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https://github.com/tumic0/GPXSee.git
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59 lines
1.4 KiB
C++
59 lines
1.4 KiB
C++
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#include <QtEndian>
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#include "common/coordinates.h"
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#include "dem.h"
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#define SRTM3_SAMPLES 1201
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#define SRTM1_SAMPLES 3601
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#define SRTM_SIZE(samples) \
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((samples) * (samples) * 2)
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static qreal height(const Coordinates &c, const QByteArray data)
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{
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int samples;
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if (data.size() == SRTM_SIZE(SRTM3_SAMPLES))
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samples = SRTM3_SAMPLES;
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else if (data.size() == SRTM_SIZE(SRTM1_SAMPLES))
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samples = SRTM1_SAMPLES;
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else
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return NAN;
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int lat = int(qRound((c.lat() - int(c.lat())) * (samples - 1)));
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int lon = int(qRound((c.lon() - int(c.lon())) * (samples - 1)));
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int pos = ((samples - 1 - lat) * samples + lon) * 2;
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qint16 val = qFromBigEndian(*((const qint16*)(data.constData() + pos)));
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return (val == -32768) ? NAN : val;
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}
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QString DEM::fileName(const Key &key) const
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{
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const char ns = (key.lat >= 0) ? 'N' : 'S';
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const char ew = (key.lon >= 0) ? 'E' : 'W';
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QString basename = QString("%1%2%3%4.hgt").arg(ns)
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.arg(qAbs(key.lat), 2, 10, QChar('0')).arg(ew)
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.arg(qAbs(key.lon), 3, 10, QChar('0'));
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return _dir.absoluteFilePath(basename);
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}
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qreal DEM::elevation(const Coordinates &c)
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{
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Key k((int)c.lon(), (int)c.lat());
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QMap<Key, QByteArray>::const_iterator it(_data.find(k));
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if (it == _data.constEnd()) {
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QFile file(fileName(k));
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if (!file.open(QIODevice::ReadOnly))
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return NAN;
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else {
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it = _data.insert(k, file.readAll());
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return height(c, *it);
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}
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} else
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return height(c, *it);
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}
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