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 <simgear/compiler.h>
29 #include <stdlib.h> // for exit()
34 #include <simgear/fg_zlib.h>
35 #include <simgear/debug/logstream.hxx>
36 #include <simgear/misc/fgstream.hxx>
38 #include "interpolater.hxx"
41 // Constructor -- loads the interpolation table from the specified
43 fgINTERPTABLE::fgINTERPTABLE( const string& file ) {
44 FG_LOG( FG_MATH, FG_INFO, "Initializing Interpolator for " << file );
46 fg_gzifstream in( file );
48 FG_LOG( FG_GENERAL, FG_ALERT, "Cannot open file: " << file );
55 if ( size < MAX_TABLE_SIZE ) {
56 in >> table[size][0] >> table[size][1];
59 FG_LOG( FG_MATH, FG_ALERT,
60 "fgInterpolateInit(): Exceed max table size = "
68 // Given an x value, linearly interpolate the y value from the table
69 double fgINTERPTABLE::interpolate(double x) {
75 while ( (x > table[i][0]) && (i < size) ) {
79 // printf ("i = %d ", i);
81 if ( (i == 0) && (x < table[0][0]) ) {
82 FG_LOG( FG_MATH, FG_ALERT,
83 "fgInterpolateInit(): lookup error, x to small = " << x );
87 if ( x > table[i][0] ) {
88 FG_LOG( FG_MATH, FG_ALERT,
89 "fgInterpolateInit(): lookup error, x to big = " << x );
93 // y = y1 + (y0 - y1)(x - x1) / (x0 - x1)
95 ( (table[i-1][1] - table[i][1]) *
97 (table[i-1][0] - table[i][0]);
104 fgINTERPTABLE::~fgINTERPTABLE( void ) {