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 - curt@me.umn.edu
9 // This program is free software; you can redistribute it and/or
10 // modify it under the terms of the GNU General Public License as
11 // published by the Free Software Foundation; either version 2 of the
12 // License, or (at your option) any later version.
14 // This program is distributed in the hope that it will be useful, but
15 // WITHOUT ANY WARRANTY; without even the implied warranty of
16 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 // 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., 675 Mass Ave, Cambridge, MA 02139, USA.
26 #include <Include/compiler.h>
30 #include <Debug/logstream.hxx>
31 #include <Include/fg_zlib.h>
32 #include <Misc/fgstream.hxx>
34 #include "interpolater.hxx"
37 // Constructor -- loads the interpolation table from the specified
39 fgINTERPTABLE::fgINTERPTABLE( const string& file ) {
40 FG_LOG( FG_MATH, FG_INFO, "Initializing Interpolator for " << file );
42 fg_gzifstream in( file );
44 FG_LOG( FG_GENERAL, FG_ALERT, "Cannot open file: " << file );
51 if ( size < MAX_TABLE_SIZE ) {
52 in >> table[size][0] >> table[size][1];
55 FG_LOG( FG_MATH, FG_ALERT,
56 "fgInterpolateInit(): Exceed max table size = "
64 // Given an x value, linearly interpolate the y value from the table
65 double fgINTERPTABLE::interpolate(double x) {
71 while ( (x > table[i][0]) && (i < size) ) {
75 // printf ("i = %d ", i);
77 if ( (i == 0) && (x < table[0][0]) ) {
78 FG_LOG( FG_MATH, FG_ALERT,
79 "fgInterpolateInit(): lookup error, x to small = " << x );
83 if ( x > table[i][0] ) {
84 FG_LOG( FG_MATH, FG_ALERT,
85 "fgInterpolateInit(): lookup error, x to big = " << x );
89 // y = y1 + (y0 - y1)(x - x1) / (x0 - x1)
91 ( (table[i-1][1] - table[i][1]) *
93 (table[i-1][0] - table[i][0]);
100 fgINTERPTABLE::~fgINTERPTABLE( void ) {