[Sommaire] [Imprimer]

   1  <?php
   2  include  ("../jpgraph.php");
   3  include  ("../jpgraph_scatter.php");
   4  
   5  $polex = 6;
   6  $poley = 40;
   7  
   8  function FldCallback($x,$y,$a) {
   9      GLOBAL $polex, $poley;
  10      $maxr = 3000;
  11  
  12      // Size and arrow size is constant
  13      $size="";
  14      $arrowsize="";
  15  
  16      // Since we have different scales we need the data points
  17      // to be of the same magnitude to give it a distance
  18      // interpretation.
  19      $x *= 10; 
  20  
  21      // Colors gets colder the further out we go from the center
  22      $r = ($x-$polex*10)*($x-$polex*10)+($y-$poley)*($y-$poley);
  23      $f = $r/$maxr;
  24      if( $f > 1 ) $f=1;
  25      $red = floor((1-$f)*255);
  26      $blue = floor($f*255);
  27      $color = array($red,0,$blue);
  28      //echo "x=$x, y=$y, blue=$blue, red=$red<br>";
  29      return array($color,$size,$arrowsize);
  30  }
  31  
  32  // Create data for a simulated pseudo-magnetic radient field
  33  $datax = array();
  34  $datay = array();
  35  $angle = array();
  36  for($x=1; $x < 10; ++$x ) {
  37      for($y=10; $y<100; $y += 10) {
  38      $a = -1;
  39      if( $x==$polex && $y==$poley ) continue;
  40      if( $x==$polex ) {
  41          if( $y > $poley ) $a=90;
  42          else $a = 270;
  43      }
  44      if( $y==$poley ) {
  45          if( $x  > $polex ) $a=0;
  46          else  $a=180;        
  47      }
  48      if( $a == -1 ) {
  49          $d1 = $y-$poley;
  50          $d2 = ($polex-$x)*20;
  51          if( $y < $poley ) $d2 *= -1;
  52          $h = sqrt($d1*$d1+$d2*$d2);
  53          $t = -$d2/$h;
  54          $ac = acos($t);
  55          if( $y < $poley ) $ac += M_PI;
  56          $a = $ac * 180/M_PI;
  57      }
  58      $datax[] = $x;
  59      $datay[] = $y;
  60      $angle[] = $a;
  61      }
  62  }
  63  
  64  // Setup the graph
  65  $graph = new Graph(300,200);
  66  $graph->SetScale("intlin",0,100,0,10);
  67  $graph->SetMarginColor('lightblue');
  68  
  69  
  70  // ..and titles
  71  $graph->title->Set("Field plot");
  72  
  73  // Setup the field plot
  74  $fp = new FieldPlot($datay,$datax,$angle);
  75  
  76  // Setup formatting callback
  77  $fp->SetCallback('FldCallback');
  78  
  79  // First size argument is length (in pixels of arrow) 
  80  // Second size argument is roughly size of arrow. Arrow size is specified as
  81  // an integer in the range [0,9]
  82  $fp->arrow->SetSize(20,2);
  83  $fp->arrow->SetColor('navy');
  84  
  85  $graph->Add($fp);
  86  
  87  // .. and output
  88  $graph->Stroke();
  89  
  90  ?>
  91  
  92