<?php

// Define parameters for the image
	$size = 150; // The height & width of the image 
	$arcwidth = 100; // The number of degrees the arc should span
	$min = 0; // Opacity of the field of view icon at its vertex (0-127 scale, 0=opaque, 127=transparent)
	$max = 127; // Opacity at edge
	$color = array('red'=>0, 'green'=>0, 'blue'=>255);
	
// Start the image
	$image = imageCreate($size, $size);
	
// Set and fill a background color
	$bgColor = imageColorAllocate($image, 0, 192, 192);
	imageFilledRectangle($image, 0, 0, $size - 1, $size - 1, $bgColor);
	
// Set blending type
	imageAlphaBlending($image, 0);
	
// Define other arc-related parameters	
	$startdeg = $_GET['yaw']-90-($arcwidth/2);
	$enddeg = $startdeg+$arcwidth;
	$increment = ($max - $min) / ($size-1); // Incremental change in opacity for each arc drawn		
	
// This draws (size-1) arcs, each being 1 pixel smaller and 1 increment of opacity less than the previous
// i.e. The first arc drawn is (size-1)px with (max) opacity, and the last arc is 1px with (min) opacity

	for($i=$size-1; $i>0; $i--){
		$settings = imageColorAllocateAlpha($image, $color['red'], $color['green'], $color['blue'], $max-($increment*($size-$i)));
		imageFilledArc($image, $size/2, $size/2, $i, $i, $startdeg, $enddeg, $settings, gdArc);
	}
	
// Set content type
	header("Content-type:  image/png");
	
// Interlaced image
	imageInterlace($image, 1);
	
// Set background color to be transparent
	imageColorTransparent($image, $bgColor);
	
// Finalize & send image
	imagePNG($image);
	
?>