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Proj4Projection

From-v3.3

Usage​

Reproject WGS84 coordinates to another CRS

import {Proj4Projection} from '@math.gl/proj4';

const nad83Proj =
  '+title=NAD83 (long/lat) +proj=longlat +a=6378137.0 +b=6356752.31414036 +ellps=GRS80 +datum=NAD83 +units=degrees';
const projection = new Proj4Projection({from: 'WGS84', to: nad83Proj});

const wgs84Position = [21, 78, 5000];
const reprojectedPosition = projection.project(wgs84Position);

Define Projection Aliases

import {Proj4Projection} from '@math.gl/proj4';

Proj4Projection.defineProjectionAliases({
  'EPSG:4326': '+title=WGS 84 (long/lat) +proj=longlat +ellps=WGS84 +datum=WGS84 +units=degrees',
  'EPSG:4269':
    '+title=NAD83 (long/lat) +proj=longlat +a=6378137.0 +b=6356752.31414036 +ellps=GRS80 +datum=NAD83 +units=degrees'
});
const projection = new Proj4Projection({from: 'EPSG:4326', to: 'EPSG:4269'});

Respect the axis order declared by a coordinate system

const projection = new Proj4Projection({
  from: '+proj=longlat +datum=WGS84 +axis=neu',
  to: 'EPSG:3857',
  enforceAxis: true
});

const position = projection.project([37.8, -122.4]);

Register an NTv2 datum grid before using it in a projection definition

const grid = await fetch('/grids/local-datum.gsb').then(response => response.arrayBuffer());
Proj4Projection.registerDatumGrid('local-datum.gsb', grid);

const projection = new Proj4Projection({
  from: '+proj=longlat +ellps=WGS84 +nadgrids=local-datum.gsb +no_defs',
  to: 'WGS84'
});

Static Fields​

Proj4Projection.defineProjectionAliases(projections: {[alias: string]: Proj4CRSDefinition})​

Defines projection aliases from authority codes, PROJ strings, WKT strings, or PROJJSON objects.

Proj4Projection.registerDatumGrid(name: string, grid: ArrayBuffer, options?: Proj4DatumGridOptions)​

Registers an NTv2 datum grid that projection definitions can reference with +nadgrids=<name>. Set options.includeErrorFields to false when the grid does not contain latitude and longitude error columns.

CRS compatibility utilities​

checkProj4CRSCompatibility(definition, options?)​

Checks whether a broad ReadonlyCRSDefinition can be constructed by proj4js. Mutable CRSDefinition values and deeply readonly definitions from SpatialReference are both accepted. It returns a structured result with status set to supported, unsupported, or unknown, along with checked, lossy, an optional CRS type, and a stable reason code.

For serialized WKT and PROJ strings, options.serialized can be probe (the default), unknown, or accept. Probing constructs a proj4js converter but does not transform any coordinates.

toProj4CRSDefinition(definition, options?)​

Narrows a broad readonly CRS definition to Proj4CRSDefinition. Supported object definitions are returned unchanged, and serialized definitions are passed through unchanged. Unsupported object types throw Proj4CRSCompatibilityError in the default strict mode.

Set options.mode to horizontal to explicitly extract the single Proj4-compatible horizontal component from a CompoundCRS. This is lossy and rejects compounds with no or multiple eligible horizontal components.

Methods​

constructor(options: Proj4ProjectionOptions)​

Create a new Proj4Projection instance that can convert between the specified coordinate systems.

  • from and to are Proj4CRSDefinition values. They can be named coordinate systems, PROJ strings, WKT strings, or the GeographicCRS, GeodeticCRS, ProjectedCRS, and BoundCRS PROJJSON object kinds supported by proj4js 2.20.9. Both default to WGS84.
  • enforceAxis defaults to false. Set it to true to respect the axis order declared by the source and destination coordinate systems.

project(coord: number[]): number[]​

Project a coordinate project from first to second coordinate system

unproject(coord: number[]): number[]​

Project a coordinate project from second to first coordinate system