title: SVG marker scale only one dimension with stroke width
body: <p>I have SVG lines of variable thickness, and all of them have a marker in the form of an arrow at the end, like in this <a href="http://jsfiddle.net/8uxqK/306/" rel="nofollow noreferrer">fiddle</a>. Per default, <code>markerUnits</code> is set to <code>strokeWidth</code>, which scales both (!) dimensions of the arrow according to the stroke width of the line. </p>
  
  <p>I, on the other hand, would like to only scale the y dimension, as depicted in the very beautiful paint drawing below (should behave like the orange arrows, the red is not what I want).</p>
  
  <p><img src="https://i.stack.imgur.com/xdILu.png" alt="enter image description here"></p>
  
  <p>The reason for this is that I want to model quantities of people moving from one place to another, but the arrows should all have strictly the same length (i.e. line length is not a visual cue, only the stroke width is). </p>
  
  <p>Is there any way to do this "dynamically"; i.e. without recalculating the path of the marker all the time? Is there a library that can do this, e.g. D3? </p>