Adafruit shows how to accurately design footprints in Eagle. The process imports the mechanical drawing into Eagle, and the footprint is traced over this template. It’s best used for mechanical parts – connectors, buttons, jacks, etc – that have complicated footprint designs.
You can also check out our guide to building simple footprints in Eagle, as well as our other Eagle tutorials.
Nice import to bitmap trick! I’ve actually used these method but instead of using bitmap import I’ve manually draw it to AutoCAD first then extract the coordinates to use and rebuild it to Eagle footprint editor.