#include <stdio.h>
#include <math.h>
#include <stdlib.h>

#define MAXR 300 
#define MAXTHETA 360


/*
 cc -o lookat lookat.c -lm
 lookat KIWA.vol140.dat

 This little gem of a program reads in KIWA.vol140.dat
 and demonstrates how to convert an (x,y) coordinate to an (r,theta)
 coordinate, and to then grab the data value from val(r,theta).
 The students task is to convert this program to one that outputs
 a .ppm image file of the radar data. */  

main(int argc, char *argv[])
{
  FILE *ifp,*ofp;
  float val[MAXR][MAXTHETA];
  float x,y,r,th,pi,rad,v;
  char firstline[200];
  int i,j,red,green,blue,ri,thi;

  pi=4*atan2(1.,1.);
  rad=180./pi;

  printf("will try to read %s\n",argv[1]);
  ifp=fopen(argv[1],"r");
  fgets(firstline,200,ifp);
  for (ri=0; ri<MAXR; ri++)  {
    for (thi=0; thi<MAXTHETA; thi++)  {
      fscanf(ifp,"%f",&val[ri][thi]);
    }
  }
  fclose(ifp);
  ofp=fopen("output.dat","w");
  fprintf(ofp,"P3\n# radar output file\n420 420\n255\n");
  for (j=-210; j<210; j++)
    {
    for (i=-210; i<210; i++)
      {
      r=sqrt(i*i+j*j);
      th=atan2(j,i)*rad;
      th=th+360.;
      thi=floor(th);
      thi=thi+90.;
      thi=thi % 360;
      ri=floor(r);
      v=val[ri][thi];
      red=floor(v*255./51.);
      blue=floor(255-red);
      green=0;
      if (v<0)
        {
        red=0;
        green=0;
        blue=0;
        }
      if ((red>255) || (blue>255) || (green>255))
        {
        printf("Value exceeds max");
        }
      fprintf(ofp,"%d %d %d\n",red,green,blue);
      }
    } 
}