>
        <td>midpoint of the arc given as a two element vector [ax, ay] [grid points]</td>
    </tr>

    <tr valign="top">
        <td width = "150"><code>radius</code></td>
        <td>radius of curvature of the arc [grid points]</td>
    </tr>
    
    <tr valign="top">
        <td width = "150"><code>diameter</code></td>
        <td>aperture diameter (length of line connecting arc endpoints) [grid points] </td>
    </tr>
    
	<tr valign="top">
        <td width = "150"><code>focus_pos</code></td>
    