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spline6.c
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// /ngslib/source/Clib_billw/SCCS/s.spline6.c
// ----- constants ---------------------------------------------------
static const char SCCSID[]="$Id: spline6.c 50355 2010-10-19 15:55:47Z Srinivas.Reddy $";
static const int DEBUG = 0; // diagnostics print if != 0
// ----- standard library --------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h> // floor
// ----- classes, structs, types -------------------------------------
#include "grid_header.h"
typedef struct {
float ff;
} BUFFER;
// ----- functions ---------------------------------------------------
#include "spline6.h"
#include "spline.h"
#include "initsp.h"
#include "flip_endian_f.h"
double spline6(double latdd, double londd,
FILE* vec_ifp[50], GRID_HEADER vec_hdr[50], int kk) {
/*******************************************************************************
* Spline interpolation using a 6x6 window around the given point(latdd, londd)
* The size of the window can be changed to any even number.
* Odd numbers are excluded since their use leads to non-symmetry
* in the distribution of data arount the interpolation point.
* Point in question must be inside of the outermost two data rings.
* if( irown >= 3 && irown < (latRowNum - 2)
* && icoln >= 3 && icoln < (lonColNum - 2) ) {
* val = spline6(xlat, xlon, vec_ifp, vec_hdr, kk);
*
* in - latdd : North lat of point in question units = decdeg
* in - londd : East lon of point in question units = decdeg
* in - lin : vector of file unit numbers, pointing to grid files
* Data files must be direct access.
* in - kk : unit number of geoid grid data file
* out- interp : interpolated geoid height, units as per data file
*******************************************************************************/
FILE* infile;
BUFFER buffer;
const int nn = 6; // size of interpolation window
double latMin; // header record data
double lonMin;
double latDelta;
double lonDelta;
long latRowNum;
long lonColNum;
long iKind;
double latMax; // calcd from header data
double lonMax; // calcd from header data
long irown;
long icoln;
double irown_lat;
double icoln_lon;
double row_counter;
double col_counter;
float xx;
float yy;
long irec; // binary data file element
double interp; // the interpolated geoid value
float f1, f2, f3, f4, f5, f6;
float f7, f8, f9, f10, f11, f12;
float f13, f14, f15, f16, f17, f18;
float f19, f20, f21, f22, f23, f24;
float f25, f26, f27, f28, f29, f30;
float f31, f32, f33, f34, f35, f36;
double AA[6];
double RR[6];
double QQ[6];
double HC[6];
// ---------------------------------------------------------------
// Define some necessary parameters
// These header data elements are read in the main driver file,
// are in a common block, and are already checked for endian condition
// ---------------------------------------------------------------
latMin = vec_hdr[kk].lat_min;
lonMin = vec_hdr[kk].lon_min;
latDelta = vec_hdr[kk].lat_delta;
lonDelta = vec_hdr[kk].lon_delta;
latRowNum = vec_hdr[kk].lat_num;
lonColNum = vec_hdr[kk].lon_num;
iKind = vec_hdr[kk].ikind;
latMax = latMin + latDelta * (latRowNum - 1);
lonMax = lonMin + lonDelta * (lonColNum - 1);
infile = vec_ifp[kk];
if (DEBUG > 0) {
fprintf(stderr, "\
latMin = %lf\n\
lonMin = %lf\n\
latDelta = %lf\n\
lonDelta = %lf\n\
latRowNum = %ld\n\
lonColNum = %ld\n\
iKind = %ld\n\
latMax = %lf\n\
lonMax = %lf\n",
latMin, lonMin, latDelta, lonDelta, latRowNum, lonColNum,
iKind, latMax, lonMax);
}
// --------------------------------------------------------------------
// Find the row/col of the nearest grid node to the lat/lon point
// This grid node is southwest from the lat/lon point
// (Row_counter,Col_counter) = exact (lat,lon) grid coord location (real*8)
// (Row,Col) = closest node (to sw) grid coord loc'n (int)
// --------------------------------------------------------------------
row_counter = ((latdd-latMin) / latDelta);
col_counter = ((londd-lonMin) / lonDelta);
// Find the reference node row and col
irown = (long)floor(row_counter); // the row just south from latdd
icoln = (long)floor(col_counter); // the col just west from londd
// Find the latitude and longitude of the reference node
irown_lat = latMin + latDelta*(irown); // lat just south(up) from latdd
icoln_lon = lonMin + lonDelta*(icoln); // lon just west(left) from londd
// Find relative location of the point in the interpolation window
yy = (row_counter - irown) + 3.0; // 3 := 6x6 spline window
xx = (col_counter - icoln) + 3.0;
if (DEBUG > 0) {
fprintf(stderr, "\
In function spline6: \n\
kk = %d \n\
latdd = %lf\n\
londd = %lf\n\
row_counter = %lf\n\
col_counter = %lf\n\
irown = %ld\n\
icoln = %ld\n\
xx = %lf\n\
yy = %lf\n\
irown_lat = %lf\n\
(Nlat) should be: irown_lat < latdd \n\
icoln_lon = %lf\n\
(Elon) should be: icoln_lon < londd \n",
kk, latdd, londd,
row_counter, col_counter, irown, icoln, xx, yy,
latdd, londd, irown_lat, icoln_lon);
}
// ---------------------------------------------------------------
// At this point, the (irown,icoln) coordinate pair represent
// that grid node which is south and west from the lat/lon point,
// about which we must get a 4x4 data matrix for spline interpolation
// Extract 6x6 array and use it for the spline interpolation
// 44L gets past the header
// irown*lonColNum gets to the row
// icoln gets the data from the specific column
//
// The fread positions the seek pointer after the read value,
// so subsequent freads already have the seek pointer correctly set.
// ---------------------------------------------------------------
irec = 44L + (long)(4*( (irown-2)*lonColNum + (icoln-2) ));
fseek(infile, irec, SEEK_SET);
fread((char*)&buffer, (sizeof(float)), 1, infile); // icoln-2
f1 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile); // icoln-1
f2 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile); // icoln
f3 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile); // icoln+1
f4 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile); // icoln+2
f5 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile); // icoln+3
f6 = buffer.ff;
irec = 44L + (long)(4*( (irown-1)*lonColNum + (icoln-2) ));
fseek(infile, irec, SEEK_SET);
fread((char*)&buffer, (sizeof(float)), 1, infile);
f7 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f8 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f9 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f10 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f11 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f12 = buffer.ff;
irec = 44L + (long)(4*( (irown )*lonColNum + (icoln-2) ));
fseek(infile, irec, SEEK_SET);
fread((char*)&buffer, (sizeof(float)), 1, infile);
f13 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f14 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f15 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f16 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f17 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f18 = buffer.ff;
irec = 44L + (long)(4*( (irown+1)*lonColNum + (icoln-2) ));
fseek(infile, irec, SEEK_SET);
fread((char*)&buffer, (sizeof(float)), 1, infile);
f19 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f20 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f21 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f22 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f23 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f24 = buffer.ff;
irec = 44L + (long)(4*( (irown+2)*lonColNum + (icoln-2) ));
fseek(infile, irec, SEEK_SET);
fread((char*)&buffer, (sizeof(float)), 1, infile);
f25 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f26 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f27 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f28 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f29 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f30 = buffer.ff;
irec = 44L + (long)(4*( (irown+3)*lonColNum + (icoln-2) ));
fseek(infile, irec, SEEK_SET);
fread((char*)&buffer, (sizeof(float)), 1, infile);
f31 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f32 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f33 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f34 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f35 = buffer.ff;
fread((char*)&buffer, (sizeof(float)), 1, infile);
f36 = buffer.ff;
// Convert big endian values to little endian
if (vec_hdr[kk].ikind != 1) {
f1 = flip_endian_f( f1 );
f2 = flip_endian_f( f2 );
f3 = flip_endian_f( f3 );
f4 = flip_endian_f( f4 );
f5 = flip_endian_f( f5 );
f6 = flip_endian_f( f6 );
f7 = flip_endian_f( f7 );
f8 = flip_endian_f( f8 );
f9 = flip_endian_f( f9 );
f10 = flip_endian_f( f10 );
f11 = flip_endian_f( f11 );
f12 = flip_endian_f( f12 );
f13 = flip_endian_f( f13 );
f14 = flip_endian_f( f14 );
f15 = flip_endian_f( f15 );
f16 = flip_endian_f( f16 );
f17 = flip_endian_f( f17 );
f18 = flip_endian_f( f18 );
f19 = flip_endian_f( f19 );
f20 = flip_endian_f( f20 );
f21 = flip_endian_f( f21 );
f22 = flip_endian_f( f22 );
f23 = flip_endian_f( f23 );
f24 = flip_endian_f( f24 );
f25 = flip_endian_f( f25 );
f26 = flip_endian_f( f26 );
f27 = flip_endian_f( f27 );
f28 = flip_endian_f( f28 );
f29 = flip_endian_f( f29 );
f30 = flip_endian_f( f30 );
f31 = flip_endian_f( f31 );
f32 = flip_endian_f( f32 );
f33 = flip_endian_f( f33 );
f34 = flip_endian_f( f34 );
f35 = flip_endian_f( f35 );
f36 = flip_endian_f( f36 );
}
if (DEBUG > 0) {
fprintf(stderr, "\n\
Grid data view (north is down, east to the right, zero offset numbering)\n\
%3ld %f %f %f | %f %f %f \n\
%3ld %f %f %f | %f %f %f \n\
%3ld %f %f %f | %f %f %f \n\
------------------------------------------------------------------------- \n\
%3ld %f %f %f | %f %f %f \n\
%3ld %f %f %f | %f %f %f \n\
%3ld %f %f %f | %f %f %f \n\
%ld %ld %ld %ld %ld %ld\n",
irown-2, f1, f2, f3, f4, f5, f6,
irown-1, f7, f8, f9, f10, f11, f12,
irown , f13, f14, f15, f16, f17, f18,
irown+1, f19, f20, f21, f22, f23, f24,
irown+2, f25, f26, f27, f28, f29, f30,
irown+3, f31, f32, f33, f34, f35, f36,
icoln-2, icoln-1, icoln, icoln+1, icoln+2, icoln+3);
}
AA[0] = f1;
AA[1] = f2;
AA[2] = f3;
AA[3] = f4;
AA[4] = f5;
AA[5] = f6;
initsp(AA,nn,RR,QQ);
HC[0] = spline (xx,AA,nn,RR);
if (DEBUG > 0) { printf("HC[0] = %12.8lf\n", HC[0]); }
AA[0] = f7;
AA[1] = f8;
AA[2] = f9;
AA[3] = f10;
AA[4] = f11;
AA[5] = f12;
initsp(AA,nn,RR,QQ);
HC[1] = spline (xx,AA,nn,RR);
if (DEBUG > 0) { printf("HC[1] = %12.8lf\n", HC[1]); }
AA[0] = f13;
AA[1] = f14;
AA[2] = f15;
AA[3] = f16;
AA[4] = f17;
AA[5] = f18;
initsp(AA,nn,RR,QQ);
HC[2] = spline (xx,AA,nn,RR);
if (DEBUG > 0) { printf("HC[2] = %12.8lf\n", HC[2]); }
AA[0] = f19;
AA[1] = f20;
AA[2] = f21;
AA[3] = f22;
AA[4] = f23;
AA[5] = f24;
initsp(AA,nn,RR,QQ);
HC[3] = spline (xx,AA,nn,RR);
if (DEBUG > 0) { printf("HC[3] = %12.8lf\n", HC[3]); }
AA[0] = f25;
AA[1] = f26;
AA[2] = f27;
AA[3] = f28;
AA[4] = f29;
AA[5] = f30;
initsp(AA,nn,RR,QQ);
HC[4] = spline (xx,AA,nn,RR);
if (DEBUG > 0) { printf("HC[4] = %12.8lf\n", HC[4]); }
AA[0] = f31;
AA[1] = f32;
AA[2] = f33;
AA[3] = f34;
AA[4] = f35;
AA[5] = f36;
initsp(AA,nn,RR,QQ);
HC[5] = spline (xx,AA,nn,RR);
if (DEBUG > 0) { printf("HC[5] = %12.8lf\n", HC[5]); }
// variable interp is the spline interpolated value, returned by reference
initsp(HC, nn, RR, QQ);
interp = spline(yy, HC, nn, RR);
if (DEBUG > 0) { printf("interp = %12.8lf\n", interp); }
return( interp );
}//~spline6