A graphic display apparatus for generating a vector comprises registers for storing a value R of a vector discrimination, a positive increment P and a negative increment N, and flip-flops for storing magnitude information of .DELTA.X, .DELTA.Y, and .DELTA.X and .DELTA.Y. An address counter of a refresh memory is counted up or down in accordance with the contents of those flip-flops. A control circuit for updating the value R of the vector discrimination is also provided, so that the vector can be generated at a high speed. The registers and the flip-flops are constructed in two stages so that data for generating the next vector can be prepared while the current vector is generated.

In raster data plotting of graphic information, vector data comprising the plot is generated by the host computer via the user's application program. For maximum plotter efficiency and relief of host system time, vector to raster conversion is carried out by an offloading processor which receives vector data ordered in vector bands constituting the plot. Vector data in each band is received in random order and is initialized for vector computational values. The computational values for each vector are stored in parallel format in a vector memory in the initialized random order for subsequent retrieval in parallel format for vector to raster processing of each scan line of the band and then restored in parallel format in the vector memory if the vector is still active. A vector type, designating vector orientation relative to Cartesian coordinates, is one of the computational values for each vector. The time required for vector to raster conversion is further enhanced by processing each vector directly according to its vector type found in the microcode of the processor.

A curve follower or line tracing system for converting the common representation of patterns of lines into features which are readily usable as inputs to an adaptive information processing system such as a Nestor adaptive module. The problem addressed by this system is how to sequentially identify, from a global exposure or tracing of a curve, the starting and subsequent points of the curve in the same manner as tracing it by hand. In the curve follower, an array of light sensitive elements located on a grid identify a line at the grid points. Since the end point of the line has a single neighbor, it is readily located. The identification of an end point is used to subsequently inhibit further identification of the end point and create another point which is similar identified. Overall biases may be employed to define a preferred line direction. Once the resulting sequence is obtained, the line may be coded.