77 lines
2.2 KiB
C
77 lines
2.2 KiB
C
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#include <stdio.h>
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#include <stdlib.h>
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#include "grib2.h"
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int dec_png(unsigned char *,g2int *,g2int *,char *);
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g2int pngunpack(unsigned char *cpack,g2int len,g2int *idrstmpl,g2int ndpts,
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g2float *fld)
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//$$$ SUBPROGRAM DOCUMENTATION BLOCK
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// . . . .
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// SUBPROGRAM: pngunpack
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// PRGMMR: Gilbert ORG: W/NP11 DATE: 2003-08-27
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//
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// ABSTRACT: This subroutine unpacks a data field that was packed into a
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// PNG image format
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// using info from the GRIB2 Data Representation Template 5.41 or 5.40010.
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//
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// PROGRAM HISTORY LOG:
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// 2003-08-27 Gilbert
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//
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// USAGE: pngunpack(unsigned char *cpack,g2int len,g2int *idrstmpl,g2int ndpts,
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// g2float *fld)
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// INPUT ARGUMENT LIST:
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// cpack - The packed data field (character*1 array)
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// len - length of packed field cpack().
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// idrstmpl - Pointer to array of values for Data Representation
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// Template 5.41 or 5.40010
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// ndpts - The number of data values to unpack
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//
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// OUTPUT ARGUMENT LIST:
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// fld[] - Contains the unpacked data values
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//
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// REMARKS: None
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//
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// ATTRIBUTES:
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// LANGUAGE: C
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// MACHINE: IBM SP
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//
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//$$$
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{
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g2int *ifld;
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g2int j,nbits,iret,width,height;
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g2float ref,bscale,dscale;
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unsigned char *ctemp;
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rdieee(idrstmpl+0,&ref,1);
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bscale = int_power(2.0,idrstmpl[1]);
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dscale = int_power(10.0,-idrstmpl[2]);
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nbits = idrstmpl[3];
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//
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// if nbits equals 0, we have a constant field where the reference value
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// is the data value at each gridpoint
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//
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if (nbits != 0) {
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ifld=(g2int *)calloc(ndpts,sizeof(g2int));
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ctemp=(unsigned char *)calloc(ndpts*4,1);
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if ( ifld == 0 || ctemp == 0) {
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fprintf(stderr,"Could not allocate space in jpcunpack.\n Data field NOT upacked.\n");
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return(1);
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}
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iret=(g2int)dec_png(cpack,&width,&height,ctemp);
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gbits(ctemp,ifld,0,nbits,0,ndpts);
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for (j=0;j<ndpts;j++) {
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fld[j]=(((g2float)ifld[j]*bscale)+ref)*dscale;
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}
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free(ctemp);
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free(ifld);
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}
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else {
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for (j=0;j<ndpts;j++) fld[j]=ref;
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}
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return(0);
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}
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