# proj4dart 3.0.0 Proj4dart is a Dart library to transform point coordinates from one coordinate system to another, including datum transformations (Dart version of proj4js/proj4js). ## Installing ``` export PUB_HOSTED_URL=https://pub.mirror.p-hatan.com flutter pub add proj4dart ``` Published: 2025-11-06T11:09:33.822852Z Expected archive SHA-256: ddcedc1f7876e62717de43ab3491e2829bdad0b028261805f94aa080967e5859 Available in cache; verification: upstream_checksum ## Direct dependencies - meta: ^1.3.0 - mgrs_dart: ^3.0.0 - wkt_parser: ^2.0.0 ## Package README (untrusted upstream documentation) # PROJ4DART > Proj4dart is a Dart library to transform point coordinates from one coordinate system to another, including datum transformations (Dart version of [proj4js/proj4js](https://github.com/proj4js/proj4js)). ## Installing Add proj4dart to `pubspec.yml` (dependencies section), then run `pub get` to download the new dependencies. ```yml dependencies: proj4dart: any # or the latest version on Pub ``` ## Using ### Predefined Projection There are 3 predefined Projections and 5 aliases by default: - [EPSG:4326](https://epsg.io/4326), which has the following alias: - WGS84 - [EPSG:4269](https://epsg.io/4269) - [EPSG:3857](https://epsg.io/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: ```dart 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](https://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](https://epsg.io/23700)): ```dart +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: ```dart 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](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](https://epsg.io/23700)): ```dart 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: ```dart 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](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](https://epsg.io/23700)): ```dart 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: ```dart 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](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: ```dart final bytes = await File( 'assets/my_grid.gsb', ).readAsBytes(); Projection.nadgrid('key', bytes); ``` Flutter: ```dart 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](https://proj.maptools.org/gen_parms.html). Nadgrid example: ```dart 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](example/proj4dart_shift_grid_example.dart) ### Transform between Projections ```dart 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 ```dart 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](test/data/all_proj4_defs.dart#L65)) - **5642** OGC WKT definitions ([test/data/all_proj4_ogc_wkt_defs.dart](test/data/all_proj4_ogc_wkt_defs.dart#L1029)) - **7426** ESRI WKT definitions ([test/data/all_proj4_esri_wkt_defs.dart](test/data/all_proj4_esri_wkt_defs.dart#L1083)) 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_results.dart), [test/results/all_proj4_ogc_wkt_results.dart](test/results/all_proj4_ogc_wkt_results.dart), [test/results/all_proj4_esri_wkt_results.dart](test/results/all_proj4_esri_wkt_results.dart)). The following table shows the avarage deltas of different Projections (using [EPSG:4326](https://epsg.io/4326.proj4) point of `[17.888058560281515, 46.89226406700879]` and transformed to [Custom CRS defined with Proj4 definition string](test/data/all_proj4_defs.dart#L65) 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](https://epsg.io/4326.proj4) point of `[17.888058560281515, 46.89226406700879]` and transformed to [EPSG:23700](https://epsg.io/23700.proj4) 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](https://epsg.io/4326.proj4) point of `[17.888058560281515, 46.89226406700879]` and transformed to [EPSG:23700](https://epsg.io/23700.proj4) 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](https://github.com/johnpryan/flutter_map). ## Authors Proj4dart was ported from proj4js by @maRci002 and [Gergely Padányi-Gulyás (@fegyi001)](https://twitter.com/fegyi001). ## Changelog # Changelog ## 3.0.0 - Update minimum Dart version to 3.0.0. - Update dependencies. ## 2.1.0 - Add nadgrids support ## 2.0.0 - Stable null safety release. - BREAKING CHANGE: `Projection('key')` syntax is no longer available since [factory constructors cannot return null value](https://dart.dev/null-safety/faq#how-should-i-migrate-a-factory-that-can-return-null) use `Projection.get('key')` instead. ## 1.0.5 - If WKT is Mercator projection then internal EPSG:3857 will be used - If WKT definition contains an encapsulated proj4 string definition then it will be used ## 1.0.4 - Named Projection returns null instead of throwing Exception if Projection not found by name - Some tests precalculate worst closeTos because these may depend on Dart version / OS ## 1.0.3 - add meta.dart to pubspec.yaml (avoid pub warning) ## 1.0.2 - Support ProjectionTuple - Support Projection.parse - Add more definitions - Add more tests - support exception compare - use blacklist when necessary - make closeTo even strict - Update wkt-parser-dart - fix axis order in some cases ## 1.0.1 - Support OGC WKT definitions - Support ESRI WKT definitions - Simplify globals logic ## 1.0.0 - Initial version - Can use 3 predefined projections + 5 aliases - Can create and use any custom projections with Proj4 string - Forward and inverse transformation between projections - Tested with ~4000 existing projections (from epsg.io)