@programmerare/sweden_crs_transformations/src/transformation/transformer.ts

TypeScript/JavaScript library for transformation of geographic coordinates between WGS84 and the Swedish coordinate reference systems SWEREF99 and RT90

/*
* https://github.com/TomasJohansson/sweden_crs_transformations_4typescript
* Copyright (c) Tomas Johansson , http://www.programmerare.com
* The code in this 'sweden_crs_transformations_4typescript' library is licensed with MIT.
* The library is based on the C#.NET library 'sweden_crs_transformations_4net' (https://github.com/TomasJohansson/sweden_crs_transformations_4net)
* and the Dart library 'sweden_crs_transformations_4dart' (https://github.com/TomasJohansson/sweden_crs_transformations_4dart)
* Both above libraries are based on the C#.NET library 'MightyLittleGeodesy' (https://github.com/bjornsallarp/MightyLittleGeodesy/) 
* which is also released with MIT.
* License information about 'sweden_crs_transformations_4typescript' and 'MightyLittleGeodesy':
* https://github.com/TomasJohansson/sweden_crs_transformations_4typescript/blob/typescript_SwedenCrsTransformations/LICENSE
*/

import CrsCoordinate from '../crs_coordinate';
import CrsProjection from '../crs_projection';
import TransformStrategy from './transform_strategy';
import TransformStrategy_from_SWEREF99_or_RT90_to_WGS84 from './transform_strategy_from_sweref99_or_rt90_to_wgs84';
import TransformStrategy_from_WGS84_to_SWEREF99_or_RT90 from './transform_strategy_from_wgs84_to_sweref99_or_rt90';
import TransFormStrategy_From_Sweref99OrRT90_to_WGS84_andThenToRealTarget from './transform_strategy_from_sweref99_or_rt90_to_wgs84_and_then_to_real_target';

/** 
 * Intended to be an internal class, i.e. not exported from the library
 * (i.e. not exported from the file 'src/index.ts') 
 */
export default class Transformer {

  /** Implementation of transformations from WGS84 */
  private static readonly _transformStrategy_from_WGS84_to_SWEREF99_or_RT90: TransformStrategy = new TransformStrategy_from_WGS84_to_SWEREF99_or_RT90();

  /** Implementation of transformations to WGS84 */
  private static readonly _transformStrategy_from_SWEREF99_or_RT90_to_WGS84: TransformStrategy = new TransformStrategy_from_SWEREF99_or_RT90_to_WGS84();

  /** Implementation first transforming to WGS84 and then to the real target */
  private static readonly _transFormStrategy_From_Sweref99OrRT90_to_WGS84_andThenToRealTarget: TransformStrategy  = new TransFormStrategy_From_Sweref99OrRT90_to_WGS84_andThenToRealTarget();

  /**
   * Transforms a source {@link CrsCoordinate} (which includes the coordinate reference system as a property)
   * to a coordinate in another coordinate reference system i.e. the target {@link CrsProjection}
   * @param sourceCoordinate - The coordinate to become transformed.
   * @param targetCrsProjection - The coordinate reference system you want to transform to.
   */
  static transform(sourceCoordinate: CrsCoordinate, targetCrsProjection: CrsProjection): CrsCoordinate {
    if(sourceCoordinate.crsProjection == targetCrsProjection) return sourceCoordinate;

    let _transFormStrategy: TransformStrategy | null = null;

    // Transform FROM wgs84:
    if(
      sourceCoordinate.crsProjection.isWgs84()
      &&
      ( targetCrsProjection.isSweref() || targetCrsProjection.isRT90() )
    ) {
      _transFormStrategy = Transformer._transformStrategy_from_WGS84_to_SWEREF99_or_RT90;
    }

    // Transform TO wgs84:
    else if(
      targetCrsProjection.isWgs84()
      &&
      ( sourceCoordinate.crsProjection.isSweref() || sourceCoordinate.crsProjection.isRT90() )
    ) {
      _transFormStrategy = Transformer._transformStrategy_from_SWEREF99_or_RT90_to_WGS84;
    }

    // Transform between two non-wgs84:
    else if(
      ( sourceCoordinate.crsProjection.isSweref() || sourceCoordinate.crsProjection.isRT90() )
      &&
      ( targetCrsProjection.isSweref() || targetCrsProjection.isRT90() )
    ) {
      // the only direct transform supported is to/from WGS84, so therefore first transform to wgs84
      _transFormStrategy = Transformer._transFormStrategy_From_Sweref99OrRT90_to_WGS84_andThenToRealTarget;
    }

    if(_transFormStrategy != null) {
      return _transFormStrategy.transform(sourceCoordinate, targetCrsProjection);
    }

    throw new Error(`Unhandled source/target projection transformation: ${sourceCoordinate.crsProjection} ==> ${targetCrsProjection}`);
  }

}