init

2026-10-21 19:32:02 -04:00
commit b74d278c8e
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+var GeodeticCoord = require('./coords/geodetic.js');
+var MagneticElements = require('./magnetic_elements.js');
+var MagneticVector = require('./magnetic_vector.js');
+
+module.exports = Model;
+
+function Model(options){
+	this.epoch = options.epoch;
+	this.start_date = new Date(options.start_date);
+	this.end_date = new Date(options.end_date);
+	this.name = options.name || "";
+	this.main_field_coeff_g = options.main_field_coeff_g || [0];
+	this.main_field_coeff_h = options.main_field_coeff_h || [0];
+	this.secular_var_coeff_g = options.secular_var_coeff_g || [0];
+	this.secular_var_coeff_h = options.secular_var_coeff_h || [0];
+	this.n_max = options.n_max || 0;
+	this.n_max_sec_var = options.n_max_sec_var || 0;
+	this.num_terms = this.n_max*(this.n_max+1)/2 + this.n_max;
+}
+
+Model.prototype.getTimedModel = function(date, allowOutOfBoundsModel = false){
+	var year_int = date.getUTCFullYear();
+	var fractional_year = (date.valueOf() - Date.UTC(year_int)) / (1000*3600*24*365);
+	var year = year_int + fractional_year;
+	var dyear = year - this.epoch;
+
+	if(date < this.start_date || date > this.end_date){
+		if(allowOutOfBoundsModel) {
+			console.error("Model is only valid from "+this.start_date.toDateString()+" to "+this.end_date.toDateString());
+		} else {
+			throw new Error("Model is only valid from "+this.start_date.toDateString()+" to "+this.end_date.toDateString());
+		}
+	}
+
+	var model = new Model({
+		epoch: this.epoch,
+		n_max: this.n_max,
+		n_max_sec_var: this.n_max_sec_var,
+		name: this.name,
+		start_date: this.start_date,
+		end_date: this.end_date,
+	});
+	var a = model.n_max_sec_var;
+	var b = a*(a + 1)/2 + a;
+	for(var n = 1; n <= this.n_max; n++){
+		for(var m = 0; m <= n; m++){
+			var i = n * (n + 1)/2 + m;
+			var hnm = this.main_field_coeff_h[i];
+			var gnm = this.main_field_coeff_g[i];
+			var dhnm = this.secular_var_coeff_h[i];
+			var dgnm = this.secular_var_coeff_g[i];
+			if(i <= b){
+				model.main_field_coeff_h[i] = hnm + dyear*dhnm;
+				model.main_field_coeff_g[i] = gnm + dyear*dgnm;
+				model.secular_var_coeff_h[i] = dhnm;
+				model.secular_var_coeff_g[i] = dgnm;
+			} else {
+				model.main_field_coeff_h[i] = hnm;
+				model.main_field_coeff_g[i] = gnm;
+			}
+		}
+	}
+	return model;
+};
+
+Model.prototype.getSummation = function(legendre, sph_variables, coord_spherical){
+	var bx = 0;
+	var by = 0;
+	var bz = 0;
+	var n, m, i, k;
+	var relative_radius_power = sph_variables.relative_radius_power;
+	var cos_mlambda = sph_variables.cos_mlambda;
+	var sin_mlambda = sph_variables.sin_mlambda;
+	var g = this.main_field_coeff_g;
+	var h = this.main_field_coeff_h;
+
+	for(n = 1; n <= this.n_max; n++){
+		for(m = 0; m <= n; m++){
+			i = n*(n+1)/2 + m;
+			bz -= relative_radius_power[n] *
+				(g[i]*cos_mlambda[m] + h[i]*sin_mlambda[m]) *
+				(n+1) * legendre.pcup[i];
+			by += relative_radius_power[n] *
+				(g[i]*sin_mlambda[m] - h[i]*cos_mlambda[m]) *
+				(m) * legendre.pcup[i];
+			bx -= relative_radius_power[n] *
+				(g[i]*cos_mlambda[m] + h[i]*sin_mlambda[m]) *
+				legendre.dpcup[i];
+		}
+	}
+	var cos_phi = Math.cos(Math.PI/180 * coord_spherical.phig);
+	if(Math.abs(cos_phi) > 1e-10){
+		by = by / cos_phi;
+	} else {
+		//special calculation around poles
+		by = 0;
+		var schmidt_quasi_norm1 = 1.0, schmidt_quasi_norm2, schmidt_quasi_norm3;
+		var pcup_s = [1];
+		var sin_phi = Math.sin(Math.PI/180 * coord_spherical.phig);
+
+		for(n = 1; n <= this.n_max; n++){
+			i = n*(n+1)/2 + 1;
+			schmidt_quasi_norm2 = schmidt_quasi_norm1 * (2*n-1) / n;
+			schmidt_quasi_norm3 = schmidt_quasi_norm2 * Math.sqrt(2*n/(n+1));
+			schmidt_quasi_norm1 = schmidt_quasi_norm2;
+			if(n == 1){
+				pcup_s[n] = pcup_s[n-1];
+			} else {
+				k = ((n-1)*(n-1) - 1) / ((2*n-1)*(2*n-3));
+				pcup_s[n] = sin_phi * pcup_s[n-1] - k*pcup_s[n-2];
+			}
+			by += relative_radius_power[n] *
+				(g[i]*sin_mlambda[1] - h[i]*cos_mlambda[1]) *
+				pcup_s[n] * schmidt_quasi_norm3;
+		}
+	}
+	return new MagneticVector({
+		bx: bx, by: by, bz: bz
+	});
+};
+
+Model.prototype.point = function(coords) {
+	// Extract altitude if provided, otherwise default to 0
+	var altitude = (coords.length > 2 && typeof coords[2] === 'number') ? coords[2] : 0;
+
+	var coord_geodetic = new GeodeticCoord({
+		lat: coords[0],
+		lon: coords[1],
+		height_above_ellipsoid: altitude
+	});
+	var coord_spherical = coord_geodetic.toSpherical();
+
+	var legendre = coord_spherical.getLegendreFunction(this.n_max);
+	var harmonic_variables = coord_spherical.getHarmonicVariables(coord_geodetic.ellipsoid, this.n_max);
+
+	var magnetic_vector_sph = this.getSummation(legendre, harmonic_variables, coord_spherical);
+	var magnetic_vector_geo = magnetic_vector_sph.rotate(coord_spherical, coord_geodetic);
+
+	return MagneticElements.fromGeoMagneticVector(magnetic_vector_geo);
+};