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AP_Declination.cpp
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AP_Declination.cpp
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/*
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* Adam M Rivera
* With direction from: Andrew Tridgell, Jason Short, Justin Beech
*
* Adapted from: http://www.societyofrobots.com/robotforum/index.php?topic=11855.0
* Scott Ferguson
* scottfromscott@gmail.com
*
*/
#include "AP_Declination.h"
#include <cmath>
#include <AP_Common/AP_Common.h>
#include <AP_Math/AP_Math.h>
/*
calculate magnetic field intensity and orientation
*/
bool AP_Declination::get_mag_field_ef(float latitude_deg, float longitude_deg, float &intensity_gauss, float &declination_deg, float &inclination_deg)
{
bool valid_input_data = true;
/* round down to nearest sampling resolution. On some platforms (e.g. clang on macOS),
the behaviour of implicit casts from int32 to float can be undefined thus making it explicit here. */
float min_lat = float(static_cast<int32_t>(static_cast<int32_t>(floorf(latitude_deg / SAMPLING_RES)) * SAMPLING_RES));
float min_lon = float(static_cast<int32_t>(static_cast<int32_t>(floorf(longitude_deg / SAMPLING_RES)) * SAMPLING_RES));
/* for the rare case of hitting the bounds exactly
* the rounding logic wouldn't fit, so enforce it.
*/
/* limit to table bounds - required for maxima even when table spans full globe range */
if (latitude_deg <= SAMPLING_MIN_LAT) {
min_lat = float(static_cast<int32_t>(SAMPLING_MIN_LAT));
valid_input_data = false;
}
if (latitude_deg >= SAMPLING_MAX_LAT) {
min_lat = float(static_cast<int32_t>(static_cast<int32_t>(latitude_deg / SAMPLING_RES) * SAMPLING_RES - SAMPLING_RES));
valid_input_data = false;
}
if (longitude_deg <= SAMPLING_MIN_LON) {
min_lon = float(static_cast<int32_t>(SAMPLING_MIN_LON));
valid_input_data = false;
}
if (longitude_deg >= SAMPLING_MAX_LON) {
min_lon = float(static_cast<int32_t>(static_cast<int32_t>(longitude_deg / SAMPLING_RES) * SAMPLING_RES - SAMPLING_RES));
valid_input_data = false;
}
/* find index of nearest low sampling point */
uint32_t min_lat_index = constrain_int32(static_cast<uint32_t>((-(SAMPLING_MIN_LAT) + min_lat) / SAMPLING_RES), 0, LAT_TABLE_SIZE - 2);
uint32_t min_lon_index = constrain_int32(static_cast<uint32_t>((-(SAMPLING_MIN_LON) + min_lon) / SAMPLING_RES), 0, LON_TABLE_SIZE -2);
/* calculate intensity */
float data_sw = intensity_table[min_lat_index][min_lon_index];
float data_se = intensity_table[min_lat_index][min_lon_index + 1];
float data_ne = intensity_table[min_lat_index + 1][min_lon_index + 1];
float data_nw = intensity_table[min_lat_index + 1][min_lon_index];
/* perform bilinear interpolation on the four grid corners */
float data_min = ((longitude_deg - min_lon) / SAMPLING_RES) * (data_se - data_sw) + data_sw;
float data_max = ((longitude_deg - min_lon) / SAMPLING_RES) * (data_ne - data_nw) + data_nw;
intensity_gauss = ((latitude_deg - min_lat) / SAMPLING_RES) * (data_max - data_min) + data_min;
/* calculate declination */
data_sw = declination_table[min_lat_index][min_lon_index];
data_se = declination_table[min_lat_index][min_lon_index + 1];
data_ne = declination_table[min_lat_index + 1][min_lon_index + 1];
data_nw = declination_table[min_lat_index + 1][min_lon_index];
/* perform bilinear interpolation on the four grid corners */
data_min = ((longitude_deg - min_lon) / SAMPLING_RES) * (data_se - data_sw) + data_sw;
data_max = ((longitude_deg - min_lon) / SAMPLING_RES) * (data_ne - data_nw) + data_nw;
declination_deg = ((latitude_deg - min_lat) / SAMPLING_RES) * (data_max - data_min) + data_min;
/* calculate inclination */
data_sw = inclination_table[min_lat_index][min_lon_index];
data_se = inclination_table[min_lat_index][min_lon_index + 1];
data_ne = inclination_table[min_lat_index + 1][min_lon_index + 1];
data_nw = inclination_table[min_lat_index + 1][min_lon_index];
/* perform bilinear interpolation on the four grid corners */
data_min = ((longitude_deg - min_lon) / SAMPLING_RES) * (data_se - data_sw) + data_sw;
data_max = ((longitude_deg - min_lon) / SAMPLING_RES) * (data_ne - data_nw) + data_nw;
inclination_deg = ((latitude_deg - min_lat) / SAMPLING_RES) * (data_max - data_min) + data_min;
return valid_input_data;
}
/*
calculate magnetic field intensity and orientation
*/
float AP_Declination::get_declination(float latitude_deg, float longitude_deg)
{
float declination_deg=0, inclination_deg=0, intensity_gauss=0;
get_mag_field_ef(latitude_deg, longitude_deg, intensity_gauss, declination_deg, inclination_deg);
return declination_deg;
}
/*
get earth field as a Vector3f in Gauss given a Location
*/
Vector3f AP_Declination::get_earth_field_ga(const Location &loc)
{
float declination_deg=0, inclination_deg=0, intensity_gauss=0;
get_mag_field_ef(loc.lat*1.0e-7f, loc.lng*1.0e-7f, intensity_gauss, declination_deg, inclination_deg);
// create earth field
Vector3f mag_ef = Vector3f(intensity_gauss, 0.0, 0.0);
Matrix3f R;
R.from_euler(0.0f, -ToRad(inclination_deg), ToRad(declination_deg));
mag_ef = R * mag_ef;
return mag_ef;
}