Patent GB-1513978-A (GB)
Title: Data processing system
IPC: G06T11/20
Filed: 1976-08-17
Abstract: 1513978 Processing graphic data INTERNATIONAL BUSINESS MACHINES CORP 17 Aug 1976 [22 Sept 1975] 34145/76 Heading G4A Graphic data entered in the form of coordinates representing points on a rough sketch 12 (Fig. 1) to generate a first list is processed to produce a second list in which points such as B and C (Fig. 2) are given the same vertical component B v , C v  by linking the location associated with the coordinate C v  by a pointer to the location storing the coordinate B v , the second list being used to provide the output sketch 30. Derivation of first list (Fig. 7). As described a first pointing sequence list PSL1 is derived by touching with stylus 34 (Fig. 1) two registration points (37, 38, Fig. 4, not shown) of an overlay keyboard (36) to determine the position of its keys, then touching one of the function keys e.g. OBJECT to generate a line function header of the first entry in the list. The points A-E (Fig. 2) at the corners of the drawing to be constructed are then sequentially touched. This results in the horizontal and vertical components (A H , A V  etc) of the points being stored as first and second document entries in the list. Next the dimension key is operated and the points are again touched with the stylus, a position F (Fig. 2) at which a dimension is to be recorded on the finished drawing and a further point, e.g. G to indicate the direction of the record (i.e. horizontal) to get a direction of control word being also touched. The dimension, e.g. 4À0 is then entered. This process is repeated until all the dimensions have been entered. Each entry comprises two bytes, the first byte having control information to indicate the type of entry, e.g. header, document entry, non axial line indicator (to indicate whether a line follows the axis) and a join indicator (to indicate for example that point E is to be aligned with point A) and a second information byte. In the case of a document entry half the first byte and all the second byte i.e. bits 4-15 represent the coordinate value. Derivation of second list (flow drawings of Figs. 13A, 13B). When the operator touches the rectify key with the stylus, a second pointing sequence list PSL2 is formed from the first list which includes pointers to earlier identical information in the list. A routine CONL (flow drawings of Figs. 14A, 14B, not shown) is called up for each point A-E on the drawing, this routine including a pointer routine L (flow drawing of Fig. 15, not shown). This results in for example the entry C V  of location 7 of Fig. 7 storing the vertical component of the point C being replaced by an entry in which bit 2 is set to a "1" to indicate a pointer and the location entry number 5 (that is the location of entry B V  which has the same vertical component) is entered in bits 4-15. Multiple pointers may occur, e.g. E V  to D C  to A V . Pointers are also included in the document reference entries relating to dimensions to link for example location 13 to location 4. This ensures that when a value is altered, e.g. B H  it need only be altered in one location since this location is pointed to by all other locations requiring this information. The pointers are inserted by each horizontal/vertical component in the list being examined to determine whether the line to it from the previous point is vertical/ horizontal. Alignment is effected with the axes with which the two points being considered on the original rough sketch 12 make an angle of less than 45 i.e. if A H -B H  .. A V -B V  then the line AB is aligned with the horizontal axis and the vertical component of B has a pointer to the vertical component of A inserted. Proportioning (flow drawing of Fig. 13C not shown) is effected by the point defined by the first pair of document entries, i.e. A being taken as the origin and the horizontal component A H  of this point being fixed (by setting bit 4 to 1). This results in all entries with pointers to A H  being fixed (i.e. B H ). The dimension in location 20-22 of Fig. 7 is then used to fix C H  by algebraically combining the dimension with the fixed coordinate. After all related horizontal dimensions have been used the vertical coordinate A V  is fixed and the process repeated. The remaining coordinates are then fixed using the horizontal and vertical dimensions from already fixed points. An under dimension test may be performed to check that sufficient dimensions to complete the drawing are provided. Routines are also given for performing proportion functions for circular drawings and for inserting leader lines.