I've done it various different ways - hand-operated touch probes, automatic touchprobes with piezo-electric needle probe, laser scanners, infra-red, and structured light scanners, using various kinds of software. There are lots of ways to get from physical objects to digital ones. But you'd need to specify how much resolution, detail and accuracy you need, what tolerances you can accept. (and what you can afford) before I could recommend a method to use. What would be your intended use for the digitized parts?