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Sphere.md

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Sphere Class

Overview

The Sphere class represents a spherical surface in 3D space. Spheres are fundamental 3D primitives used in modeling, collision detection, and geometric calculations.

Namespace

Autodesk.AutoCAD.Geometry

Key Properties

Property Type Description
Center Point3d Gets the center point of the sphere
Radius double Gets the radius of the sphere

Key Methods

Method Return Type Description
GetClosestPointTo(Point3d) Point3d Gets closest point on sphere surface
DistanceTo(Point3d) double Gets distance from point to sphere surface
IsOn(Point3d) bool Checks if point is on sphere surface
IsInside(Point3d) bool Checks if point is inside sphere

Code Examples

Example 1: Creating Spheres

// Create sphere at origin with radius 10
Point3d center = Point3d.Origin;
double radius = 10.0;

Sphere sphere = new Sphere(center, radius);

ed.WriteMessage($"\nSphere created");
ed.WriteMessage($"\nCenter: {sphere.Center}");
ed.WriteMessage($"\nRadius: {sphere.Radius}");
ed.WriteMessage($"\nSurface Area: {4 * Math.PI * radius * radius:F2}");
ed.WriteMessage($"\nVolume: {(4.0 / 3.0) * Math.PI * Math.Pow(radius, 3):F2}");

Example 2: Point-Sphere Relationship

Sphere sphere = new Sphere(new Point3d(0, 0, 0), 10.0);

Point3d insidePoint = new Point3d(5, 0, 0);
Point3d onSurface = new Point3d(10, 0, 0);
Point3d outsidePoint = new Point3d(15, 0, 0);

ed.WriteMessage($"\nInside point is inside: {sphere.IsInside(insidePoint)}");
ed.WriteMessage($"\nSurface point is on surface: {sphere.IsOn(onSurface)}");
ed.WriteMessage($"\nOutside point distance: {sphere.DistanceTo(outsidePoint):F2}");

Example 3: Finding Closest Point on Sphere

Sphere sphere = new Sphere(Point3d.Origin, 10.0);
Point3d testPoint = new Point3d(20, 20, 20);

Point3d closestPoint = sphere.GetClosestPointTo(testPoint);
double distance = sphere.DistanceTo(testPoint);

ed.WriteMessage($"\nTest point: {testPoint}");
ed.WriteMessage($"\nClosest point on sphere: {closestPoint}");
ed.WriteMessage($"\nDistance to surface: {distance:F4}");

Best Practices

  1. Radius: Must be positive
  2. Surface vs Volume: Use IsOn() for surface, IsInside() for volume
  3. Distance: Distance is to surface, not center
  4. Calculations: Surface area = 4πr², Volume = (4/3)πr³

Related Classes

  • Cylinder - Cylindrical surface
  • Cone - Conical surface
  • Torus - Toroidal surface
  • Point3d - Center and points on sphere

References