ImagickDraw::arc

You can do a pie chart with a combination of arc and polygon functions (there really ought to be a built-in command for this)

<?php
//  create a new canvas object and a white image
$canvas     = new Imagick();
$canvas->newImage(600, 600, 'grey');

image_pie($canvas, 300, 300, 200, 0, 45, 'red');
image_pie($canvas, 300, 300, 200, 45, 125, 'green');
image_pie($canvas, 300, 300, 200, 125, 225, 'blue');
image_pie($canvas, 300, 300, 200, 225, 300, 'cyan');
image_pie($canvas, 300, 300, 200, 300, 360, 'orange');

//  output the image
$canvas->setImageFormat('png');
header("Content-Type: image/png");
echo $canvas;
exit;

// FUNCTIONS

function image_arc( &$canvas, $sx, $sy, $ex, $ey, $sd, $ed, $color = 'black' ) {

    //  draw arc on canvas
    //  $sx, $sy, $ex, $ey specify a bounding rectangle of a circle with the origin in the middle
    //  $sd, and $ed specify start and end angles in degrees

    $draw = new ImagickDraw();
    $draw->setFillColor($color);
    $draw->setStrokeColor($color);
    $draw->setStrokeWidth(1);
    $draw->arc($sx, $sy, $ex, $ey, $sd, $ed);
    $canvas->drawImage($draw);
}

function image_pie( &$canvas, $ox, $oy, $radius, $sd, $ed, $color = 'black' ) {

    //  draw pie segment
    //  $ox, $oy specify the circle origin
    //  $sd, and $ed specify start and end angles in degrees
    //  degrees start from 0 = East, and go clockwise

    //  position 1 - convert degrees to radians and get first point on perimeter of circle
    $x1     = $radius * cos($sd / 180 * 3.1416);
    $y1     = $radius * sin($sd / 180 * 3.1416);

    //  position 2 - convert degrees to radians and get second point on perimeter of circle
    $x2     = $radius * cos($ed / 180 * 3.1416);
    $y2     = $radius * sin($ed / 180 * 3.1416);

    //  draw segment triangle - specify the 3 points and draw a polygon
    $points = array(array('x' => $ox, 'y' => $oy), array('x' => $ox + $x1, 'y' => $oy + $y1), array('x' => $ox + $x2, 'y' => $oy + $y2));

    image_polygon($canvas, $points, $color);

    //  draw corrsesponding arc to complete the "pie" segment
    image_arc($canvas, $ox - $radius, $oy - $radius, $ox + $radius, $oy + $radius, $sd, $ed, $color);
}

function image_polygon( &$canvas, $points, $color = 'black' ) {

    //  draw a polygon on canvas

    $draw = new ImagickDraw();
    $draw->setFillColor($color);
    $draw->setStrokeColor($color);
    $draw->setStrokeWidth(1);
    $draw->polygon($points);
    $canvas->drawImage($draw);
}

?>