I'm using the svg jquery plugin by Keith Wood, not the HTML5 canvas.

I define my svg image like this to scale my svg triangle image to fit its div container:

```html
  <svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="100%" viewBox="0 0 299 215" >
    <g>
    <polygon points="1,1 299,1 149,210" fill="blue" stroke="blue" stroke-width="0" class="votenow"/>
    </g>
    </svg>
```

But how do I then match the coordinate systems?

I want to capture the mouse location at some point over the triangle and draw a circle at those X Y coordinates, but the circle gets drawn in a different location because the coordinate systems don't match.

So a circle would be drawn at point 10,10 but appear to be at 50,60 for example.

How do people cope with this?

Thanks.

Final Solution: Using the JQuery plugin to draw the circle and getScreenCTM() to calculate the points. 

Perhaps I no longer require the JQuery plugin but it will do for now. Couldn't see how to do it using only the plugin.

```
$('#cvtriangle .tri').on( "click", function(e) {
    jqsvg = $('#cvtriangle').svg('get');
    svg = document.querySelector("svg");
    var pt = svg.createSVGPoint();
    pt.x = e.clientX;
    pt.y = e.clientY;
    pt = pt.matrixTransform(svg.getScreenCTM().inverse());
    jqsvg.circle(pt.x, pt.y, 5, {class: 'vote', fill: 'white', stroke: 'white', strokeWidth: 2, cursor: 'pointer'});
});

```