cheap-ruler

A collection of fast approximations to common geographic measurements, along with some utility functions. Useful for speeding up analysis scripts when measuring things on a city scale, replacing Turf calls in key places.

Usage

var ruler = cheapRuler(35.05, 'miles');

var distance = ruler.distance([30.51, 50.32], [30.52, 50.312]);
var lineLength = ruler.lineDistance(line.geometry.coordinates);
var bbox = ruler.bufferPoint([30.5, 50.5], 0.01);

For a city scale (a few dozen miles) and far away from poles, the results are typically within 0.1% of corresponding Turf functions.

Note: to get the full performance benefit, create the ruler object once per an area of calculation (such as a tile), and then reuse it as much as possible.

Creating a ruler object

cheapRuler(latitude[, units])

Creates a ruler object that will approximate measurements around the given latitude. Units are either kilometers (default) or miles.

cheapRuler.fromTile(y, z[, units])

Creates a ruler object from tile coordinates (y and z). Convenient in tile-reduce scripts.

var ruler = cheapRuler.fromTile(1567, 12);

Ruler methods

distance(a, b)

Given two points of the form [x, y], returns the distance. 20–25 times faster than turf.distance.

lineDistance(line)

Given a line (an array of points), returns the total line distance. 20–25 times faster than turf.lineDistance.

area(polygon)

Given a polygon (an array of rings, where each ring is an array of points), returns the area. 3–4 times faster than turf.area. Note that it returns the value in the specified units (square kilometers by default) rather than square meters as in turf.area.

var area = ruler.area([[
    [-67.031, 50.458],
    [-67.031, 50.534],
    [-66.929, 50.534],
    [-66.929, 50.458],
    [-67.031, 50.458]
]]);

bearing(a, b)

Returns the bearing between two points in angles. 3–4 times faster than turf.bearing.

along(line, dist)

Returns the point at a specified distance along the line. 20-25 times faster than turf.along.

destination(p, dist, bearing)

Returns a new point given distance and bearing from the starting point. 6–7 times faster than turf.destination.

pointOnLine(line, p)

Returns an object of the form {point, index} where point is closest point on the line from the given point, and index is the start index of the segment with the closest point. 70–75 times faster than turf.pointOnLine.

lineSlice(start, stop, line)

Returns a part of the given line between the start and the stop points (or their closest points on the line). 50–60 times faster than turf.lineSlice.

bufferPoint(p, buffer)

Given a point, returns a bounding box object ([w, s, e, n]) created from the given point buffered by a given distance. About 200 times faster than creating a bounding box with two diagonal turf.destination calls.

var bbox = ruler.bufferPoint([30.5, 50.5], 0.01);

bufferBBox(bbox, buffer)

Given a bounding box, returns the box buffered by a given distance.

insideBBox(p, bbox)

Returns true if the given point is inside in the given bounding box, otherwise false.

Install

• NPM: npm install cheap-ruler
• Browser build (CDN): https://npmcdn.com/cheap-ruler@1.3.0/cheap-ruler.js