reproject-crs-geojson

!npm license
!npm version
!npm downloads

Small package to reproject the vertex coordinates of a GeoJSON between coordinate reference systems (CRS).

Accepts objects of type Feature, FeatureCollection, Geometry, or GeometryCollection, as well as all geometry types: Point, MultiPoint, LineString, MultiLineString, Polygon, MultiPolygon, and GeometryCollection.

The Turf.js coordEach function is used to iterate through all the object's coordinate pairs and reproject them with Proj4js. Additionally, to make CRS selection easier, proj4-list is added.

Documentation

https://f4gm.github.io/reproject-crs-geojson/

Usage

Install the package

``sh
npm install reproject-crs-geojson
`

Imports

`javascript
import {
reprojectGeoJSON,
getEPSG,
epsgExist,
toWGS84
} from "reproject-crs-geojson";
`

Reproject

The reprojectGeoJSON it does not affect the properties, geometry type or number of vertices, it only converts the CRS.

`javascript
import { reprojectGeoJSON } from "reproject-crs-geojson";

const Point = {
type: "Feature",
geometry: {
type: "Point",
coordinates: [1060479.7, 865010.7]
}
}

const converted = reprojectGeoJSON(
Point,
"EPSG:3115",
"EPSG:4326" // WGS84
);

console.log(converted);

// Expected

// {
// type: 'Feature',
// geometry: {
// type: 'Point',
// coordinates: [ -76.53327992507303, 3.3753051396728866 ]
// }
// }
`

You can also include the string PROJ.4:

`javascript
import { reprojectGeoJSON } from "reproject-crs-geojson";

const epsg_3115 = "+proj=tmerc +lat_0=4.59620041666667 +lon_0=-77.0775079166667 +k=1 +x_0=1000000 +y_0=1000000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs +type=crs";

const Point = {
type: "Feature",
geometry: {
type: "Point",
coordinates: [1060479.7, 865010.7]
}
}

const converted = reprojectGeoJSON(
Point,
epsg_3115,
"EPSG:4326" // WGS84
);
`

To convert directly to WGS84 (EPSG:4326) you can use the function toWGS84:

`javascript
import { toWGS84 } from "reproject-crs-geojson";

const epsg_3115 = "+proj=tmerc +lat_0=4.59620041666667 +lon_0=-77.0775079166667 +k=1 +x_0=1000000 +y_0=1000000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs +type=crs";

const Point = {
type: "Feature",
geometry: {
type: "Point",
coordinates: [1060479.7, 865010.7]
}
}

const converted = toWGS84(
Point,
epsg_3115
);

console.log(converted);
`

EPSG utils

If you want to know if an epsg code is in proj4-list:

`javascript
import { epsgExist } from "reproject-crs-geojson";

console.log(epsgExist("foo"));
// false

console.log(epsgExist("EPSG:3115"));
// true
`

If you need the PROJ.4 string:

`javascript
import { getEPSG } from "reproject-crs-geojson";

console.log(getEPSG("EPSG:4326"));
// +proj=longlat +datum=WGS84 +no_defs
``

> In theory, according to the specification, GeoJSON objects should be in the World Geodetic System 1984 (WGS 84). However, in many cases, we find it necessary to perform these types of transformations.

> This is my first npm package, as well as my first foray into the TypeScript language. I apologize in advance for any mistakes.