mirror of
https://github.com/PX4/PX4-Autopilot.git
synced 2026-05-25 08:36:08 +08:00
Added automatic declination lookup
This commit is contained in:
Lorenz Meier
@@ -48,6 +48,8 @@
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#include "uORB/topics/fence.h"
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#include "uORB/topics/vehicle_global_position.h"
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#include "geo/geo_mag_declination.h"
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__BEGIN_DECLS
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#include <stdbool.h>
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@@ -0,0 +1,135 @@
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/****************************************************************************
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*
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* Copyright (c) 2014 MAV GEO Library (MAVGEO). All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name MAVGEO nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/**
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* @file geo_mag_declination.c
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*
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* Calculation / lookup table for earth magnetic field declination.
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*
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* Lookup table from Scott Ferguson <scottfromscott@gmail.com>
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*
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* XXX Lookup table currently too coarse in resolution (only full degrees)
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* and lat/lon res - needs extension medium term.
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*
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*/
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/** set this always to the sampling in degrees for the table below */
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#define SAMPLING_RES 10
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#define SAMPLING_MIN_LAT -60.0f
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#define SAMPLING_MAX_LAT 60.0f
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#define SAMPLING_MIN_LON -180.0f
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#define SAMPLING_MAX_LON 180.0f
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static const char declination_table[13][37] = \
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{
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46, 45, 44, 42, 41, 40, 38, 36, 33, 28, 23, 16, 10, 4, -1, -5, -9, -14, -19, -26, -33, -40, -48, -55, -61, \
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-66, -71, -74, -75, -72, -61, -25, 22, 40, 45, 47, 46, 30, 30, 30, 30, 29, 29, 29, 29, 27, 24, 18, 11, 3, \
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-3, -9, -12, -15, -17, -21, -26, -32, -39, -45, -51, -55, -57, -56, -53, -44, -31, -14, 0, 13, 21, 26, \
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29, 30, 21, 22, 22, 22, 22, 22, 22, 22, 21, 18, 13, 5, -3, -11, -17, -20, -21, -22, -23, -25, -29, -35, \
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-40, -44, -45, -44, -40, -32, -22, -12, -3, 3, 9, 14, 18, 20, 21, 16, 17, 17, 17, 17, 17, 16, 16, 16, 13, \
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8, 0, -9, -16, -21, -24, -25, -25, -23, -20, -21, -24, -28, -31, -31, -29, -24, -17, -9, -3, 0, 4, 7, \
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10, 13, 15, 16, 12, 13, 13, 13, 13, 13, 12, 12, 11, 9, 3, -4, -12, -19, -23, -24, -24, -22, -17, -12, -9, \
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-10, -13, -17, -18, -16, -13, -8, -3, 0, 1, 3, 6, 8, 10, 12, 12, 10, 10, 10, 10, 10, 10, 10, 9, 9, 6, 0, -6, \
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-14, -20, -22, -22, -19, -15, -10, -6, -2, -2, -4, -7, -8, -8, -7, -4, 0, 1, 1, 2, 4, 6, 8, 10, 10, 9, 9, 9, \
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9, 9, 9, 8, 8, 7, 4, -1, -8, -15, -19, -20, -18, -14, -9, -5, -2, 0, 1, 0, -2, -3, -4, -3, -2, 0, 0, 0, 1, 3, 5, \
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7, 8, 9, 8, 8, 8, 9, 9, 9, 8, 8, 6, 2, -3, -9, -15, -18, -17, -14, -10, -6, -2, 0, 1, 2, 2, 0, -1, -1, -2, -1, 0, \
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0, 0, 0, 1, 3, 5, 7, 8, 8, 9, 9, 10, 10, 10, 10, 8, 5, 0, -5, -11, -15, -16, -15, -12, -8, -4, -1, 0, 2, 3, 2, 1, 0, \
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0, 0, 0, 0, -1, -2, -2, -1, 0, 3, 6, 8, 6, 9, 10, 11, 12, 12, 11, 9, 5, 0, -7, -12, -15, -15, -13, -10, -7, -3, \
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0, 1, 2, 3, 3, 3, 2, 1, 0, 0, -1, -3, -4, -5, -5, -2, 0, 3, 6, 5, 8, 11, 13, 15, 15, 14, 11, 5, -1, -9, -14, -17, \
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-16, -14, -11, -7, -3, 0, 1, 3, 4, 5, 5, 5, 4, 3, 1, -1, -4, -7, -8, -8, -6, -2, 1, 5, 4, 8, 12, 15, 17, 18, 16, \
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12, 5, -3, -12, -18, -20, -19, -16, -13, -8, -4, -1, 1, 4, 6, 8, 9, 9, 9, 7, 3, -1, -6, -10, -12, -11, -9, -5, \
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0, 4, 3, 9, 14, 17, 20, 21, 19, 14, 4, -8, -19, -25, -26, -25, -21, -17, -12, -7, -2, 1, 5, 9, 13, 15, 16, 16, \
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13, 7, 0, -7, -12, -15, -14, -11, -6, -1, 3
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};
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static float get_lookup_table_val(unsigned lat, unsigned lon);
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__EXPORT float get_mag_declination(float lat, float lon)
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{
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/*
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* If the values exceed valid ranges, return zero as default
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* as we have no way of knowing what the closest real value
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* would be.
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*/
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if (lat < -90.0f || lat > 90.0f ||
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lon < -180.0f || lon > 180.0f) {
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return 0.0f;
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}
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/* round down to nearest sampling resolution */
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int min_lat = (((int)lat) / SAMPLING_RES) * SAMPLING_RES;
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int min_lon = (((int)lon) / SAMPLING_RES) * SAMPLING_RES;
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/* for the rare case of hitting the bounds exactly
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* the rounding logic wouldn't fit, so enforce it.
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*/
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/* limit to table bounds - required for maxima even when table spans full globe range */
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if (lat <= SAMPLING_MIN_LAT) {
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min_lat = SAMPLING_MIN_LAT;
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}
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if (lat >= SAMPLING_MAX_LAT) {
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min_lat = (((int)lat) / SAMPLING_RES) * SAMPLING_RES - SAMPLING_RES;
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}
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if (lon <= SAMPLING_MIN_LON) {
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min_lon = SAMPLING_MIN_LON;
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}
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if (lon >= SAMPLING_MAX_LON) {
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min_lon = (((int)lon) / SAMPLING_RES) * SAMPLING_RES - SAMPLING_RES;
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}
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/* find index of nearest low sampling point */
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unsigned min_lat_index = (90 + min_lat) / SAMPLING_RES;
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unsigned min_lon_index = (180 + min_lat) / SAMPLING_RES;
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float declination_sw = get_lookup_table_val(min_lat_index, min_lon_index);
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float declination_se = get_lookup_table_val(min_lat_index, min_lon_index + 1);
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float declination_ne = get_lookup_table_val(min_lat_index + 1, min_lon_index + 1);
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float declination_nw = get_lookup_table_val(min_lat_index + 1, min_lon_index);
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/* perform bilinear interpolation on the four grid corners */
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float declination_min = ((lon - min_lon) / SAMPLING_RES) * (declination_se - declination_sw) + declination_sw;
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float declination_max = ((lon - min_lon) / SAMPLING_RES) * (declination_ne - declination_nw) + declination_nw;
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return (lat - min_lat) / SAMPLING_RES * (declination_max - declination_min) + declination_min;
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}
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float get_lookup_table_val(unsigned lat_index, unsigned lon_index)
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{
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return declination_table[lat_index][lon_index];
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}
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@@ -0,0 +1,47 @@
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/****************************************************************************
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*
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* Copyright (c) 2014 MAV GEO Library (MAVGEO). All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
|
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name MAVGEO nor the names of its contributors may be
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* used to endorse or promote products derived from this software
|
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
|
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
|
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
|
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
|
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
|
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
|
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/**
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* @file geo_mag_declination.h
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*
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* Calculation / lookup table for earth magnetic field declination.
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*
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*/
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#pragma once
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__BEGIN_DECLS
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__EXPORT float get_mag_declination(float lat, float lon);
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__END_DECLS
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@@ -35,4 +35,5 @@
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# Geo library
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#
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SRCS = geo.c
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SRCS = geo.c \
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geo_mag_declination.c
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