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>
28 #include <stdlib.h> // for exit()
32 #include <simgear/debug/logstream.hxx>
33 #include <simgear/misc/sgstream.hxx>
35 #include "interpolater.hxx"
39 // Constructor -- starts with an empty table.
40 SGInterpTable::SGInterpTable()
46 // Constructor -- loads the interpolation table from the specified
48 SGInterpTable::SGInterpTable( const string& file )
51 SG_LOG( SG_MATH, SG_INFO, "Initializing Interpolator for " << file );
53 sg_gzifstream in( file );
54 if ( !in.is_open() ) {
55 SG_LOG( SG_GENERAL, SG_ALERT, "Cannot open file: " << file );
64 table.push_back(Entry(ind, dep));
70 // Add an entry to the table.
71 void SGInterpTable::addEntry (double ind, double dep)
73 table.push_back(Entry(ind,dep));
78 // Given an x value, linearly interpolate the y value from the table
79 double SGInterpTable::interpolate(double x) const
90 while ( (i < size) && (x > table[i].ind) ) {
91 // cout << " i = " << i << " table[i].ind = " << table[i].ind << endl;
92 // cout << " size = " << size << endl;
96 // printf ("i = %d ", i);
99 SG_LOG( SG_MATH, SG_DEBUG,
100 "interpolate(): lookup error, x to small = " << x );
104 // cout << " table[size-1].ind = " << table[size-1].ind << endl;
106 SG_LOG( SG_MATH, SG_DEBUG,
107 "interpolate(): lookup error, x to big = " << x );
108 return table[size-1].dep;
111 // y = y1 + (y0 - y1)(x - x1) / (x0 - x1)
113 ( (table[i-1].dep - table[i].dep) *
114 (x - table[i].ind) ) /
115 (table[i-1].ind - table[i].ind);
122 SGInterpTable::~SGInterpTable() {