If you want to measure the shape of a metal surface, you can gently touch it with a bunch of sharp springs, insulated from one another and constantly separately tested for electrical continuity with the metal. By moving this springy brush around, you can measure when each wire enters and leaves contact with the surface; by only barely touching the surface, you keep the stresses on the spring tips low enough to avoid plastic deformation. Using springs with a slight curve or coil to them, rather than straight bristles, reduces the stress for a given strain, protecting the tips from being blunted.
It’s important that the bristles not bend plastically or creep, so it is advisable to make them out of a brittle substance with a high melting point, such as tungsten, or such as aluminum oxide with thin metal plating. Sharp points can be achieved by growing crystals with a naturally acicular habit, like mullite or some phosphates of calcium, which will normally have atomically-sharp points which will be blunted slightly by the metallic plating, or by electrolytic sharpening of metallic points.