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Tolerance.md

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Tolerance Struct

Overview

The Tolerance struct defines tolerance values for geometric comparisons in AutoCAD. It provides fuzzy equality testing for points, vectors, and other geometric entities to account for floating-point precision issues.

Namespace

Autodesk.AutoCAD.Geometry

Key Properties

Property Type Description
EqualPoint double Tolerance for point equality comparisons
EqualVector double Tolerance for vector equality comparisons
Global Tolerance (static) Gets the global default tolerance

Constructors

Constructor Description
Tolerance(double, double) Creates tolerance with point and vector tolerances

Code Examples

Example 1: Using Tolerance for Point Comparison

Point3d pt1 = new Point3d(10.0, 20.0, 0.0);
Point3d pt2 = new Point3d(10.0001, 20.0001, 0.0);

// Without tolerance (exact comparison)
bool exactEqual = pt1 == pt2; // false

// With tolerance
Tolerance tol = new Tolerance(0.001, 0.001);
bool fuzzyEqual = pt1.IsEqualTo(pt2, tol); // true

ed.WriteMessage($"\nExact equality: {exactEqual}");
ed.WriteMessage($"\nFuzzy equality (tol=0.001): {fuzzyEqual}");

Example 2: Using Global Tolerance

// Use AutoCAD's global tolerance settings
Tolerance globalTol = Tolerance.Global;

Point3d pt1 = new Point3d(5.0, 5.0, 0.0);
Point3d pt2 = new Point3d(5.00001, 5.00001, 0.0);

bool isEqual = pt1.IsEqualTo(pt2, globalTol);

ed.WriteMessage($"\nGlobal point tolerance: {globalTol.EqualPoint}");
ed.WriteMessage($"\nGlobal vector tolerance: {globalTol.EqualVector}");
ed.WriteMessage($"\nPoints equal with global tolerance: {isEqual}");

Example 3: Vector Comparison with Tolerance

Vector3d v1 = new Vector3d(1.0, 0.0, 0.0);
Vector3d v2 = new Vector3d(1.00001, 0.00001, 0.0);

Tolerance tol = new Tolerance(0.0001, 0.0001);
bool areEqual = v1.IsEqualTo(v2, tol);

ed.WriteMessage($"\nVectors equal: {areEqual}");

Example 4: Checking if Point is on Line

Point3d lineStart = new Point3d(0, 0, 0);
Point3d lineEnd = new Point3d(10, 0, 0);
Point3d testPoint = new Point3d(5.00001, 0.00001, 0);

// Calculate distance to line
Vector3d lineVec = lineStart.GetVectorTo(lineEnd);
Vector3d pointVec = lineStart.GetVectorTo(testPoint);
Vector3d cross = lineVec.CrossProduct(pointVec);
double distance = cross.Length / lineVec.Length;

// Check with tolerance
Tolerance tol = new Tolerance(0.001, 0.001);
bool isOnLine = distance < tol.EqualPoint;

ed.WriteMessage($"\nDistance to line: {distance:F6}");
ed.WriteMessage($"\nPoint on line (within tolerance): {isOnLine}");

Best Practices

  1. Use Tolerance: Always use tolerance for floating-point geometric comparisons
  2. Global Tolerance: Use Tolerance.Global for consistency with AutoCAD settings
  3. Appropriate Values: Choose tolerance values appropriate for your application scale
  4. Point vs Vector: Use different tolerances for points and vectors if needed

Related Classes

  • Point3d - Uses tolerance in IsEqualTo() method
  • Vector3d - Uses tolerance in IsEqualTo() method
  • Point2d - Uses tolerance for 2D comparisons
  • Vector2d - Uses tolerance for 2D vector comparisons

References