87 lines
2.2 KiB
C++
87 lines
2.2 KiB
C++
/*
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* Copyright 2013 Daniel Warner <contact@danrw.com>
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "Observer.h"
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#include "CoordTopocentric.h"
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namespace libsgp4
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{
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/*
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* calculate lookangle between the observer and the passed in Eci object
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*/
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CoordTopocentric Observer::GetLookAngle(const Eci &eci)
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{
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/*
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* update the observers Eci to match the time of the Eci passed in
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* if necessary
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*/
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Update(eci.GetDateTime());
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/*
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* calculate differences
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*/
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Vector range_rate = eci.Velocity() - m_eci.Velocity();
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Vector range = eci.Position() - m_eci.Position();
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range.w = range.Magnitude();
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/*
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* Calculate Local Mean Sidereal Time for observers longitude
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*/
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double theta = eci.GetDateTime().ToLocalMeanSiderealTime(m_geo.longitude);
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double sin_lat = sin(m_geo.latitude);
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double cos_lat = cos(m_geo.latitude);
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double sin_theta = sin(theta);
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double cos_theta = cos(theta);
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double top_s = sin_lat * cos_theta * range.x
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+ sin_lat * sin_theta * range.y - cos_lat * range.z;
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double top_e = -sin_theta * range.x
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+ cos_theta * range.y;
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double top_z = cos_lat * cos_theta * range.x
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+ cos_lat * sin_theta * range.y + sin_lat * range.z;
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double az = atan(-top_e / top_s);
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if (top_s > 0.0)
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{
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az += kPI;
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}
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if (az < 0.0)
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{
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az += 2.0 * kPI;
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}
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double el = asin(top_z / range.w);
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double rate = range.Dot(range_rate) / range.w;
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/*
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* azimuth in radians
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* elevation in radians
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* range in km
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* range rate in km/s
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*/
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return CoordTopocentric(az,
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el,
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range.w,
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rate);
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}
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} // namespace libsgp4
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