To duplicate an object it is sometimes necessary to accurately measure it.  There are basically two directions to go: To measure point by point with a digital probe or other point measuring device or to use an optical scanner to obtain the desired information.

The digital probe requires a CNC system that is used to obtain point by point data measurements.  When the highest accuracy is needed that is the way to go.  Commercial probes are very expensive, many thousands of dollars.  Here is a link to how to make your own and the software to convert the measured data.
www.vinland.com/Touch-Probe.html