127 lines
3.6 KiB
C++
127 lines
3.6 KiB
C++
//
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// interpolater.cxx -- routines to handle linear interpolation from a table of
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// x,y The table must be sorted by "x" in ascending order
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//
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// Written by Curtis Olson, started April 1998.
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//
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// Copyright (C) 1998 Curtis L. Olson - http://www.flightgear.org/~curt
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//
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// This library is free software; you can redistribute it and/or
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// modify it under the terms of the GNU Library General Public
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// License as published by the Free Software Foundation; either
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// version 2 of the License, or (at your option) any later version.
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//
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// Library General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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//
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// $Id$
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#ifdef HAVE_CONFIG_H
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# include <simgear_config.h>
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#endif
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#include <simgear/compiler.h>
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#include <string>
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#include <simgear/debug/logstream.hxx>
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#include <simgear/misc/sgstream.hxx>
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#include <simgear/props/props.hxx>
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#include "interpolater.hxx"
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#include <simgear/math/SGMath.hxx>
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using std::string;
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// Constructor -- starts with an empty table.
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SGInterpTable::SGInterpTable()
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{
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}
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SGInterpTable::SGInterpTable(const SGPropertyNode* interpolation)
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{
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if (!interpolation)
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return;
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std::vector<SGPropertyNode_ptr> entries = interpolation->getChildren("entry");
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for (unsigned i = 0; i < entries.size(); ++i)
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addEntry(entries[i]->getDoubleValue("ind", 0.0),
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entries[i]->getDoubleValue("dep", 0.0));
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}
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// Constructor -- loads the interpolation table from the specified
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// file
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SGInterpTable::SGInterpTable( const string& file )
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{
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SG_LOG( SG_MATH, SG_INFO, "Initializing Interpolator for " << file );
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sg_gzifstream in( file );
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if ( !in.is_open() ) {
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SG_LOG( SG_GENERAL, SG_ALERT, "Cannot open file: " << file );
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return;
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}
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in >> skipcomment;
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while ( in ) {
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double ind, dep;
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in >> ind >> dep;
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in >> skipws;
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_table[ind] = dep;
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}
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}
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// Add an entry to the table.
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void SGInterpTable::addEntry (double ind, double dep)
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{
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_table[ind] = dep;
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}
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// Given an x value, linearly interpolate the y value from the table
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double SGInterpTable::interpolate(double x) const
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{
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// Empty table??
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if (_table.empty())
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return 0;
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// Find the table bounds for the requested input.
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Table::const_iterator upBoundIt = _table.upper_bound(x);
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// points to a value outside the map. That is we are out of range.
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// use the last entry
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if (upBoundIt == _table.end())
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return _table.rbegin()->second;
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// points to the first key must be lower
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// use the first entry
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if (upBoundIt == _table.begin())
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return upBoundIt->second;
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// we know that we do not stand at the beginning, so it is safe to do so
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Table::const_iterator loBoundIt = upBoundIt;
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--loBoundIt;
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// Just do linear interpolation.
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double loBound = loBoundIt->first;
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double upBound = upBoundIt->first;
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double loVal = loBoundIt->second;
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double upVal = upBoundIt->second;
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// division by zero should not happen since the std::map
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// has sorted out duplicate entries before. Also since we have a
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// map, we know that we get different first values for different iterators
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return loVal + (upVal - loVal)*(x - loBound)/(upBound - loBound);
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}
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// Destructor
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SGInterpTable::~SGInterpTable() {
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}
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