@turf/transform-scale

What is @turf/transform-scale?

@turf/transform-scale is a module from the Turf.js library that allows you to scale GeoJSON geometries. This can be useful for tasks such as resizing polygons, lines, and points by a given factor, either from their centroid or a specified origin.

What are @turf/transform-scale's main functionalities?

Scale a Polygon

This feature allows you to scale a polygon by a factor of 2. The polygon is scaled from its centroid by default.

const turf = require('@turf/turf');

const polygon = turf.polygon([[
  [-70.603637, -33.399918],
  [-70.614624, -33.395332],
  [-70.639343, -33.392466],
  [-70.659942, -33.394759],
  [-70.683975, -33.404504],
  [-70.697021, -33.419406],
  [-70.701141, -33.434306],
  [-70.700454, -33.446339],
  [-70.694274, -33.458369],
  [-70.682601, -33.465816],
  [-70.668869, -33.472117],
  [-70.646209, -33.473835],
  [-70.624923, -33.472117],
  [-70.609817, -33.468107],
  [-70.595397, -33.458369],
  [-70.587158, -33.442901],
  [-70.587158, -33.426283],
  [-70.590591, -33.414248],
  [-70.594711, -33.406224],
  [-70.603637, -33.399918]
]]);

const scaledPolygon = turf.transformScale(polygon, 2);
console.log(JSON.stringify(scaledPolygon));

Scale a LineString

This feature allows you to scale a LineString by a factor of 1.5. The line is scaled from its centroid by default.

const turf = require('@turf/turf');

const line = turf.lineString([
  [-70.603637, -33.399918],
  [-70.614624, -33.395332],
  [-70.639343, -33.392466],
  [-70.659942, -33.394759],
  [-70.683975, -33.404504]
]);

const scaledLine = turf.transformScale(line, 1.5);
console.log(JSON.stringify(scaledLine));

Scale a Point

This feature allows you to scale a point by a factor of 3. The point is scaled from its centroid by default, although for points, the scaling operation is trivial.

const turf = require('@turf/turf');

const point = turf.point([-70.603637, -33.399918]);

const scaledPoint = turf.transformScale(point, 3);
console.log(JSON.stringify(scaledPoint));

Other packages similar to @turf/transform-scale

jsts

JSTS is a JavaScript library of spatial predicates and functions for processing geometry. It provides a wide range of geometric operations, including scaling, but is more complex and feature-rich compared to @turf/transform-scale.

geolib

Geolib is a library to provide basic geospatial operations like distance calculation, conversion of units, and bounding boxes. While it does not focus on scaling geometries, it offers a variety of other geospatial utilities.

martinez-polygon-clipping

Martinez Polygon Clipping is a library for performing boolean operations on polygons. It can handle complex polygon operations but does not specifically focus on scaling geometries like @turf/transform-scale.

README

@turf/transform-scale

transformScale

Scale GeoJSON objects from a given point by a scaling factor e.g. factor=2 would make each object 200% larger. If a FeatureCollection is provided, the origin point will be calculated based on each individual feature unless an exact

Parameters

• geojson (GeoJSON | GeometryCollection) objects to be scaled

• factor number of scaling, positive values greater than 0. Numbers between 0 and 1 will shrink the geojson, numbers greater than 1 will expand it, a factor of 1 will not change the geojson.

• options Object Optional parameters (optional, default {})

  • options.origin (Corners | Coord) Point from which the scaling will occur (string options: sw/se/nw/ne/center/centroid) (optional, default 'centroid')
  • options.mutate boolean allows GeoJSON input to be mutated (significant performance improvement if true) (optional, default false)

Examples

const poly = turf.polygon([[[0,29],[3.5,29],[2.5,32],[0,29]]]);
const scaledPoly = turf.transformScale(poly, 3);

//addToMap
const addToMap = [poly, scaledPoly];
scaledPoly.properties = {stroke: '#F00', 'stroke-width': 4};

Returns (GeoJSON | GeometryCollection) scaled GeoJSON

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This module is part of the Turfjs project, an open source module collection dedicated to geographic algorithms. It is maintained in the Turfjs/turf repository, where you can create PRs and issues.

Installation

Install this single module individually:

$ npm install @turf/transform-scale

Or install the all-encompassing @turf/turf module that includes all modules as functions:

$ npm install @turf/turf