Manual 2D contoure scanner idea

Hello...

I need to fit wooden board to fit shape of object. The object can be around 3m in diameter. Making template is just to tedious. So I just wonder if I can use pantograph https://en.wikipedia.org/wiki/Pantograph like machine to make job easy. If I fit encoder where arm is bolted to object and another encoder to "elbow" I think I can trace shape manually and use data to make program CNC machine to cut that. Does someone use something cheap and easy to do similar task? All cheap 3D scanners I tested was complete failure. The precision is to coarse. I want at least 1mm precision. As board is 2D object the 3D scan is overkill too. Any ideas?