src/snark/quad_back.cpp

   1 /*
   2  ***********************************************************
   3  $SNARK_Header: S N A R K  1 4 - A PICTURE RECONSTRUCTION PROGRAM $
   4  $HeadURL: svn://dig.cs.gc.cuny.edu/snark/trunk/src/snark/quad_back.cpp $
   5  $LastChangedRevision: 80 $
   6  $Date: 2014-07-01 21:01:54 -0400 (Tue, 01 Jul 2014) $
   7  $Author: agulati $
   8  ***********************************************************
   9
  10  THE BACK PROJECTIONS ARE STORED IN X AFTER CORRECTION TO AVRDEN
  11  */
  12
  13 #include <cstdio>
  14
  15 #include "blkdta.h"
  16 #include "geom.h"
  17 #include "ray.h"
  18 #include "wray.h"
  19 #include "anglst.h"
  20
  21 #include "quad.h"
  22
  23 void quad_class::back(REAL* x, INTEGER* list, REAL* weight)
  24 {
  25
  26         INTEGER i;
  27         INTEGER np;
  28         REAL dum;   // what is this variable for?? hstau
  29         INTEGER nr;
  30         INTEGER numb;
  31         REAL snorm;
  32         INTEGER nb;
  33         INTEGER ky;
  34         REAL zn;
  35
  36         // ZERO OUT X
  37
  38         for (i = 0; i < GeoPar.area; i++)
  39         {
  40                 x[i] = 0.0;
  41         }
  42
  43         // COMPUTE BACK PROJECTION
  44
  45         if (!GeoPar.strip)
  46         {
  47
  48                 for (np = 0; np < GeoPar.prjnum; np++)
  49                 {
  50                         dum = Anglst.prdta(np, 1);  // should be Anglst.prdta(np, 0)? hstau
  51                         for (nr = 0; nr < GeoPar.nrays; nr++)
  52                         {
  53                                 wray(np, nr, list, weight, &numb, &snorm);
  54                                 if (numb > 0)
  55                                 {
  56                                         for (nb = 0; nb < numb; nb++)
  57                                         {
  58                                                 ky = list[nb];
  59                                                 x[ky] += Anglst.prdta(np, nr) * weight[nb];
  60                                         }
  61                                 }
  62                         }
  63                 }
  64                 zn = (REAL) 1.0 / ((REAL) (GeoPar.prjnum));
  65         }
  66         else
  67         {
  68                 for (np = 0; np < GeoPar.prjnum; np++)
  69                 {
  70                         dum = Anglst.prdta(np, 1);
  71                         for (nr = 0; nr < GeoPar.nrays; nr++)
  72                         {
  73                                 ray(np, nr, list, weight, &numb, &snorm);
  74                                 if (numb > 0)
  75                                 {
  76                                         for (nb = 0; nb < numb; nb++)
  77                                         {
  78                                                 ky = list[nb];
  79                                                 x[ky] += Anglst.prdta(np, nr);
  80                                         }
  81                                 }
  82                         }
  83                 }
  84
  85                 zn = (GeoPar.pixsiz * GeoPar.pixsiz) / ((REAL) (GeoPar.prjnum));
  86
  87                 // CORRECT TO AVRDEN
  88         }
  89
  90         for (i = 0; i < GeoPar.area; i++)
  91         {
  92                 x[i] *= zn;
  93         }
  94
  95         return;
  96 }