Bilinear and trilinear interpolation library on equidistant and user-supplied grids

Library description

Following functions are provided by < interp.h > :

• 2D bilinear interpolation:
  
  double bilinear_interp (double X, double Y, const double* TABLE,
const int NX, const int NY,
const double X_MIN, const double X_MAX,
const double Y_MIN, const double Y_MAX,
const int OUT_OF_DOMAIN_FLAG, const double OUT_OF_DOMAIN_VALUE );
  
  
• 3D trilinear interpolation:
  
  double trilinear_interp (double X, double Y, double Z, const double* TABLE,
const int NX, const int NY, const NY
const double X_MIN, const double X_MAX,
const double Y_MIN, const double Y_MAX,
const double Z_MIN, const double Z_MAX,
const int OUT_OF_DOMAIN_FLAG, const double OUT_OF_DOMAIN_VALUE );
  
  
• 2D bilinear interpolation on arbitrary grids:
  
  double bilinear_interp_arbitrary_grid (double X, double Y, const double* TABLE,
const double * Xtbl, const int NX,
const double * Ytbl, const int NY,
const int OUT_OF_DOMAIN_FLAG, const double OUT_OF_DOMAIN_VALUE );
  
  
• 3D trilinear interpolation on arbitrary grids:
  
  double trilinear_interp_arbitrary_grid (double X, double Y, double Z, const double* TABLE,
const double * Xtbl, const int NX,
const double * Ytbl, const int NY,
const double * Ztbl, const int NZ,
const int OUT_OF_DOMAIN_FLAG, const double OUT_OF_DOMAIN_VALUE );
  

Download

• Most recent version
• libinterp-0.12.tar.gz , first version, 2012-08-04.

Installation

wget https://th.if.uj.edu.pl/~odrzywolek/homepage/codes/libinterp/source/libinterp-0.12.tar.gz
tar -xvf libinterp-0.12.tar.gz
cd libinterp-0.12
./configure
make
sudo make install


./configure --prefix=$HOME CC=icc
make
make install


Example of use

Go to doc/ directory where you can find example2d.c file:


#include <interp.h>
#include <stdio.h>
#include <math.h>

int main()
{
/* Example 3x3 equidistant grid.

 1---0---1
 |   |   |
 1---2---3
 |   |   |
-1---1---1

*/
const double dat[3][3] = {{-1.0,1.0,1.0},{1.0,2.0,0.0},{1.0,3.0,1.0}};
double x, y;
double f;
int i,j;
for(i=-20;i<=20;i++)
for(j=-20;j<=20;j++)
{
x=0.1*i;
y=0.1*j;
f = bilinear_interp(x,y,dat,3,3,-1.0,1.0,-1.0,1.0,0,0.0);
printf("%lf\t%lf\t%lf\n",x,y,f);
}
return 0;
}


gcc example2d.c -o example2d -linterp

./example2d >test2d.dat

You should get something like this:

Documentation

TODO

Known bugs

Function bilinear_interp on regular grids sometimes selects WRONG (neighbouring one) data point, especially if the values are very close to grid boundaries. This is probably due to round-off errors and suspicious use of ceil function from < math.h > . Interpolation is contiunuous, so this should not lead to catastrophic errors.

Last modified 2012-08-07 17:23