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.
24 // (Log is kept at end of this file)
29 #include <Debug/fg_debug.h>
30 #include <zlib/zlib.h>
32 #include "interpolater.hxx"
35 // Constructor -- loads the interpolation table from the specified
37 fgINTERPTABLE::fgINTERPTABLE( char *file ) {
38 char gzfile[256], line[256];
41 fgPrintf( FG_MATH, FG_INFO, "Initializing Interpolator for %s\n", file);
43 // First try "file.gz"
45 strcat(gzfile, ".gz");
46 if ( (fd = gzopen(gzfile, "r")) == NULL ) {
48 if ( (fd = gzopen(file, "r")) == NULL ) {
49 fgPrintf(FG_MATH, FG_EXIT, "Cannot open file: %s\n", file);
54 while ( gzgets(fd, line, 250) != NULL ) {
55 if ( size < MAX_TABLE_SIZE ) {
56 sscanf(line, "%lf %lf\n", &(table[size][0]), &(table[size][1]));
59 fgPrintf( FG_MATH, FG_EXIT,
60 "fgInterpolateInit(): Exceed max table size = %d\n",
69 // Given an x value, linearly interpolate the y value from the table
70 double fgINTERPTABLE::interpolate(double x) {
76 while ( (x > table[i][0]) && (i < size) ) {
80 // printf ("i = %d ", i);
82 if ( (i == 0) && (x < table[0][0]) ) {
83 fgPrintf( FG_MATH, FG_ALERT,
84 "fgInterpolateInit(): lookup error, x to small = %.2f\n", x);
88 if ( x > table[i][0] ) {
89 fgPrintf( FG_MATH, FG_ALERT,
90 "fgInterpolateInit(): lookup error, x to big = %.2f\n", x);
94 // y = y1 + (y0 - y1)(x - x1) / (x0 - x1)
96 ( (table[i-1][1] - table[i][1]) *
98 (table[i-1][0] - table[i][0]);
105 fgINTERPTABLE::~fgINTERPTABLE( void ) {
110 // Revision 1.2 1998/04/22 13:18:10 curt
111 // C++ - ified comments. Make file open errors fatal.
113 // Revision 1.1 1998/04/21 19:14:23 curt
115 // Makefile.am Makefile.in
117 // interpolater.cxx interpolater.hxx