68 lines
2.4 KiB
Dart
68 lines
2.4 KiB
Dart
import 'dart:typed_data';
|
|
import 'package:flutter/services.dart';
|
|
|
|
class GeoidGrid {
|
|
final double southLat, westLon, latStep, lonStep;
|
|
final int nRows, nCols;
|
|
final Float32List grid; // big-endian, south-to-north
|
|
|
|
GeoidGrid._(this.southLat, this.westLon, this.latStep, this.lonStep,
|
|
this.nRows, this.nCols, this.grid);
|
|
|
|
static Future<GeoidGrid> load(String assetPath) async {
|
|
final bytes = (await rootBundle.load(assetPath)).buffer.asByteData();
|
|
final southLat = bytes.getFloat64(0, Endian.big);
|
|
final westLon = bytes.getFloat64(8, Endian.big);
|
|
final latStep = bytes.getFloat64(16, Endian.big);
|
|
final lonStep = bytes.getFloat64(24, Endian.big);
|
|
final nRows = bytes.getInt32(32, Endian.big);
|
|
final nCols = bytes.getInt32(36, Endian.big);
|
|
|
|
final grid = Float32List(nRows * nCols);
|
|
for (int i = 0; i < grid.length; i++) {
|
|
grid[i] = bytes.getFloat32(40 + i * 4, Endian.big);
|
|
}
|
|
return GeoidGrid._(southLat, westLon, latStep, lonStep, nRows, nCols, grid);
|
|
}
|
|
|
|
/// Returns EHT2014 geoid undulation [m] at (lat, lon) via bilinear interpolation.
|
|
/// Returns null if outside grid or in no-data area.
|
|
double? getUndulation(double lat, double lon) {
|
|
final rowF = (lat - southLat) / latStep;
|
|
final colF = (lon - westLon) / lonStep;
|
|
final r0 = rowF.floor();
|
|
final c0 = colF.floor();
|
|
if (r0 < 0 || r0 >= nRows - 1 || c0 < 0 || c0 >= nCols - 1) return null;
|
|
|
|
final dr = rowF - r0;
|
|
final dc = colF - c0;
|
|
|
|
double v(int r, int c) => grid[r * nCols + c].toDouble();
|
|
final noData = -80.0;
|
|
final v00 = v(r0, c0);
|
|
if (v00 < noData) return null;
|
|
final v10 = v(r0 + 1, c0);
|
|
if (v10 < noData) return null;
|
|
final v01 = v(r0, c0 + 1);
|
|
if (v01 < noData) return null;
|
|
final v11 = v(r0 + 1, c0 + 1);
|
|
if (v11 < noData) return null;
|
|
|
|
return v00 * (1 - dr) * (1 - dc) +
|
|
v10 * dr * (1 - dc) +
|
|
v01 * (1 - dr) * dc +
|
|
v11 * dr * dc;
|
|
}
|
|
|
|
/// Orthometric height in the Hungarian EHT2014 system.
|
|
/// [nmea_ortho] = GGA field 9 (altitudeAboveMeanSeaLevel)
|
|
/// [nmea_sep] = GGA field 11 (geoidSeparation from receiver)
|
|
double? toEovHeight(
|
|
double lat, double lon, double nmeaOrtho, double nmeaSep) {
|
|
final nEht2014 = getUndulation(lat, lon);
|
|
if (nEht2014 == null) return null;
|
|
final ellipsoidal = nmeaOrtho + nmeaSep; // h = H + N_receiver
|
|
return ellipsoidal - nEht2014; // H_EOV = h - N_EHT2014
|
|
}
|
|
}
|