geojson-precision-ts

geojson-precision-ts

English | 日本語

Remove meaningless precision from your GeoJSON. If your coordinates go out to 7+ digits, you are probably misrepresenting your data. Most scenarios in which GeoJSON is useful (i.e. web-related applications) do not require survey-grade precision, and a higher value is placed on a compact file size. Trimming the precision of coordinates can greatly reduce file size, while removing the appearance of fake high precision.

This fork is rewritten in typescript.

Installation

pnpm add geojson-precision-ts

Usage

parse(*geojson*, *precision*, *extrasPrecision*, *options*);
omit(*geojson*);

Parameter	Type	Default	Description
geojson	GeoJSON	undefined	geojson is a valid GeoJSON object, and can be of type Point, LineString, Polygon, MultiPoint, MultiPolygon, MultiLineString, GeometryCollection, Feature, or FeatureCollection. If you are unsure whether or not your GeoJSON object is valid, you can validate it using Ajv with the geojson-schema package.
precision	number	6	precision is a positive integer. If your specified precision value is greater than the precision of the input geometry, the output precision will be the same as the input. For example, if your input coordinates are [10.0, 20.0], and you specify a precision of 5, the output will be the same as the input.
extrasPrecision	number	2	extrasPrecision is a positive integer. If your specified extrasPrecision value is greater than the precision of the input geometry, the output precision will be the same as the input. For example, if your input coordinates are [10.0, 20.0], and you specify a precision of 5, the output will be the same as the input.
options	GeojsonPrecisionOption

options are bellows:

Option	Type	Default	Description
ignorePoint	boolean	false	Skip Point
ignoreLineString	boolean	false	Skip LineString
ignorePolygon	boolean	false	Skip Polygon
removeDuplicates	boolean	true	Delete points at the same coordinates.

omit() is an alias for parse(t, 0, 0, { removeDuplicates: true }), a function that removes all decimal coordinates from GeoJSON.

How do you choose tolerance?

Tolerance corresponds to how much resolution you can spare. Higher the tolerance, lower is your geometry's resolution. Tolerance is specified in degrees. The above table applies here too. The table gives a general idea on what tolerance to use for your task. For example, if you can allow an error of 1.11km (for example while plotting a big city map) set your tolerance to 0.01.

decimal
places   degrees          distance
-------  -------          --------
0        1                111  km
1        0.1              11.1 km
2        0.01             1.11 km
3        0.001            111  m
4        0.0001           11.1 m
5        0.00001          1.11 m
6        0.000001         11.1 cm
7        0.0000001        1.11 cm
8        0.00000001       1.11 mm

Example

parse() function

import { parse } from "geojson-precision-ts";

const trimmed = parse(
  {
    type: "Point",
    coordinates: [18.984375, 57.32652122521709],
  },
  3,
);

trimmed will now look like this:

{
  "type": "Point",
  "coordinates": [18.984, 57.326]
}

omit() function

This is useful when you want to pin a static image by specifying pixels.

import { parse } from "geojson-precision-ts";

const omitted = omit({
  type: "Point",
  coordinates: [18.984375, 57.32652122521709],
});

omiited will now look like this:

{
  "type": "Point",
  "coordinates": [18, 57]
}

CLI

Geojson-precision can also be used via the command line when installed globally (using -g).

Parameters

precision (-p)

A positive integer specifying coordinate precision

extras precision (-e)

A positive integer specifying extra coordinate precision for things like the z value when the coordinate is [longitude, latitude, elevation].

input

An input GeoJSON file

output

An output GeoJSON file

Other flags

• --ignore-point: Skip Point geometries.
• --ignore-line-string: Skip LineString geometries.
• --ignore-polygon: Skip Polygon geometries.
• --remove-duplicates: Remove consecutive duplicate points.

Example use

geojson-precision -p 4 input.json output.json

Inspiration

Concepts, ideas, etc borrowed to various degrees from:

• wellknown
• LilJSON

License

MIT

Original Version by jczaplew's geojson-precision.

TypeScript version by Logue.

• Stop mutation of original object feature by frankrowe.
• Skip each geometry type feature by andrewharvey.
• Remove duplicate points feature by matthewrj.