93 lines
2.0 KiB
PHP
93 lines
2.0 KiB
PHP
<?php
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include ("../jpgraph.php");
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include ("../jpgraph_scatter.php");
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$polex = 6;
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$poley = 40;
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function FldCallback($x,$y,$a) {
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GLOBAL $polex, $poley;
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$maxr = 3000;
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// Size and arrow size is constant
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$size="";
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$arrowsize="";
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// Since we have different scales we need the data points
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// to be of the same magnitude to give it a distance
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// interpretation.
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$x *= 10;
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// Colors gets colder the further out we go from the center
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$r = ($x-$polex*10)*($x-$polex*10)+($y-$poley)*($y-$poley);
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$f = $r/$maxr;
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if( $f > 1 ) $f=1;
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$red = floor((1-$f)*255);
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$blue = floor($f*255);
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$color = array($red,0,$blue);
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//echo "x=$x, y=$y, blue=$blue, red=$red<br>";
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return array($color,$size,$arrowsize);
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}
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// Create data for a simulated pseudo-magnetic radient field
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$datax = array();
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$datay = array();
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$angle = array();
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for($x=1; $x < 10; ++$x ) {
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for($y=10; $y<100; $y += 10) {
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$a = -1;
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if( $x==$polex && $y==$poley ) continue;
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if( $x==$polex ) {
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if( $y > $poley ) $a=90;
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else $a = 270;
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}
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if( $y==$poley ) {
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if( $x > $polex ) $a=0;
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else $a=180;
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}
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if( $a == -1 ) {
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$d1 = $y-$poley;
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$d2 = ($polex-$x)*20;
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if( $y < $poley ) $d2 *= -1;
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$h = sqrt($d1*$d1+$d2*$d2);
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$t = -$d2/$h;
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$ac = acos($t);
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if( $y < $poley ) $ac += M_PI;
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$a = $ac * 180/M_PI;
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}
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$datax[] = $x;
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$datay[] = $y;
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$angle[] = $a;
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}
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}
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// Setup the graph
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$graph = new Graph(300,200);
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$graph->SetScale("intlin",0,100,0,10);
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$graph->SetMarginColor('lightblue');
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// ..and titles
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$graph->title->Set("Field plot");
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// Setup the field plot
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$fp = new FieldPlot($datay,$datax,$angle);
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// Setup formatting callback
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$fp->SetCallback('FldCallback');
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// First size argument is length (in pixels of arrow)
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// Second size argument is roughly size of arrow. Arrow size is specified as
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// an integer in the range [0,9]
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$fp->arrow->SetSize(20,2);
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$fp->arrow->SetColor('navy');
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$graph->Add($fp);
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// .. and output
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$graph->Stroke();
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?>
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