113 lines
2.8 KiB
C++
113 lines
2.8 KiB
C++
//
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// interpolater.cxx -- routines to handle linear interpolation from a table of
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// x,y The table must be sorted by "x" in ascending order
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//
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// Written by Curtis Olson, started April 1998.
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//
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// Copyright (C) 1998 Curtis L. Olson - curt@me.umn.edu
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//
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// This library is free software; you can redistribute it and/or
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// modify it under the terms of the GNU Library General Public
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// License as published by the Free Software Foundation; either
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// version 2 of the License, or (at your option) any later version.
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//
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// Library General Public License for more details.
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//
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// You should have received a copy of the GNU Library General Public
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// License along with this library; if not, write to the
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// Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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// Boston, MA 02111-1307, USA.
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//
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// $Id$
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#include <simgear/compiler.h>
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#include <stdlib.h> // for exit()
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#include STL_STRING
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#include <simgear/fg_zlib.h>
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#include <simgear/debug/logstream.hxx>
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#include <simgear/misc/fgstream.hxx>
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#include "interpolater.hxx"
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SG_USING_STD(string);
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// Constructor -- loads the interpolation table from the specified
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// file
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SGInterpTable::SGInterpTable( const string& file ) {
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FG_LOG( FG_MATH, FG_INFO, "Initializing Interpolator for " << file );
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fg_gzifstream in( file );
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if ( !in.is_open() ) {
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FG_LOG( FG_GENERAL, FG_ALERT, "Cannot open file: " << file );
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exit(-1);
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}
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size = 0;
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in >> skipcomment;
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while ( in ) {
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if ( size < MAX_TABLE_SIZE ) {
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in >> table[size][0] >> table[size][1];
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in >> skipws;
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size++;
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} else {
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FG_LOG( FG_MATH, FG_ALERT,
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"fgInterpolateInit(): Exceed max table size = "
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<< MAX_TABLE_SIZE );
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exit(-1);
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}
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}
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}
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// Given an x value, linearly interpolate the y value from the table
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double SGInterpTable::interpolate(double x) {
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int i;
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double y;
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i = 0;
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while ( (x > table[i][0]) && (i < size) ) {
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// cout << " i = " << i << " table[i][0] = " << table[i][0] << endl;
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// cout << " size = " << size << endl;
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i++;
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}
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// printf ("i = %d ", i);
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if ( (i == 0) && (x < table[0][0]) ) {
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FG_LOG( FG_MATH, FG_DEBUG,
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"interpolate(): lookup error, x to small = " << x );
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return table[0][1];
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}
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// cout << " table[size-1][0] = " << table[size-1][0] << endl;
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if ( x > table[size-1][0] ) {
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FG_LOG( FG_MATH, FG_DEBUG,
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"interpolate(): lookup error, x to big = " << x );
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return table[size-1][1];
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}
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// y = y1 + (y0 - y1)(x - x1) / (x0 - x1)
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y = table[i][1] +
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( (table[i-1][1] - table[i][1]) *
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(x - table[i][0]) ) /
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(table[i-1][0] - table[i][0]);
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return(y);
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}
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// Destructor
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SGInterpTable::~SGInterpTable( void ) {
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}
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