mljsaffine-transform
Get and apply affine transform to 2D points.
Installation
$ npm i ml-affine-transform
Main steps of the algorithm to get the affine transform
Based on the tutorial: https://nghiaho.com/?page_id=671
- Find centroids of the two point sets and deduce the translation from one to the other
- Find rotation using SVD
When the transform is applied to a function, the operations are made in the following order:
- Rotate
- Scale
- Translate
API
The inputs of the functions are 3xN matrices consisting of the source and the destination points. The third dimension for Z must be padded with ones. The output is an object containing the x and y translations as well as the anti-clockwise angle in degrees.
export interface AffineTransformParameters {
rotation: number;
translation: { x: number; y: number };
scale: number;
}
export function getAffineTransform(
source: Matrix,
destination: Matrix,
): AffineTransformParameters;
Coordinates system
In this project, standard x and y axes are used, as in mathematics (y pointing up and x to the right). The angles are expressed in degrees and positive angles are in the anti-clockwise direction.
Example
import Matrix from 'ml-matrix';
import { getAffineTransform } from '../getAffineTransform';
const sourceMatrix = new Matrix([
[1, 1, -3], // x
[2, -1, -1], // y
[1, 1, 1], // z
]);
const destinationMatrix = new Matrix([
[4, -2, -2],
[-2, -2, 6],
[1, 1, 1],
]);
const result = getAffineTransform(sourceMatrix, destinationMatrix);
// result = {
// translation: { x: 0, y: 0 },
// scale: 2,
// rotation: -90,
// }