2 // interpolater.cxx -- routines to handle linear interpolation from a table of
3 // x,y The table must be sorted by "x" in ascending order
5 // Written by Curtis Olson, started April 1998.
7 // Copyright (C) 1998 Curtis L. Olson - http://www.flightgear.org/~curt
9 // This library is free software; you can redistribute it and/or
10 // modify it under the terms of the GNU Library General Public
11 // License as published by the Free Software Foundation; either
12 // version 2 of the License, or (at your option) any later version.
14 // This library is distributed in the hope that it will be useful,
15 // but WITHOUT ANY WARRANTY; without even the implied warranty of
16 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 // Library General Public License for more details.
19 // You should have received a copy of the GNU General Public License
20 // along with this program; if not, write to the Free Software
21 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
26 #include <simgear/compiler.h>
30 #include <simgear/debug/logstream.hxx>
31 #include <simgear/misc/sgstream.hxx>
33 #include "interpolater.hxx"
37 // Constructor -- starts with an empty table.
38 SGInterpTable::SGInterpTable()
43 // Constructor -- loads the interpolation table from the specified
45 SGInterpTable::SGInterpTable( const string& file )
47 SG_LOG( SG_MATH, SG_INFO, "Initializing Interpolator for " << file );
49 sg_gzifstream in( file );
50 if ( !in.is_open() ) {
51 SG_LOG( SG_GENERAL, SG_ALERT, "Cannot open file: " << file );
65 // Add an entry to the table.
66 void SGInterpTable::addEntry (double ind, double dep)
71 // Given an x value, linearly interpolate the y value from the table
72 double SGInterpTable::interpolate(double x) const
78 // Find the table bounds for the requested input.
79 Table::const_iterator upBoundIt = _table.upper_bound(x);
80 // points to a value outside the map. That is we are out of range.
82 if (upBoundIt == _table.end())
83 return _table.rbegin()->second;
85 // points to the first key must be lower
86 // use the first entry
87 if (upBoundIt == _table.begin())
88 return upBoundIt->second;
90 // we know that we do not stand at the beginning, so it is safe to do so
91 Table::const_iterator loBoundIt = upBoundIt;
94 // Just do linear interpolation.
95 double loBound = loBoundIt->first;
96 double upBound = upBoundIt->first;
97 double loVal = loBoundIt->second;
98 double upVal = upBoundIt->second;
100 // division by zero should not happen since the std::map
101 // has sorted out duplicate entries before. Also since we have a
102 // map, we know that we get different first values for different iterators
103 return loVal + (upVal - loVal)*(x - loBound)/(upBound - loBound);
108 SGInterpTable::~SGInterpTable() {