Outline a bitmap in Inkscape

I keep doing this for lasercuts but getting a double outline instead of a single outline, and so a double cut. This is because (apparently) Inkscape doesn’t do “centre line tracing”. For simple shapes there’s a work-around though:

• paste the bitmap into a document
• Path -> trace bitmap, inverting the image
• Delete the image, select the trace
• Path-> stroke to path
• delete the square outline of the image

I’ve put a video of this on flickr.