node-polygon

A JavaScript/TypeScript library for handling Polygon geometry according to OGC (Open Geospatial Consortium) standards with advanced geometric operations.

Features

• Create and manipulate Polygon geometries
• Support for WKT (Well-Known Text) format
• Geometric transformations including translation, scaling, and rotation
• Matrix-based transformations
• Polygon simplification using Douglas-Peucker algorithm
• Polygon smoothing using Catmull-Rom spline interpolation
• TypeScript support with full type definitions

Installation

npm install node-polygon

Usage

Basic Usage

import { Polygon, create, clone } from 'node-polygon';

// Create a new Polygon
const polygon = create();
polygon.coordinates = [[
  [-100, 40],
  [-105, 45],
  [-110, 55],
  [-100, 40]
]];

// Clone a polygon
const clonedPolygon = clone(polygon);

Working with WKT

import { Polygon, fromWKT } from 'node-polygon';

// Create polygon from WKT format
const polygon = new Polygon();
fromWKT(polygon, "POLYGON((116.36 39.90, 116.46 39.90, 116.56 39.90, 116.36 39.90))");
console.log(polygon.coordinates);

Geometric Transformations

import { Polygon, translate, scale, rotate, transformMat3 } from 'node-polygon';

const polygon = new Polygon();
polygon.coordinates = [[
  [10, 10],
  [20, 10],
  [20, 20],
  [10, 20],
  [10, 10]
]];

// Translation
translate(polygon, polygon, [5, 5]);

// Scaling
scale(polygon, polygon, [2, 2], [0, 0]);

// Rotation
rotate(polygon, polygon, Math.PI / 2, [0, 0]);

// Matrix transformation
const matrix = new Float32Array([1, 0, 0, 0, 1, 0, 10, 20, 1]);
transformMat3(polygon, polygon, matrix);

Polygon Simplification

import { Polygon, simplify } from 'node-polygon';

const complexPolygon = new Polygon();
// ... set complex coordinates ...

// Simplify polygon with tolerance value
const simplifiedPolygon = new Polygon();
simplify(simplifiedPolygon, complexPolygon, 0.01);

Polygon Smoothing

import { Polygon, smooth } from 'node-polygon';

const polygon = new Polygon();
// ... set coordinates ...

// Smooth polygon with default parameters
const smoothedPolygon = new Polygon();
smooth(smoothedPolygon, polygon);

// Smooth with custom tension and segment count
smooth(smoothedPolygon, polygon, 0.3, 15);

API Reference

Polygon Class

The main Polygon class representing a polygon geometry with the following properties:

• type: String - Always 'Polygon'
• coordinates: Array - Array of linear rings, each ring is an array of [x, y] coordinates

Functions

create(): Polygon

Creates a new empty Polygon object.

clone(a: Polygon): Polygon

Clones a Polygon object.

fromWKT(out: Polygon, wkt: string): void

Parses a Polygon from WKT format string (e.g., "POLYGON((116.36 39.90, 116.46 39.90, 116.56 39.90, 116.36 39.90))").

transformMat3(out: Polygon, a: Polygon, mat3: Float32Array): Polygon

Transforms a Polygon using a 3x3 matrix transformation.

translate(out: Polygon, a: Polygon, dxdy: number[]): Polygon

Translates a Polygon by dx and dy distances provided as an array.

scale(out: Polygon, a: Polygon, scalexy: number[], origin: number[] = [0, 0]): Polygon

Scales a Polygon by scale factors around an origin point.

rotate(out: Polygon, a: Polygon, rad: number, origin: number[] = [0, 0]): Polygon

Rotates a Polygon by radians around an origin point.

simplify(out: Polygon, a: Polygon, tolerance: number): Polygon

Simplifies a Polygon using the Douglas-Peucker algorithm with the given tolerance.

smooth(out: Polygon, a: Polygon, tension: number = 0.5, numOfSegments: number = 10): Polygon

Smooths a Polygon using Catmull-Rom spline interpolation with configurable tension and segment count.

Data Format

Polygon Structure

{
  "type": "Polygon",
  "coordinates": [
    [
      [-100, 40],
      [-105, 45],
      [-110, 55],
      [-100, 40]
    ]
  ]
}

WKT Format Support

Supports parsing POLYGON type WKT format:

POLYGON((116.36 39.90, 116.46 39.90, 116.56 39.90, 116.36 39.90))

License

MIT