Abstract: A computer aided drafting (CAD) procedure presents, for a three dimensional (3D) object to be modeled in a general purpose computer, dimensional and tolerance parameters appropriate to changes of view or parameters. The procedure requires but one model, the three dimensional solid model, for producing both dimensioned displays of the model and dimensioned drawings of views of the model. Dogleg extension lines are used to express 3D dimensions without ambiguity. These dogleg extension lines facilitate the presentation of information on paper or on a display screen and permit convenient alteration of presentations of 3D illustrations, with automatic correction of dimension and tolerance presentation. The operator of the CAD system enters dimension and tolerance information on a plan or elevation view, and this information is automatically converted to an appropriately corrected and presented axonometric presentation.

Abstract: A method and apparatus for determining the X--Y coordinates on the raster of the intersection of two curves one of which is stored in the display system raster refresh buffer. The second curve is generated by a curve generator or some other source of sequential X--Y coordinate data defining the X--Y coordinates on the raster where the second curve would lie. As each X--Y coordinate is generated by curve generator it is translated into a buffer address and the contents of that address in the buffer memory are accessed and a determination is made to see if said first curve exists at that address. If an element of the first curve is found to exist in the buffer store at the generated address location, it is known an intersection point has been found and the appropriate X--Y address is gated from the system to utilization means.