Skip to content

Point2d.md

Latest commit

 

History

History
157 lines (120 loc) · 4.53 KB

Point2d.md

File metadata and controls

157 lines (120 loc) · 4.53 KB

Point2d Struct

Overview

The Point2d struct represents a point in 2D space with X and Y coordinates. It is used for planar geometry operations in the XY plane.

Namespace

Autodesk.AutoCAD.Geometry

Key Properties

Property Type Description
X double Gets the X coordinate
Y double Gets the Y coordinate
Origin Point2d (static) Gets the origin point (0, 0)

Key Methods

Method Return Type Description
Add(Vector2d) Point2d Adds a vector to the point
Subtract(Vector2d) Point2d Subtracts a vector from the point
GetVectorTo(Point2d) Vector2d Gets the vector from this point to another
DistanceTo(Point2d) double Calculates distance to another point
TransformBy(Matrix2d) Point2d Transforms the point by a matrix
RotateBy(double, Point2d) Point2d Rotates the point around another point
Mirror(Line2d) Point2d Mirrors the point across a line
ToArray() double[] Converts to array [X, Y]
IsEqualTo(Point2d) bool Checks equality

Code Examples

Example 1: Creating Points

// Create points
Point2d origin = Point2d.Origin; // (0, 0)
Point2d pt1 = new Point2d(10, 20);
Point2d pt2 = new Point2d(5.5, 7.3);

// From array
double[] coords = { 15, 25 };
Point2d pt3 = new Point2d(coords);

ed.WriteMessage($"\nPoint 1: ({pt1.X}, {pt1.Y})");
ed.WriteMessage($"\nPoint 2: ({pt2.X}, {pt2.Y})");

Example 2: Point Arithmetic

Point2d pt = new Point2d(10, 10);
Vector2d vec = new Vector2d(5, 3);

// Add vector
Point2d newPt = pt.Add(vec); // (15, 13)

// Subtract vector
Point2d movedPt = pt.Subtract(vec); // (5, 7)

// Get vector between points
Point2d pt1 = new Point2d(0, 0);
Point2d pt2 = new Point2d(10, 10);
Vector2d direction = pt1.GetVectorTo(pt2);

ed.WriteMessage($"\nDirection: ({direction.X}, {direction.Y})");

Example 3: Distance Calculations

Point2d pt1 = new Point2d(0, 0);
Point2d pt2 = new Point2d(10, 0);
Point2d pt3 = new Point2d(0, 10);

double dist12 = pt1.DistanceTo(pt2); // 10.0
double dist13 = pt1.DistanceTo(pt3); // 10.0
double dist23 = pt2.DistanceTo(pt3); // 14.14

ed.WriteMessage($"\nDistance pt1 to pt2: {dist12:F2}");
ed.WriteMessage($"\nDistance pt2 to pt3: {dist23:F2}");

Example 4: Transformations

Point2d pt = new Point2d(10, 0);

// Rotate 90°
Point2d rotated = pt.RotateBy(Math.PI / 2, Point2d.Origin);

// Transform by matrix
Matrix2d translation = Matrix2d.Displacement(new Vector2d(5, 10));
Point2d translated = pt.TransformBy(translation);

ed.WriteMessage($"\nRotated: ({rotated.X:F2}, {rotated.Y:F2})");
ed.WriteMessage($"\nTranslated: ({translated.X}, {translated.Y})");

Example 5: Converting to 3D

Point2d pt2d = new Point2d(10, 20);

// Convert to 3D (Z = 0)
Point3d pt3d = new Point3d(pt2d.X, pt2d.Y, 0);

ed.WriteMessage($"\n2D: ({pt2d.X}, {pt2d.Y})");
ed.WriteMessage($"\n3D: ({pt3d.X}, {pt3d.Y}, {pt3d.Z})");

// Convert from 3D to 2D
Point3d pt3dInput = new Point3d(5, 10, 15);
Point2d pt2dResult = new Point2d(pt3dInput.X, pt3dInput.Y);

ed.WriteMessage($"\n3D to 2D: ({pt2dResult.X}, {pt2dResult.Y})");

Common Patterns

Midpoint Calculation

Point2d pt1 = new Point2d(0, 0);
Point2d pt2 = new Point2d(20, 10);

Point2d midpoint = new Point2d(
    (pt1.X + pt2.X) / 2,
    (pt1.Y + pt2.Y) / 2
);

// Alternative using vectors
Vector2d halfVec = pt1.GetVectorTo(pt2) * 0.5;
Point2d midpoint2 = pt1.Add(halfVec);

Interpolation

Point2d start = new Point2d(0, 0);
Point2d end = new Point2d(10, 10);

// Get point 30% along the line
double t = 0.3;
Vector2d vec = start.GetVectorTo(end) * t;
Point2d interpolated = start.Add(vec);

Best Practices

  1. Use for 2D: Prefer Point2d over Point3d for planar operations
  2. Origin: Use Point2d.Origin instead of new Point2d(0, 0)
  3. Immutability: Point2d is a struct; operations return new points
  4. Tolerance: Use tolerance-based equality for comparisons
  5. Conversion: Easy conversion to/from Point3d when needed

Related Classes

  • Point3d - 3D point with X, Y, Z coordinates
  • Vector2d - 2D direction and magnitude
  • Matrix2d - 2D transformation matrix
  • Line2d - 2D line using two points

References