Reticle for an object measurement system

摘要

A reticle for an object measurement system comprises a pattern 10 having a plurality of pairs of contrasting elements in the form of black (11', 11'' . . . 14'14'') and white (21 . . . 24) wedges. Each black/white wedge pair defines a path towards a pattern origin 19 such that an edge of an object 50 occluding the path causes a change in contrast adjacent an edge point along the path. The pattern has a series of Gray-coded elements 15 associated with each pair of black/white wedges. The Gray-coded elements are indicative of an absolute coordinate of each edge point at which an object edge crosses a path. A series of triangles 16 associated with each pair of black/white wedges, whose absolute coordinates are known, allow a measurement system to provide accurate coordinates for each edge point.