:F2}");
ed.WriteMessage($"\nDistance pt2 to plane: {dist2:F2}");
ed.WriteMessage($"\nDistance pt3 to plane: {dist3:F2}");

// Positive = above plane (in direction of normal)
// Negative = below plane (opposite to normal)
// Zero = on plane

Example 3: Projecting Points onto Plane

// Create vertical plane (YZ plane at X = 0)
Plane yzPlane = new Plane(Point3d.Origin, Vector3d.XAxis);

// Point to project
Point3d testPoint = new Point3d(10, 5, 3);

// Get closest point on plane (projection)
Point3d projected = yzPlane.GetClosestPointTo(testPoint);

// Calculate projection distance
double distance = yzPlane.DistanceTo(testPoint);

ed.WriteMessage($"\nOriginal point: {testPoint}");
ed.WriteMessage($"\nProjected point: {projected}");
ed.WriteMessage($"\nProjection distance: {distance:F2}");

// Draw line showing projection
using (Transaction tr = db.TransactionManager.StartTransaction())
{
    Line projLine = new Line(testPoint, projected);
    projLine.ColorIndex = 1; // Red
    
    BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
    btr.AppendEntity(projLine);
    tr.AddNewlyCreatedDBObject(projLine, true);
    tr.Commit();
}

Example 4: Mirroring Across Plane

// Create mirror plane (YZ plane)
Plane mirrorPlane = new Plane(Point3d.Origin, Vector3d.XAxis);

// Create mirror transformation
Matrix3d mirror = Matrix3d.Mirroring(mirrorPlane);

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    // Select entity to mirror
    Entity ent = tr.GetObject(selectedId, OpenMode.ForWrite) as Entity;
    
    // Apply mirror transformation
    ent.TransformBy(mirror);
    
    tr.Commit();
}

ed.WriteMessage($"\nEntity mirrored across plane");
ed.WriteMessage($"\nPlane normal: {mirrorPlane.Normal}");
ed.WriteMessage($"\nPlane point: {mirrorPlane.PointOnPlane}");

Example 5: Checking Plane Relationships

// Create planes
Plane xyPlane = new Plane(Point3d.Origin, Vector3d.ZAxis);
Plane parallelPlane = new Plane(new Point3d(0, 0, 10), Vector3d.ZAxis);
Plane perpPlane = new Plane(Point3d.Origin, Vector3d.XAxis);

// Check relationships
bool isParallel = xyPlane.IsParallelTo(parallelPlane); // true
bool isPerpendicular = xyPlane.IsPerpendicular(perpPlane); // true
bool isCoplanar = xyPlane.IsCoplanarTo(parallelPlane); // false

ed.WriteMessage($"\nXY parallel to offset XY: {isParallel}");
ed.WriteMessage($"\nXY perpendicular to YZ: {isPerpendicular}");
ed.WriteMessage($"\nXY coplanar to offset XY: {isCoplanar}");

// Check if same plane
Plane samePlane = new Plane(new Point3d(5, 5, 0), Vector3d.ZAxis);
bool isCoplanar2 = xyPlane.IsCoplanarTo(samePlane); // true (same plane)

ed.WriteMessage($"\nXY coplanar to same plane: {isCoplanar2}");

Example 6: Creating Plane from Entity

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    // Get a planar entity (e.g., Circle, Region, Hatch)
    Circle circle = tr.GetObject(circleId, OpenMode.ForRead) as Circle;
    
    // Create plane from circle's properties
    Plane circlePlane = new Plane(circle.Center, circle.Normal);
    
    ed.WriteMessage($"\nCircle center: {circle.Center}");
    ed.WriteMessage($"\nCircle normal: {circle.Normal}");
    ed.WriteMessage($"\nPlane created from circle");
    
    // Check if point is on circle's plane
    Point3d testPt = new Point3d(10, 10, 0);
    double dist = circlePlane.DistanceTo(testPt);
    bool isOnPlane = Math.Abs(dist) < 0.001;
    
    ed.WriteMessage($"\nTest point on plane: {isOnPlane}");
    
    tr.Commit();
}

Example 7: Plane from Face Normal

// Create plane from three points defining a face
Point3d p1 = new Point3d(0, 0, 0);
Point3d p2 = new Point3d(10, 0, 0);
Point3d p3 = new Point3d(5, 10, 5);

// Calculate normal using cross product
Vector3d v1 = p1.GetVectorTo(p2);
Vector3d v2 = p1.GetVectorTo(p3);
Vector3d normal = v1.CrossProduct(v2).GetNormal();

// Create plane
Plane facePlane = new Plane(p1, normal);

// Alternative: use 3-point constructor
Plane facePlane2 = new Plane(p1, p2, p3);

ed.WriteMessage($"\nPlane from vectors - Normal: {facePlane.Normal}");
ed.WriteMessage($"\nPlane from 3 points - Normal: {facePlane2.Normal}");

Example 8: Checking Point Side of Plane

// Create horizontal plane at Z = 5
Plane plane = new Plane(new Point3d(0, 0, 5), Vector3d.ZAxis);

Point3d above = new Point3d(0, 0, 10);
Point3d below = new Point3d(0, 0, 2);
Point3d onPlane = new Point3d(5, 5, 5);

// Check which side of plane
double distAbove = plane.DistanceTo(above);
double distBelow = plane.DistanceTo(below);
double distOn = plane.DistanceTo(onPlane);

if (distAbove > 0.001)
    ed.WriteMessage("\nPoint is above plane (in normal direction)");
else if (distAbove < -0.001)
    ed.WriteMessage("\nPoint is below plane");
else
    ed.WriteMessage("\nPoint is on plane");

ed.WriteMessage($"\nDistances: above={distAbove:F2}, below={distBelow:F2}, on={distOn:F6}");

Common Patterns

Creating Construction Plane

// Get UCS plane
Editor ed = Application.DocumentManager.MdiActiveDocument.Editor;
Matrix3d ucs = ed.CurrentUserCoordinateSystem;
CoordinateSystem3d ucsCS = ucs.CoordinateSystem3d;

Plane ucsPlane = new Plane(ucsCS.Origin, ucsCS.Zaxis);

Checking if Points are Coplanar

Point3d p1 = new Point3d(0, 0, 0);
Point3d p2 = new Point3d(10, 0, 0);
Point3d p3 = new Point3d(0, 10, 0);
Point3d p4 = new Point3d(5, 5, 0);

// Create plane from first three points
Plane plane = new Plane(p1, p2, p3);

// Check if fourth point is on plane
double distance = plane.DistanceTo(p4);
bool isCoplanar = Math.Abs(distance) < 0.001;

ed.WriteMessage($"\nPoints are coplanar: {isCoplanar}");

Getting Perpendicular Plane

// Original plane (XY)
Plane xyPlane = new Plane(Point3d.Origin, Vector3d.ZAxis);

// Create perpendicular plane through X axis
Plane perpPlane = new Plane(Point3d.Origin, Vector3d.YAxis);

// Verify perpendicularity
bool isPerp = xyPlane.IsPerpendicular(perpPlane);
ed.WriteMessage($"\nPlanes perpendicular: {isPerp}");

Best Practices

Normal Direction: Ensure normal vector is normalized for consistent results
Three Points: When creating from 3 points, ensure they're not collinear
Signed Distance: Remember distance is signed (positive/negative based on normal)
Tolerance: Use tolerance when checking if points are on plane
Coordinate Systems: Planes are fundamental for UCS and coordinate transformations
Mirroring: Use planes for mirror transformations
Projections: Use GetClosestPointTo() for point-to-plane projections

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Plane Struct

Overview

Namespace

Key Properties

Constructors

Key Methods

Code Examples

Example 1: Creating Planes

Example 2: Point-to-Plane Distance

Example 3: Projecting Points onto Plane

Example 4: Mirroring Across Plane

Example 5: Checking Plane Relationships

Example 6: Creating Plane from Entity

Example 7: Plane from Face Normal

Example 8: Checking Point Side of Plane

Common Patterns

Creating Construction Plane

Checking if Points are Coplanar

Getting Perpendicular Plane

Best Practices

Related Classes

References

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Plane Struct

Overview

Namespace

Key Properties

Constructors

Key Methods

Code Examples

Example 1: Creating Planes

Example 2: Point-to-Plane Distance

Example 3: Projecting Points onto Plane

Example 4: Mirroring Across Plane

Example 5: Checking Plane Relationships

Example 6: Creating Plane from Entity

Example 7: Plane from Face Normal

Example 8: Checking Point Side of Plane

Common Patterns

Creating Construction Plane

Checking if Points are Coplanar

Getting Perpendicular Plane

Best Practices

Related Classes

References