Abstract:
A presumptive mode computer aided design and drafting system for interactively manipulating and displaying graphic objects that employ predefined rules to govern the geometric layout and logical relationships representing a physical design, schematic or process flow diagram. The system is configured to comply with the rules employed by various design disciplines. Specific interactive computer graphics behavior is dynamically accessed to interactively update graphic object relationships according to rules of geometric conduct. The rules of geometric conduct may be stored in external databases along with parameters to verify the logical relationships of the graphic objects used in the drawing. Object orientation is employed in the software design of the system to allow new devcies or procedures to adopt the behavior of existing definitions. In the preferred embodiment, a selected object floats with a cursor in a graphic environment until located in proximity with underlying graphic objects. The selected object then aligns, jumps and clings to the underlying graphic object or objects according to predetermined rules. For example, the object is automatically rotated, orientated and positioned relative to a cling point into a correct relationship with the underlying object without further input by the operator. Further, the selected object slides along the underlying graphic object maintaining the correct geometric relationship while the operator moves the cursor in proximity with the underlying graphic. The operator either accepts the presumed relationship or moves the cursor away to uncling the selected object.

Description:
FIELD OF THE INVENTION 
     The present invention relates to computer aided design and drafting systems, and more particularly to interactively manipulating and displaying presumptive relationships between graphic objects. 
     DESCRIPTION OF THE RELATED ART 
     At the present time, the layout of drafted documents is based upon predefined geometric constraints for the graphic representation of engineering designs, utility systems, chemical processes, etc. Traditional computer aided methods for producing these types of digital drawings require the computer operator to indicate where and how a graphic object is to be drawn by the computer. The operator indicates an origin, orientation and connection point for the graphical objects and the computer subsequently produces the digital representation suggested by operator input. If the resulting representation is not correct, the operator either deletes the incorrect graphics from the drawing file or manually adjusts the graphics and attempts to create a new representation that meets defined criteria. 
     It is presently known that an operator may press a button on a mouse to provide a “tentative point” to the computer to suggest where an object might be placed. The computer responds by placing a graphic “crosshair” at a precise location nearby the point suggested by the operator. If the point suggested by the operator is close to a key coordinate value from an underlying object in the digital file representing the design, the computer places the tentative point at that location and redisplays the graphic object in a specified color. If the resulting location is desired by the operator, a key is depressed on an input device to accept the tentative point and the specific coordinate values are used one time in the immediately following data input operation. If the coordinate location and associated graphic object determined by the computer is not desired by the operator, the mouse button is pressed again to request another tentative point. 
     Such tentative point mode of operation requires multiple point and click inputs by the operator resulting in rather tedious interaction with a computer aided design and drafting (CAD) system. The locations and geometric selections generated by a CAD system of prior art are often incorrect and must otherwise be adjusted. Further, the operator must be aware of the geometric rules and relationships and usually must be a sophisticated operator or even an expert. 
     SUMMARY OF THE INVENTION 
     A method and apparatus according to the present invention replaces the tentative point mode of computer graphics input with a “presumptive point” mode tied to the motion of the input device. In the presumptive mode of operation, a computer system constantly presumes points of interest, referred to as cling points, which are in proximity with an on-screen pointing symbol or cursor for the operator to accept or reject. Predefined rules are maintained to limit selection to objects of interest and to perform the geometric computations that provide other related functions such as tangent, offset, parallel, alignment, end point, major vector, divided segment, extended segment, intersection and other specific coordinate locations derived from the graphic objects that comprise a digital design. 
     In addition, an interface is provided to accommodate external rule-based input verification procedures, and the newly input graphic object may inherit specific characteristics of underlying object previously accepted. A system according to the present invention eliminates much of the interactive selection and confirmation of graphics components used in drafting of designs, as well as to provide more accurate results in a design. 
     The present invention automatically employs a rule-based database to verify the juxtaposition of graphic objects within the intended context of the design. The interactive behavior of the graphics objects is constrained by a set of geometric specifications that are constructed in advance of digital data input operations. External procedures for the verification of graphic object relationships occur during digital data input operations to avert the creation of invalid representations of designs. Geometric relationships such as parallel, orthogonal, tangent, etc. are automatically provided for performing the accurate layout of design drawings in a dynamic manner. 
     For example, a selected object floats with the cursor and then jumps and clings to an underlying graphic object when the cursor is moved to within a predefined minimum distance called the location tolerance of the underlying object. The selected object clings at a predefined offset, orientation, rotation, etc. relative to the cling point, which slides along the underlying object as the cursor is moved by an operator. Other operations may be performed automatically either interactively or when the selected object is accepted, such as cutting or deleting portions of the underlying objects. These presumptive relationships are automatically made and dynamically updated as the operator moves the cursor and floating object to a desired location. The operator then merely accepts or rejects the presumptive relationship with not further input. 
     A system according to the present invention also offers methods of creating geometric specifications to constrain drafting input operations and produce aesthetically pleasing and geometrically correct results. Techniques are provided for a design analyst to specify the behavior of a graphic object when it is combined with other graphic objects in a design drawing. 
     A system according to the present inventoin preferably includes access to external databases for the provision or extraction of information that is related to the design, system or model. In addition, a base of knowledge is provided which may be accessed to ascertain whether the relationships among new graphic objects being added to the file by drafting operator input operations are valid. 
     The present invention allows an operator to more rapidly produce accurate digital computer drawings that conform to predefined specifications for appearance, content and relationships among the graphic objects that convey cognition for the intent of designs. The computer operator is relieved of the duty of learning the correct layout of graphic objects to assemble a valid representation of a design, system or model. In effect, a system according to the present invention is an “expert” CAD system, so that the operator need not be very knowledgeable to produce correct graphic results and representations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention can be obtained when the following detailed description of the preferred embodiment is considered in conjunction with the following drawings, in which: 
         FIG. 1  is a flowchart diagram illustrating operation of a system according to the present invention; 
         FIG. 2  is a representative computer screen that an operator interacts with using a pointing device to create digital drawings according to the present invention; 
         FIG. 3A  is a graphic diagram illustrating operations performed by a system according to the present invention; 
         FIG. 3B  illustrates an initial cling characteristic of a floating object with an existing, underlying object; 
         FIG. 3C  illustrates a continuing clinging characteristic according to the present invention; 
         FIGS. 3D-3F  illustrate possible behaviors that can be applied to a floating object while it is clinging to an underlying object; 
         FIGS. 4A-4D  illustrate yet further examples of the cling characteristic using a system according to the present invention; 
         FIG. 5  illustrates how TEXT is handled in context with other graphic objects; 
         FIGS. 6A-6D ,  7 A- 7 D,  8 A- 8 E and  9 A- 9 E illustrate various examples of objects including alignment vectors for aligning the graphic objects and modifying underlying objects; 
         FIGS. 10A and 10B  illustrate alignment of two pipe objects using alignment vectors; 
         FIG. 11  illustrates the present invention used to implement closed clip region objects for partial deletion of graphic objects in a design; and 
         FIG. 12  is a diagram of a computer system implemented according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 12  illustrates a computer system  1200  implemented according to the present invention. The computer system  1200  is preferably an IBM XT, AT or IBM compatible computer system or any comparable computer system capable of operating as a computer aided design and drafting (CAD) system. The computer system  1200  includes a display device or monitor  1202  for viewing a graphic environment. A keyboard  1204  is also provided for inputting text, as well as a pointing device  1206 , such as a mouse or the like, for manipulating graphic objects on the screen of the monitor  1202 . A main system unit  1208  includes the necessary logic for running software and processing commands as known to those skilled in the art. For example, a processor  1210 , such as an  80386 , i 486 , Pentium, etc. is coupled to memory  1212  for executing software according to the present invention. 
     The computer system  1200  is preferably implemented as a CAD system according to the present invention by loading software into the memory  1212  for execution by the processor  1208  for receiving input and commands from the keyboard  1204  and mouse  1206  and generating a graphic output on the display  1202 . Graphic parameters and geometric relationships are defined in database files stored in memory. It is noted that alternative computer systems and interfaces are contemplated, such as three-dimensional holographic displays for improved visual representation of the graphic environment. 
     Referring now to  FIG. 1 , a flowchart diagram is shown illustrating operation of a system according to the present invention. The flowchart illustrates that the system is designed to create representations that conform to predefined specifications for the geometric and logical relationships that exist among graphic objects in a computer based drawing representing a design, system or model. 
     In step  100 , the applicable specific geometric relationships such as alignment, offset, etc. are defined for each entity that is represented in one or more drawings. Additionally, any relationships that are based upon associated database attributes are tabulated and encoded. In the next step  102 , the graphic objects used as geometric constraint components are created according to specifications for the desired functional behavior. In the next step  104 , any additional generic geometric constraints that may apply are determined and tabulated. 
     In the next step  106 , the constraint definitions for the object are created as a collection of digital data that appears in a recognizable form such as a graphic symbol. The symbol comprises a series of components, some of which are always displayed on a computer screen as the normal graphic representation of the associated object, some components which are not normally displayed on the screen except as an aid to their definition, some logical verification components are tabulated as a digitally encoded rule-based record that is associated with the symbol, and some components are stored as textural specification data that is provided to the control software at the moment the object is activated for inclusion in the design, system or model. The textual data may be any one of several formats, such as ASCII (American Standard Code for Information Interchange) or the like. 
     In the next step  108 , an object is selected for input by the operator using any of several techniques including the selection of a graphic icon from a computer screen ( FIG. 2 ) that represents the object, typing in a keyed command that causes the object to become active, or any other means of indicating to a software program that the desired object is to be added to the drawing using the geometry processing engine. 
     In the next step  110 , the object is read into the geometry processing engine and graphically interacts with other objects according to the specifications provided in the symbolic definition and the constraints of any external database attribute or knowledge based verification process. Feedback is provided to the operator to indicate the integrity of the proposed relationships between the new object and existing graphic objects in the digital drawing. Such feedback includes changing the color of the affected graphic objects, providing additional on-screen motions to the affected symbol to indicate a correct or incorrect validation result, or providing unique auditory sounds to indicate a correct or incorrect validation result. In the next step  111 , the graphic representations are verified against a rule-based database. 
     In the next step  112 , the object is accepted by the operator as being a correct representation at which point the geometry engine inserts the symbol in context into the graphic representation of the design, system or model, taking into account all geometric control specifications provided with the symbolic definition. Once the new graphic object is added to the existing digital file, the sequence of operations returns to step  108  and drafting operations continue. In particular, steps  108 - 112  are repeatedly performed in sequential manner until the operator has added all desired objects, and operation is then completed. 
     Referring now to  FIG. 2 , a representative computer screen  200  is shown in the context of interactive computer aided design software. Steps  100 - 106  have previously been performed at this point so that the operator interactively selects objects in step  108  and accepts a selected object in step  112  until the design is completed. The operator selects objects with a cursor as known for window environments, although the present invention is not limited to a windows environment. A tool palette  202  is provided containing one or more icons that indicate the graphic objects that are available for processing by the geometry engine. A series of objects  204  that have been previously placed appear on the screen  200 , which in this particular case is a series of pipes for a plumbing system. Of course, other types of objects are contemplated, such as engineering designs, electrical schematics, utility systems such as power generation and distribution grids, chemical processes, etc. The objects  204  thus are represented in the underlying design file. An optional control panel  206  is provided to specify any additional geometric function that are to apply to the symbolic object. The balance of the screen depicts a typical interactive computer aided design environment. 
       FIG. 3A  is a graphic diagram illustrating operations performed by a system according to the present invention. A computer screen  300  similar to screen  200  is shown including a tool palette  302  for selecting graphic objects. The operator selects a symbol from the tool palette  302  and activates an object  304  with the cursor  306 , where the geometry processing engine performs the activation as described above. The selected object  304  floats with the cursor  306  (thus called a floating object) at a particular displacement, rotation and orientation according to predetermined criterion. In the example shown, the floating object  304  maintains zero degree rotation with its origin on the cursor  306 . 
     Once selected, the operator moves a pointing device to move the cursor  306  and the object  304  within the computer screen  300  along any desired path  308 , and eventually within proximity of an underlying object  310 . The floating object  304  is selected and shown on the computer screen  300  but is not made part of the underlying design file until accepted at a desired location by the operator. The underlying object  310  has already been previously accepted and therefore part of the underlying design file. Throughout this disclosure, an underlying object exists in the underlying design file, but a selected object to be placed is not made part of the design file until accepted by the operator. 
     A predetermined and programmed location tolerance, illustrated with a dotted circle  312  but normally not displayed, identifies a minimum perpendicular distance which determines when the object  304  is close enough to the underlying object  310  to establish an association or graphic relationship. When the designated origin point of the object  304  moves to within the location tolerance  312  with respect to the underlying object  310  or with respect to any other object where a graphic relationship is allowed, the “cling” mode of interaction is invoked whereby the floating object  304  “jumps” onto the underlying graphics object  310  as though it were magnetically attracted. In  FIG. 3A , the origin and cursor  306  are positioned at a distance from the underlying object  310  greater than the location tolerance  312 , so the object  304  remains floating with or otherwise attached to the cursor  306 . 
       FIG. 3B  illustrates the initial cling characteristic of a floating object with an existing, underlying object. In particular, once the object  304  is within the location tolerance of the underlying object  310 , the floating object  304  jumps from the cursor  306  to cling to the underlying object  310 . In the example shown in  FIG. 3B , the jump is the shortest or perpendicular distance where the origin of the object  304  aligns and is coincident with the closest or cling point  313  of the underlying object  310 . The cling point  313  is typically displayed on the screen  300  for purposes of visual feedback to the operator, although it may alternatively be transparent or invisible if desired. 
       FIG. 3C  illustrates how the floating object  304  magnetically clings to the underlying object  310  as the cursor  306  is moved in proximity with the underlying object  310 . As the pointing device is moved by the operator, the object  304  follows the extend of the underlying object  310  and, if an offset distance, rotation angle, or other geometric specification has been defined, the object  304  assumes a position with respect to the geometric specifications and the active “magnetic” cling point  313  on the underlying object  310 . In the example shown in  FIG. 3C , a programmed rejection tolerance, illustrated as a dotted circle  314  about the origin of the object  304 , is defined where the object  304  remains clinging to the underlying object  310  while the cursor  306  is within the rejection tolerance. The rejection tolerance is preferably larger than the location tolerance to achieve a hysteresis effect. It is noted that the location and rejection tolerances are different parameters which are toggled so that only one is active at a time. The location tolerance determines when an object clings to an underlying object and the rejection tolerance determines when a clinging object unclings from the underlying object. 
     The cursor path  308  and the underlying object  310  are extended to illustrate the cling characteristic. The floating object  304  “slides” in alignment with the underlying object  310  as the cursor  306  traverses the path  308 . In particular, when the cursor  306  is at the locations  320 ,  322 ,  324  and  326  as shown, the floating object  310  assumes the corresponding positions  330 ,  332 ,  334  and  336 , respectively. It is noted that the cursor  306  remains within the rejection tolerance defined for the floating object  304  for the positions  330 ,  332 ,  334  and  336 . 
     If the operator desires to “uncling” from the underlying graphic object  310 , operator moves the cursor  306  a distance greater than the rejection tolerance away from the underlying object  310  and the floating object  304  “jumps” away from the underlying object  310  to the cursor  306  as though it were magnetically repelled. This is shown at a location  328  of the cursor  306 , where the floating object once again floats with the cursor  306  as shown at the position  328 . If there is an additional specification for the logical relationship between the floating object  304  and the underlying object  310 , and if that relationship is not valid for the particular case, the floating object  304  does not “cling” to and is prevented from floating near the underlying object by an algorithm that displaces the floating object&#39;s position with respect to the on-screen pointing device. An additional warning such as an auditory “beep” or visual cue such as a sudden red color change in the floating object  304  is issued by the computer. 
       FIGS. 3D-3F  illustrate possible behaviors that can be applied to the floating object  304  while it is clinging to an underling object  310 . These behaviors are predefined according to geometric constraints for a given object.  FIG. 3D  illustrates that the object  304  may be spun about an initial cling point  313  by manipulating the cursor  306  around the cling point  313 , in contrast with  FIG. 3C  showing the object  304  predefined to maintain a zero degree orientation regardless of its location. Further, the object  304  does not slide but sticks to the initial cling point and rotates according to movements of the cursor  306 .  FIG. 3E  shows the object  304  positioned at a specified perpendicular offset  315  from cling point  313  in the direction of the cursor  306  and maintaining a zero degree orientation. Note that the floating object  304  jumps to the opposite side of the underlying object  310 , as shown as  304 A, when the cursor  306  traverses from one side to the other of the underlying object  310 .  FIG. 3F  shows the object  304  ( 304 A) at a 180 degree rotation of the underlying object  310  at a specified perpendicular offset  315  from cling point  313  in the direction of the cursor  306 , again on opposite sides of the underlying object  310 . Other variations are possible, of course, including multiple instances of the floating object, such as a mirror image of the floating object at a specified perpendicular offset from “cling” point in the direction of the cursor  306 , etc. 
       FIGS. 4A-4D  illustrate yet further examples of the cling characteristic using a system according to the present invention. In each case, a cursor  406  with a floating object  404  is moved within a screen  400  along a path  408  relative to an underlying object  410  already placed on the screen  400 . The object  404  is kept a predefined distance from the underlying object  410  relative to a sliding cling point, which slides along the underlying object  410  following the cursor  406 . The floating object  404  flops to the other side of the underlying object  410 , as indicated at  404 A, when the cursor  406  crosses over the underlying object  410  in a similar manner as described previously. It is noted that only one object is shown at any given time in the example of  FIGS. 4A-4D , where the designations  404  and  404 A illustrate orientation of the same object on opposite sides of the underlying graphic object  410 . 
     Other graphic relationships define the orientation and rotation of the floating object  404  based on the position of the cursor  406 . In  FIG. 4A , the object  404  is mirrored about the underlying object  410  when flopped to  404 A. In  FIG. 4B , the object  404  is mirrored about a perpendicular  415  when flopped to  404 A. In  FIG. 4C , the object  404  is mirrored with respect to both the perpendicular  415  and the underlying object  410  to  404 A. In  FIG. 4D , the object  404  maintains a parallel relationship to  404 A. 
       FIG. 5  illustrates how TEXT is handled in context with other graphic objects. Once the related symbolic object  510  has been drawn on a screen  500 , a TEXT annotation “floats” with a cursor  506  while obeying constraints for placement of the TEXT. The TEXT is made to align to the underlying graphic object  510  using specified offsets, parallels and tangencies. In the example shown, the TEXT begins with an initial location tolerance, identified by dashed circle  512  and a larger rejection tolerance as illustrated by a dashed circle  514 , both with respect to an origin of the TEXT. At first, the TEXT floats with the cursor  506  until the cursor  506  is within the location tolerance, at which time the TEXT jumps to align parallel and at a perpendicular tangent with respect to the underlying graphic object  510 , but separated by a predefined offset  515 . While the cursor  506  is moved along a path  508 , within the rejection tolerance, the TEXT aligns tangentially with the underlying object  510  at the defined offset  515 . This is illustrated at cursor positions  520 ,  522 ,  524  and  526 . When the cursor  506  crosses over the underlying object  510  at point  530 , the TEXT preferably jumps to the opposite side, but maintains an orientation to allow the TEXT to be read in normal upwards fashion. A dotted line  532  illustrates the path that the TEXT follows. Furthermore, a characteristic is defined where the TEXT automatically re-aligns itself at 180 degree increments, which occurs between positions  524  and  526 , to maintain upward reading orientation. When the cursor  506  is moved outside the rejection tolerance, the TEXT jumps back to float with the cursor  506  at an origin, and the location tolerance is re-established. 
       FIGS. 6A-6D ,  7 A- 7 D,  8 A- 8 D and  9 A- 9 D illustrate various examples of alignment vectors for inserting and cutting graphic objects.  FIG. 6A  illustrates an object  604  with a single alignment vector  605  having two points, an origin point  605 a for geometry calculations and an alignment point  605 b for establishing orientation and direction of the alignment vector  605  and the object  604 . Although the object  604  is shown as a simple rectangle, it can be any object following particular alignment rules, such as pipes, electrical components, etc. 
       FIG. 6B  shows a screen  600  with an underlying object  610  and a floating object  604  floating with a cursor  606  for insertion, where the underlying object  610  is illustrated as a single line segment. The object  604  includes an alignment vector  605  where the cursor  606  preferably aligns with the origin point  605 a. A location tolerance is predefined and indicated by a circular outline  612  around the cursor  606 . The object  604  is moved with the cursor  606  along a path  608  and brought within the location tolerance of the underlying object  610 , where the object  604  snaps to and aligns with the underlying object  610 , as shown in FIG.  6 C. In particular, the origin point  605 a jumps to a cling point  613  and the object  604  and alignment vector  605  rotate to align so that the second point  605 b lies on top of the underlying object  610 . The object  604  now clings and slides along the underlying object  610  in a similar manner described previously, where a rejection tolerance is usually defined for maintaining cling with movement of the cursor  606 . 
     It is noted that the eventual desired result is to “connect” the object  604  to the underlying object  610  at the origin point  605 a, thereby affecting the underlying object  610  in the data base as well as graphically, if desired. In the example shown in  FIG. 6C , the underlying object  610  is preferably split into two separate line segments  610 a,  610 b at the origin point  605 a of the alignment vector  605 . The underlying object  610  is preferably immediately modified during the cling action and dynamically updated as the object  604  is moved along the underlying object  610 , where the respective lengths of the line segments  610 a,  610 b are modified accordingly. Alternatively, the underlying object  610  is not affected until the object  604  is actually accepted at a desired location. 
     In  FIG. 6D , the operator has accepted an appropriate location of the object  604 , where the underlying object  610  is split into two separate vectors  610 a and  610 b at the common origin point  605 a. It is appreciated that the operator had to only select the object  604 , move the cursor to within a predetermined proximity of an underlying object  610 , and the system automatically aligned the object  604  with respect to the underlying object  610  and further modified the underlying object  610  according to predefined rules. Then the operator simply moves the cursor in proximity of the underlying object  610  to select the desired location, and accept the object  604  and the object  604  is added. 
       FIG. 7A  illustrates an object  704  including a double alignment vector  705  in collinear mode with two spaced vectors  705 a and  705 b, each including origin points and alignment points for directional purposes in a similar manner as shown in FIG.  6 A. The separation between the respective origin points of the alignment vectors  705 a and  705 b defines a cut length for cutting an underlying object. In  FIG. 7B , a screen  700  is shown including an object  704  selected for connection to an underlying graphic object  710 , which is another line segment as shown. When the object  704  is moved into proximity with the underlying object  710  as shown in  FIG. 7C , the origin point of vector  705 a clings to a cling point  713 , the object  704  and vectors  705 a,  705 b rotate to align with the underlying object  710 , and the underlying object  710  is divided into two separate line segments  710 a,  710 b separated by the predefined cut length. Again, the underlying object  710  is either modified or cut immediately or modified after the object  704  is actually accepted. Again, the floating object  704  clings and slides along the underlying object  710  while the cursor  706  is moved within the predefined proximity or rejection tolerance, continually redefining the location of the cut. 
     Eventually the operator selects the location of the object  704 , and the object  704  is inserted and the underlying object  710  is appropriately divided as shown in FIG.  7 D. As a practical example, if a floating object includes specific definitions of collinear vectors, the geometry engine cuts the underlying linear graphic object and connects the resulting linear segments to the collinear vectors. This has the effect of breaking a line and inserting a device that forms part of the line, such as a fuse on a circuit schematic. 
       FIG. 8A  illustrates an object  804  including double alignment vectors  805 a,  805 b in collinear mode with an additional orthogonal alignment vector  805 c. The collinear vectors  805 a,  805 b are two spaced vectors, where all three vectors include an origin point and an alignment point for directional purposes as described previously. The orthogonal alignment vector  805 c is preferably placed between and orthogonally aligned with the collinear vectors  805 a,  805 b as shown. The separation between the collinear vectors  805 a,  805 b defines a cut length. 
     In  FIG. 8B , the object  804  with the alignment vectors  805 a,  805 b and  805 c is selected for interaction with underlying graphic objects  810  and  811 , where the primary vector  810  orthogonally intersects a secondary vector  811  at a point  820  as shown. Again, a screen  800  is shown including a cursor  806  for locating the object  804 . 
     When the object  804  is in proximity of the underling object  810  as shown in  FIG. 8C , the collinear vectors  805 a,  805 b cling, align and cut the underlying primary vector  810  into two separate vector objects  810 a,  810 b separated by the predefined cut length in a similar manner as described previously. The origin point of the vector  805 a has a location tolerance for jumping and clinging with the primary vector  810 . The object  804  clings and slides along the primary vector  810 . 
     As illustrated in  FIG. 8D , the orthogonal alignment vector  805 c also has a separate location tolerance defined for its origin for clinging to the secondary vector  811 . Thus, when the origin point of the orthogonal alignment vector  805 c is within its location tolerance with the secondary vector  811 , the object  804  and alignment vectors  805 a,  805 b and  805 c jump so that the origin and alignment points of the vector  805 c align with the underlying vector  811 . The operator may move the cursor  806  about a rejection tolerance, where the object  804  remains static and aligned with the intersection point  820 . 
     In  FIG. 8E , the operator accepts the result, and the underlying primary segment  810  is divided into two collinear line segments  810 a,  810 b separated by the cut length, where the cut length is divided on either side of the secondary vector  811 . In the example shown, the primary vector  810  is divided equally on either side of the secondary vector  811 , although unequal divisions and non-orthogonal intersections, e.g. isometric, etc. are just as easily achieved as desired. 
       FIGS. 9A-9E  are similar to  FIGS. 8A-8E , except illustrating primary  905 a,  905 b and secondary  905 c,  905 d collinear alignment vectors defining two separate cut lengths for the primary  910  and secondary  911  underlying objects, respectively. The primary and secondary vectors  910 ,  911  are divided into two portions  910 a,  910 b and  911 a,  911 b, respectively, divided by respective cut lengths, and the object  904  is aligned and places as desired. 
       FIGS. 10A and 10B  illustrate operation of alignment vectors for aligning an underlying T pipe object  1010  and a selected elbow pipe object  1004  using alignment vectors on a screen  1000 . The underlying T pipe object  1004  includes an alignment vector  1005  and the T pipe object  1010  includes an alignment vector  1017 , each with an origin point and an alignment point. The operator selects the elbow object  1004  having a predefined location tolerance about the origin point of the vector  1005 . The elbow object  1004  floats with the cursor  1006  it is within the location tolerance of the origin point of the alignment vector  1017  of the T pipe object  1010 , where the elbow object  1004  is automatically rotated and positioned so that the respective origin points and alignment points of each of the alignment vectors  1005 ,  1017  overlap. In this manner, the two objects  1004  and  1010  are automatically aligned with each other by the system, and the operator need only accept or reject the proposed relationship. In particular, if the operator intended to connect the objects  1004 ,  1010  as proposed, the relationship is accepted, and if not, the operator simply moves the elbow object  1004  beyond the rejection tolerance for connection with another object as desired. 
     It is noted that the particular alignment vectors described herein are for purposes of illustration. Thus, alignment vectors need not be collinear nor orthogonal but may be aligned at any desired orientation and angle. 
       FIG. 11  illustrates the present invention used to implement objects including clip regions for partial deletion of underlying graphic objects in a design. A palette  1102  is provided on a screen  1100 , where the palette includes three objects  1104 ,  1106  and  1108 , each having corresponding clip patterns  1104 a,  1106 a, and  1108 a, respectively. Also provided on the screen  1100  is a set of underlying object symbol patterns, including a pattern of splines  1110 , a horizontal line pattern  1112  and a vertical line pattern  1114  intersecting one another as shown. The operator selects one of the objects  1104 ,  1106  and  1108  from the palette  1102 , and the selected object floats with the cursor as the cursor is moved across the screen  1100  by the operator. As the selected object coincides with or covers the patterns  1110 ,  1112 , or  1114 , a portion of all or certain ones of the underlying patterns  1110 ,  1112  and  1114  that are coincident with the corresponding clip region of the selected object is deleted. 
     In particular, the clip pattern  1104 a deletes the coincident portion of the pattern of splines  1110 , but otherwise does not affect the horizontal or vertical pattern of lines  1112 ,  1114 . The clip pattern  1106 a deletes the coincident portion of all of the patterns  1110 ,  1112  and  1114 . The clip pattern  1108 a deletes the coincident portion of the horizontal and vertical line patterns  1112 ,  1114 , but does not affect the underlying pattern of splines  1110 . This partial deletion is contrasted with simple masking capability, where the graphic portion of the object is obscured but the object “remains” in the graphic file. Although the present invention may be used for partial masking, partial deletion involves actually deleting the coincident portion of the underlying graphic objects in a selective mode. 
     It is noted that the partial deletion may be performed interactively as the selected and floating object is moved across the screen  1100 . However, this is computationally intensive and may cause a computer system to slow down considerably. Thus, the object is usually drawn and the underlying deletions are preferably performed upon acceptance of object at a desired location. 
     An example of objects including the clip patterns to partially delete any underlying graphic object elements is TEXT, where it is desired to create “white space” for TEXT annotation. The objects to be deleted are contained in a specification for that type of annotation. In  FIG. 5 , for example, if the TEXT overlaps certain underlying objects, a portion of the object coincident with the TEXT is deleted. Also, if the definition of the floating object includes a closed shape drawn with specific graphic parameters, the geometry object engine causes the CAD system to partially delete all specified graphic objects that fall within the defined region. This has the effect of “cleaning up” graphic elements that would otherwise appear to be visually merged with the floating object. 
     It is now appreciated that a presumptive mode CAD system according to the present invention interactively manipulates and displays selected objects according to predefined geometric relationships for acceptance by an operator. The system automatically exhibits the correct graphic and geometric relationships in an interactive fashion. Thus, the present invention allows an operator to more rapidly produce accurate digital computer drawings that conform to predefined specifications for appearance, content and relationships among the graphic objects that convey cognition for the intent of designs. The computer operator is relieved of the duty of learning the correct layout of graphic objects to assemble a valid representation of a design, system or model. In effect, a system according to the present invention is an “expert” CAD system, so that the operator need not be very knowledgeable to produce correct graphic results and representations. 
     Although the system and method of the present invention has been described in connection with the preferred embodiment, it is not intended to be limited to the specific form set forth herein, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents, as can be reasonably included within the spirit and scope of the invention as defined by the appended claims.