1. In a robotic welding operation wherein welding current conducted by the nonconsumable electrode of a welding torch generates an electric arc whose heat forms a molten weld puddle in the workpiece, and a vision system integrated with said torch provides images of said weld puddle to control the welding process, the improved method of measuring puddle geometry parameters comprising: sampling image intensities along N radial rays intersecting only the trailing edge of said weld puddle, using the torch electrode as the origin; determining pudlde boundary point data by processing each radial image intensity waveform to identify patterns that indicate potential edge points; prefiltering the puddle boundary data to remove extraneous points; estimating in real time by means of a least-squares algorithm the area and maximum width of the elliptical weld puddle; and passing these values to a closed-loop weld process control system.