Merge pull request #12 from maRci002/feat/nadgrids

add nadgrids

.vscode/launch.json

@@ -1,19 +1,29 @@
 {
   "version": "0.2.0",
-  "configurations": [{
-    "name": "Dart-proj4",
-    "program": "example/proj4dart_example.dart",
-    "request": "launch",
-    "type": "dart"
-  }, {
-    "name": "Dart-ogc-wkt",
-    "program": "example/proj4dart_ogc_wkt_example.dart",
-    "request": "launch",
-    "type": "dart"
-  }, {
-    "name": "Dart-esri-wkt",
-    "program": "example/proj4dart_esri_wkt_example.dart",
-    "request": "launch",
-    "type": "dart"
-  }]
+  "configurations": [
+    {
+      "name": "Dart-proj4",
+      "program": "example/proj4dart_example.dart",
+      "request": "launch",
+      "type": "dart"
+    },
+    {
+      "name": "Dart-ogc-wkt",
+      "program": "example/proj4dart_ogc_wkt_example.dart",
+      "request": "launch",
+      "type": "dart"
+    },
+    {
+      "name": "Dart-esri-wkt",
+      "program": "example/proj4dart_esri_wkt_example.dart",
+      "request": "launch",
+      "type": "dart"
+    },
+    {
+      "name": "Dart-shift-grid",
+      "program": "example/proj4dart_shift_grid_example.dart",
+      "request": "launch",
+      "type": "dart"
+    }
+  ]
 }

README.md

@@ -99,6 +99,43 @@ 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](http://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

example/proj4dart_shift_grid_example.dart

@@ -0,0 +1,41 @@
+import 'dart:io';
+
+import 'package:proj4dart/proj4dart.dart';
+
+void main() async {
+  // read bytes from filesystem
+  // In case of Flutter assets:
+  // import 'package:flutter/services.dart' show rootBundle;
+  // final bytes = (await rootBundle.load(fileName)).buffer.asUint8List();
+  final bytes = await File(
+    'test/test_resources/ntv2_0_downsampled.gsb',
+  ).readAsBytes();
+
+  // load nadgrid
+  Projection.nadgrid('ntv2', bytes);
+
+  // Define Point
+  var pointSrc = Point(x: -44.382211538462, y: 40.3768);
+
+  //  Define some projection which has '+nadgrids='
+  var projSrc = Projection.add(
+    'ntv2_from',
+    '+proj=longlat +ellps=clrk66 +nadgrids=@ignorable,ntv2,null',
+  );
+  ;
+
+  // Use built-in projection
+  var projDst = Projection.WGS84;
+
+  // Forward transform (projected crs -> lonlat)
+  var pointForward = projSrc.transform(projDst, pointSrc);
+  print(
+      'FORWARD: Transform point ${pointSrc.toArray()} from ntv2_from to WGS84: ${pointForward.toArray()}');
+  // FORWARD: Transform point [-44.382211538462, 40.3768] from ntv2_from to WGS84: [-44.38074905319326, 40.37745745991217]
+
+  // Inverse transform (lonlat -> projected crs)
+  var pointInverse = projDst.transform(projSrc, pointForward);
+  print(
+      'INVERSE: Transform point ${pointForward.toArray()} from WGS84 to ntv2_from: ${pointInverse.toArray()}');
+  // INVERSE: Transform point [-44.38074905319326, 40.37745745991217] from WGS84 to ntv2_from: [-44.38074905319326, 40.37745745991217]
+}

lib/src/classes/datum.dart

@@ -1,3 +1,4 @@
+import 'package:proj4dart/src/classes/nadgrid.dart';
 import 'package:proj4dart/src/constants/values.dart' as consts;
 
 class Datum {
@@ -7,13 +8,15 @@ class Datum {
   final double b;
   final double es;
   final double ep2;
+  final List<NadgridParam>? grids;
 
   Datum(String? datumCode, List<double>? datum_params, double a, double b,
-      double es, double ep2)
+      double es, double ep2, List<NadgridParam>? nadgrids)
       : a = a,
         b = b,
         es = es,
-        ep2 = ep2 {
+        ep2 = ep2,
+        grids = nadgrids {
     if (datumCode == null || datumCode == 'none') {
       datumType = consts.PJD_NODATUM;
     } else {
@@ -37,5 +40,9 @@ class Datum {
         }
       }
     }
+
+    if (nadgrids != null) {
+      datumType = consts.PJD_GRIDSHIFT;
+    }
   }
 }