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#!N 
#!CNavyBlue #!N  #!Rall1036 Writing 
a Filter #!N #!EC #!N #!N The filters used to create 
a Data Explorer format file on disk and on standard output 
are essentially the same. #!N #!N Assume a single data set 
of scalar data stored in an HDF file. All HDF files 
are gridded. The dimensionality and size of the grid are to 
be determined from queries to the data set. #!N #!N The 
following C program requires the HDF file name as an argument. 
It is found in  #!F-adobe-times-bold-r-normal--18*   /opt/local/dx/samples/program_guide/simpleimportfilter.c #!EF . #!CForestGreen #!N #!N 
 #!F-adobe-courier-bold-r-normal--18*   #!N 01 #!N 02 #!N 03 #include <stdio.h> #!EF #!N 
#!N #!EC #!N #!N  #!F-adobe-times-bold-r-normal--18*   df.h #!EF is a necessary include 
file for HDF library routines. #!CForestGreen #!N #!N  #!F-adobe-courier-bold-r-normal--18*   #!N 04 
#include <df.h> #!N 05 #!N 06 #define MAXRANK 3 #!N 07 
#!N 08 main(argc, argv) #!N 09 char *argv[]; #!N 10 { 
#!N 11 FILE *in; #!N 12 char filename[80]; #!N 13 int 
dims, counts[MAXRANK], numelements, i, j; #!N 14 float deltas[MAXRANK*MAXRANK], origins[MAXRANK], *databuf=NULL; 
#!N 15 #!EF #!N #!N #!EC #!N #!N Check that the 
user has supplied the name of the file to be opened. 
#!CForestGreen #!N #!N  #!F-adobe-courier-bold-r-normal--18*   #!N 16 if (argc < 2) { 
#!N 17 fprintf(stderr,"Usage: simpleimportfilter <filename> \n"); #!N 18 return 0; #!N 
19 } #!N 20 #!N 21 strcpy(filename, argv[1]); #!N 22 } 
#!EF #!N #!N #!EC #!N #!N The HDF library routine  #!F-adobe-times-bold-r-normal--18*   
DFishdf #!EF checks the file for accessibility and for the correct 
(HDF) format. If the file is not accessible or is not 
an HDF file, the routine generates an error message. #!CForestGreen #!N 
#!N  #!F-adobe-courier-bold-r-normal--18*   #!N 23 if (DFishdf(filename) != 0) { #!N 24 
fprintf(stderr, #!N 25 "file \"%s\" is not accessible, or is not 
an hdf file\n", #!N 26 filename); #!N 27 return 0; #!N 
28 } #!EF #!N #!N #!EC #!N #!N Initialize the HDF 
library. #!CForestGreen #!N #!N  #!F-adobe-courier-bold-r-normal--18*   #!N 29 DFSDrestart(); #!EF #!N #!N 
#!EC #!N #!N The HDF library routine  #!F-adobe-times-bold-r-normal--18*   DFSDgetdims #!EF returns 
the dimensionality of the grid (1D, 2D, etc.) in  #!F-adobe-times-bold-r-normal--18*   dims 
#!EF . The number of positions in each dimension is returned 
in the Array  #!F-adobe-times-bold-r-normal--18*   counts #!EF . #!CForestGreen #!N #!N  #!F-adobe-courier-bold-r-normal--18*   
#!N 30 DFSDgetdims(filename, &dims, counts, MAXRANK); #!EF #!N #!N #!EC #!N 
#!N Determine the number of elements in the data Array. #!CForestGreen 
#!N #!N  #!F-adobe-courier-bold-r-normal--18*   #!N 31 numelements=1; #!N 32 for (i=0; i<dims; 
i++) { #!N 33 numelements= numelements * counts[i]; #!N 34 } 
#!EF #!N #!N #!EC #!N #!N Create a buffer for the 
data. #!CForestGreen #!N #!N  #!F-adobe-courier-bold-r-normal--18*   #!N 35 databuf = (float *)malloc(numelements*sizeof(float)); 
#!N 36 if (!databuf) { #!N 37 fprintf(stderr,"out of memory\n"); #!N 
38 return 0; #!N 39 } #!EF #!N #!N #!EC #!N 
#!N The HDF library routine  #!F-adobe-times-bold-r-normal--18*   DFSDgetdata #!EF reads the data 
from the HDF file to the data Array. #!CForestGreen #!N #!N 
 #!F-adobe-courier-bold-r-normal--18*   #!N 40 DFSDgetdata(filename, dims, counts, databuf); #!EF #!N #!N #!EC 
#!N #!N Write the Data Explorer file format description of the 
data Array on standard output. #!CForestGreen #!N #!N  #!F-adobe-courier-bold-r-normal--18*   #!N 41 
printf("object 1 class array type float rank 0 items %d data 
follows\n", #!N 42 numelements); #!N 43 for (i=0; i<numelements; i++) #!N 
44 printf(" %f\n ", databuf[i]); #!EF #!N #!N #!EC #!N #!N 
Set the dependency of the data to "positions." #!CForestGreen #!N #!N 
 #!F-adobe-courier-bold-r-normal--18*   #!N 45 printf("attribute \"dep\" string \"positions\"\n "); #!EF #!N #!N 
#!EC #!N #!N Now create the position origin and deltas (origin 
0 and deltas 1 in each dimension). #!CForestGreen #!N #!N  #!F-adobe-courier-bold-r-normal--18*   
#!N 46 for (i=0; i<dims; i++) { #!N 47 origins[i] = 
0.0; #!N 48 for (j=0; j<dims; j++) { #!N 49 if 
(i==j) #!N 50 deltas[i*dims + j] = 1.0; #!N 51 else 
#!N 52 deltas[i*dims + j] = 0.0; #!N 53 } #!N 
54 } #!EF #!N #!N #!EC #!N #!N Write out the 
connections and positions. #!CForestGreen #!N #!N  #!F-adobe-courier-bold-r-normal--18*   #!N 55 switch (dims) 
{ #!N 56 case (1): #!N 57 printf("object 2 class gridconnections 
counts %d\n", counts[0]); #!N 58 printf("object 3 class gridpositions counts %d\n", 
counts[0]); #!N 59 printf(" origin %f\n", origins[0]); #!N 60 printf(" delta 
%f\n", deltas[0]); #!N 61 break; #!N 62 case (2): #!N 63 
printf("object 2 class gridconnections counts %d %d\n", #!N 64 counts[0], counts[1]); 
#!N 65 printf("object 3 class gridpositions counts %d %d\n", #!N 66 
counts[0], counts[1]); #!N 67 printf(" origin %f %f\n", origins[0], origins[1]); #!N 
68 printf(" delta %f %f\n", deltas[0], deltas[1]); #!N 69 printf(" delta 
%f %f\n", deltas[2], deltas[3]); #!N 70 break; #!N 71 case (3): 
#!N 72 printf("object 2 class gridconnections counts %d %d %d\n", #!N 
73 counts[0], counts[1], counts[2]); #!N 74 printf("object 3 class gridpositions counts 
%d %d %d\n", #!N 75 counts[0], counts[1], counts[2]); #!N 76 printf(" 
origin %f %f %f\n", origins[0], origins[1], origins[2]); #!N 77 printf(" delta 
%f %f %f\n", deltas[0], deltas[1], deltas[2]); #!N 78 printf(" delta %f 
%f %f\n", deltas[3], deltas[4], deltas[5]); #!N 79 printf(" delta %f %f 
%f\n", deltas[6], deltas[7], deltas[8]); #!N 80 break; #!N 81 default: #!N 
82 printf(stderr,"dimensionality must be 1D, 2D, or 3D"); #!N 83 return 
0; #!N 84 } #!EF #!N #!N #!EC #!N #!N Write 
out the description of the Field. #!CForestGreen #!N #!N  #!F-adobe-courier-bold-r-normal--18*   #!N 
85 printf("object 4 class field\n"); #!N 86 printf(" component \"data\" value 
1\n"); #!N 87 printf(" component \"connections\" value 2\n"); #!N 88 printf(" 
component \"positions\" value 3\n"); #!N 89 #!N 90 return 1; #!N 
91 #!EF #!N #!N #!EC #!N #!N #!N  #!F-adobe-times-medium-i-normal--18*   Next Topic 
#!EF #!N #!N  #!Lwrimp,dxall1038 h Writing an Import Module  #!EL  #!N  #!F-adobe-times-medium-i-normal--18*   #!N 
