Function:      interpol

Purpose:       Get 2d-bilinear interpolated image value at given position
               in a 2-dim array.
               
Category:      MATH

File:          interpol.c

Author:        M. Vogelaar 


Use:           float interpol( float   x,
                               float   y,
                               float **image,
                               fint   *blo,
                               fint   *bhi,
                               float   blank );
                               
               interpol: Output of bilenear interpolated image value
               x, y    : Input of position in image (in grids)
               image   : Input of two dimensional array
               blo     : Input of lower array boundary in x and y in grids
               bhi     : Input of upper array boundary in x and y in grids
               blank   : Input of the value of a GIPSY blank (float)
 
               
               See also function comment in 'interpol.c'
                 
                
Example:       ........
               setfblank_c( &blank );
               image = fmatrix( blo[0], blo[1], bhi[0], bhi[1] );
               gdsi_read_c( Setin, &cwlo, &cwhi, &image[blo[1]][blo[1]],
                            &imagesize, &pixelsread, &tid );
                            
               --- Get the bilinear interpolated value at position -3, -4 ---
               
               bival = interpol( -3, -4, image, blo, bhi, blank );


Comment:       This routine is NOT callable from FORTRAN.


Notes:         The value of a blank is needed to speed up the routine
               by avoiding setting the blank value in the routine itself.

               
Updates:       27 Jul,  2000: VOG, Document created.