PROJ4DART

Proj4dart is a Dart library to transform point coordinates from one coordinate system to another, including datum transformations (Dart version of proj4js/proj4js).

Installing

Add proj4dart to pubspec.yml (dependencies section), then run pub get to download the new dependencies.

dependencies:
  proj4dart: any # or the latest version on Pub

Using

Predefined Projection

There are 3 predefined Projections and 5 aliases by default:

EPSG:4326, which has the following alias:
- WGS84
EPSG:4269
EPSG:3857, which has the following aliases:
- EPSG:3785
- GOOGLE
- EPSG:900913
- EPSG:102113

If you wish to use one of the predefined ones use Named Projection which has the following signature:

  var projection = Projection.get('EPSG:4326')!;

User-defined Projection

Proj4dart supports Proj4 definition strings, OGC WKT definitions and ESRI WKT definitions. They can be obtained from epsg.io.

With Proj4 string definition

If you wish to define your own projection you can create it with a valid Proj4 string (here for EPSG:23700):

+proj=somerc +lat_0=47.14439372222222 +lon_0=19.04857177777778 +k_0=0.99993 +x_0=650000 +y_0=200000 +ellps=GRS67 +towgs84=52.17,-71.82,-14.9,0,0,0,0 +units=m +no_defs

The signature is:

var def = '+proj=somerc +lat_0=47.14439372222222 +lon_0=19.04857177777778 +k_0=0.99993 +x_0=650000 +y_0=200000 +ellps=GRS67 +towgs84=52.17,-71.82,-14.9,0,0,0,0 +units=m +no_defs';

// Named Projection signature, later find it from anywhere via Projection.get('EPSG:23700')
var namedProjection = Projection.add('EPSG:23700', def);
// Projection without name signature
var projection = Projection.parse(def);

For full example visit example/proj4dart_example.dart

With OGC WKT definition

If you wish to define your own projection you can create it with a valid OGC WKT string (here for EPSG:23700):

PROJCS["HD72 / EOV",GEOGCS["HD72",DATUM["Hungarian_Datum_1972",SPHEROID["GRS 1967",6378160,298.247167427,AUTHORITY["EPSG","7036"]],TOWGS84[52.17,-71.82,-14.9,0,0,0,0],AUTHORITY["EPSG","6237"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4237"]],PROJECTION["Hotine_Oblique_Mercator_Azimuth_Center"],PARAMETER["latitude_of_center",47.14439372222222],PARAMETER["longitude_of_center",19.04857177777778],PARAMETER["azimuth",90],PARAMETER["rectified_grid_angle",90],PARAMETER["scale_factor",0.99993],PARAMETER["false_easting",650000],PARAMETER["false_northing",200000],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Y",EAST],AXIS["X",NORTH],AUTHORITY["EPSG","23700"]]

The signature is:

var def = 'PROJCS["HD72 / EOV",GEOGCS["HD72",DATUM["Hungarian_Datum_1972",SPHEROID["GRS 1967",6378160,298.247167427,AUTHORITY["EPSG","7036"]],TOWGS84[52.17,-71.82,-14.9,0,0,0,0],AUTHORITY["EPSG","6237"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4237"]],PROJECTION["Hotine_Oblique_Mercator_Azimuth_Center"],PARAMETER["latitude_of_center",47.14439372222222],PARAMETER["longitude_of_center",19.04857177777778],PARAMETER["azimuth",90],PARAMETER["rectified_grid_angle",90],PARAMETER["scale_factor",0.99993],PARAMETER["false_easting",650000],PARAMETER["false_northing",200000],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Y",EAST],AXIS["X",NORTH],AUTHORITY["EPSG","23700"]]';

// Named Projection signature, later find it from anywhere via Projection.get('EPSG:23700')
var namedProjection = Projection.add('EPSG:23700', def);
// Projection without name signature
var projection = Projection.parse(def);

For full example visit example/proj4dart_ogc_wkt_example.dart

With ESRI WKT definition

If you wish to define your own projection you can create it with a valid ESRI WKT string (here for EPSG:23700):

PROJCS["HD72_EOV",GEOGCS["GCS_HD72",DATUM["D_Hungarian_1972",SPHEROID["GRS_1967",6378160,298.247167427]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Hotine_Oblique_Mercator_Azimuth_Center"],PARAMETER["latitude_of_center",47.14439372222222],PARAMETER["longitude_of_center",19.04857177777778],PARAMETER["azimuth",90],PARAMETER["scale_factor",0.99993],PARAMETER["false_easting",650000],PARAMETER["false_northing",200000],UNIT["Meter",1]]

The signature is:

var def = 'PROJCS["HD72_EOV",GEOGCS["GCS_HD72",DATUM["D_Hungarian_1972",SPHEROID["GRS_1967",6378160,298.247167427]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Hotine_Oblique_Mercator_Azimuth_Center"],PARAMETER["latitude_of_center",47.14439372222222],PARAMETER["longitude_of_center",19.04857177777778],PARAMETER["azimuth",90],PARAMETER["scale_factor",0.99993],PARAMETER["false_easting",650000],PARAMETER["false_northing",200000],UNIT["Meter",1]]');

// Named Projection signature, later find it from anywhere via Projection.get('EPSG:23700')
var namedProjection = Projection.add('EPSG:23700', def);
// Projection without name signature
var projection = Projection.parse(def);

For full example visit example/proj4dart_esri_wkt_example.dart

Grid Based Datum Adjustments

To use +nadgrids= in a proj definition, first read your NTv2 .gsb file into an Uint8List, then pass to Projection.nadgrid. E.g:

Dart:

final bytes = await File(
  'assets/my_grid.gsb',
).readAsBytes();

Projection.nadgrid('key', bytes);

Flutter:

import 'package:flutter/services.dart' show rootBundle;
final bytes = (await rootBundle.load(fileName)).buffer.asUint8List();

Projection.nadgrid('key', bytes);

then use the given key in your definition, e.g. +nadgrids=@key,null. See Proj4 General Parameters.

Nadgrid example:

import 'package:flutter/services.dart' show rootBundle;

final bytes = (await rootBundle.load('assets/nzgd2kgrid0005.gsb')).buffer.asUint8List();
Projection.nadgrid('nzgd2kgrid0005.gsb', bytes);

var def = '+proj=longlat +datum=nzgd49 +towgs84=59.47,-5.04,187.44,0.47,-0.1,1.024,-4.5993 +nadgrids=nzgd2kgrid0005.gsb +no_defs';
var namedProjection = Projection.add('EPSG:4272', def);

For full example visit example/proj4dart_shift_grid_example.dart

Transform between Projections

import 'package:proj4dart/proj4dart.dart';

void main() {
  // Define Point
  var pointSrc = Point(x: 17.888058560281515, y: 46.89226406700879);

  // Use built-in projection
  var projSrc = Projection.get('EPSG:4326')!;

  // Find Projection by name or define it if not exists
  var projDst = Projection.get('EPSG:23700') ??
      Projection.add(
        'EPSG:23700',
        '+proj=somerc +lat_0=47.14439372222222 +lon_0=19.04857177777778 +k_0=0.99993 +x_0=650000 +y_0=200000 +ellps=GRS67 +towgs84=52.17,-71.82,-14.9,0,0,0,0 +units=m +no_defs',
      );

  // Forward transform (lonlat -> projected crs)
  var pointForward = projSrc.transform(projDst, pointSrc);
  print(
      'FORWARD: Transform point ${pointSrc.toArray()} from EPSG:4326 to EPSG:23700: ${pointForward.toArray()}');
  // FORWARD: Transform point [17.888058560281515, 46.89226406700879] from EPSG:4326 to EPSG:23700: [561651.8408065987, 172658.61998377228]

  // Inverse transform (projected crs -> lonlat)
  var pointInverse = projDst.transform(projSrc, pointForward);
  print(
      'INVERSE: Transform point ${pointForward.toArray()} from EPSG:23700 to EPSG:4326: ${pointInverse.toArray()}');
  // INVERSE: Transform point [561651.8408065987, 172658.61998377228] from EPSG:23700 to EPSG:4326: [17.888058565574845, 46.89226406698969]
}

Transform between Projections using ProjectionTuple

import 'package:proj4dart/proj4dart.dart';

void main() {
  // Define Point
  var pointSrc = Point(x: 17.888058560281515, y: 46.89226406700879);

  // Define ProjectionTuple which makes vice versa conversions even easier
  var tuple = ProjectionTuple(
    // Use built-in projection
    fromProj: Projection.get('EPSG:4326')!,
    // Define custom projection
    toProj: Projection.parse(
      '+proj=somerc +lat_0=47.14439372222222 +lon_0=19.04857177777778 +k_0=0.99993 +x_0=650000 +y_0=200000 +ellps=GRS67 +towgs84=52.17,-71.82,-14.9,0,0,0,0 +units=m +no_defs',
    ),
  );

  // Forward transform (lonlat -> projected crs)
  var pointForward = tuple.forward(pointSrc);
  print(
      'FORWARD: Transform point ${pointSrc.toArray()} from EPSG:4326 to EPSG:23700: ${pointForward.toArray()}');
  // FORWARD: Transform point [17.888058560281515, 46.89226406700879] from EPSG:4326 to EPSG:23700: [561651.8408065987, 172658.61998377228]

  // Inverse transform (projected crs -> lonlat)
  var pointInverse = tuple.inverse(pointForward);
  print(
      'INVERSE: Transform point ${pointForward.toArray()} from EPSG:23700 to EPSG:4326: ${pointInverse.toArray()}');
  // INVERSE: Transform point [561651.8408065987, 172658.61998377228] from EPSG:23700 to EPSG:4326: [17.888058565574845, 46.89226406698969]
}

Accuracy

Proj4dart was tested with

8444 Proj4 definitions (test/data/all_proj4_defs.dart)
5642 OGC WKT definitions (test/data/all_proj4_ogc_wkt_defs.dart)
7426 ESRI WKT definitions (test/data/all_proj4_esri_wkt_defs.dart)

Forward and inverse transformations were both performed and checked in each case. The expected forward and inverse results were pre-calculated using proj4js (test/results/all_proj4_results.dart, test/results/all_proj4_ogc_wkt_results.dart, test/results/all_proj4_esri_wkt_results.dart).

The following table shows the avarage deltas of different Projections (using EPSG:4326 point of [17.888058560281515, 46.89226406700879] and transformed to Custom CRS defined with Proj4 definition string which gave the forward result then transformed back the received forward result which gave the inverse result):

Projection	No. tests	avg delta forward_x	avg delta forward_y	avg delta inverse_x	avg delta inverse_y
Albers Projection	58	2.8260822953849e-9	1.6378431484617036e-9	1.0719394720518753e-14	1.0903155772870503e-14
Azimuthal Equidistant Projection	12	7.761021455128987e-11	1.5522042910257974e-10	1.7763568394002505e-15	1.1842378929335002e-15
Cassini Projection	33	3.9510654680656665e-10	3.3866275440562856e-10	3.2297397080004555e-16	0.0
Central Cylindrical Projection	5	0.0	0.0	0.0	0.0
Equidistant Conic Projection	9	1.2935035758548312e-11	0.0	1.578983857244667e-15	0.0
Equidistant Cylindrical Projection	25	0.0	0.0	0.0	0.0
Geocentric Projection	196	0.0	0.0	9.06304509898087e-17	0.0
Gnomic Projection	2	0.0	0.0	3.552713678800501e-15	0.0
Hotine Oblique Mercator Projection	51	4.460304683330012e-9	8.017819959158991e-9	6.339155779820502e-15	3.901018941428001e-15
Krovak Projection	9	9.054525030983819e-10	1.448724004957411e-9	1.578983857244667e-15	3.157967714489334e-15
Lambert Azimuthal Equal-Area Projection	20	5.820766091346741e-11	0.0	5.329070518200751e-16	0.0
Lambert Conformal Conic Projection	2028	1.8960008225716005e-8	1.2588414830372427e-8	4.613097105712702e-14	8.064379757884726e-14
LongLat	1152	1.6961740653995446e-16	0.0	2.312964634635743e-16	2.7755575615628914e-16
Miller Cylindrical Projection	2	0.0	0.0	0.0	0.0
Mollweide Projection	2	0.0	0.0	0.0	0.0
New Zealand Map Grid Projection	1	0.0	0.0	0.000003294908452744494	0.000008533214440831216
Orthographic Projection	2	0.0	0.0	7.105427357601002e-15	3.552713678800501e-15
Polyconic Projection	10	0.0	0.0	1.1842378929335002e-15	0.0
Pseudo Mercator Projection	25	0.0	3.7252902984619143e-10	1.4210854715202004e-16	2.842170943040401e-16
Robinson Projection	2	0.0	0.0	0.0	0.0
Sinusoidal Projection	3	0.0	0.0	0.0	0.0
Stereographic North Projection	21	2.217434701465425e-11	2.993536846978324e-10	4.906128413581644e-15	1.3534147347811431e-15
Stereographic South Projection	44	2.43414258446509e-10	2.063731004268861e-10	1.3726393759001935e-15	0.0
Swiss Oblique Mercator Projection	5	4.656612873077393e-11	0.0	1.4210854715202005e-15	0.0
Transverse Mercator Projection	3445	7.527289676908484e-12	5.01819311793899e-12	3.966550829771659e-13	3.0942861377693824e-13
Universal Transverse Mercator Projection	1279	3.4847229055075836e-10	3.429655454604303e-10	3.4304936617033767e-15	2.4999548951684524e-15
Van der Grinten Projection	2	3.3760443329811096e-9	2.3283064365386963e-9	0.0	0.0

Example (using EPSG:4326 point of [17.888058560281515, 46.89226406700879] and transformed to EPSG:23700 defined with Proj4 definition string):

LIBRARY	forward_x	forward_y	inverse_x	inverse_y
proj4dart	561651.8408065987	172658.61998377228	17.888058565574845	46.89226406698969
proj4js	561651.8408065989	172658.61998377228	17.888058565574852	46.89226406698969
delta	0.0000000002	0.0	0.000000000000007	0.0

In some cases also manual PostGIS testing (PostgreSQL 12.1, PostGIS 3.0.0 r17983) was performed such as the following (using EPSG:4326 point of [17.888058560281515, 46.89226406700879] and transformed to EPSG:23700 defined with Proj4 definition string):

LIBRARY	forward_x	forward_y	inverse_x	inverse_y
proj4dart	561651.8408065987	172658.61998377228	17.888058565574845	46.89226406698969
PostGIS	561651.8408065987	172658.6199837724	17.88805856557482	46.8922640683514
delta	0.0	0.00000000012	0.000000000000025	0.00000000136171

Used by

Proj4dart is currently the default projection handler of flutter_map.

Authors

Proj4dart was ported from proj4js by @maRci002 and Gergely Padányi-Gulyás (@fegyi001).

PROJ4DART

Installing

Using

Predefined Projection

User-defined Projection

With Proj4 string definition

With OGC WKT definition

With ESRI WKT definition

Grid Based Datum Adjustments

Transform between Projections

Transform between Projections using ProjectionTuple

Accuracy

Used by

Authors

Libraries

proj4dart package