#!F-adobe-helvetica-medium-r-normal--18*
#!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* /usr/lpp/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