Method and apparatus for processing a freehand sketch

A computerized method of drawing provides sketching-type drawing capabilities in a computer-aided design (CAD) environment. Geometrical drawing parts or elements, sketched through a hand-controlled indicator and lacking in the precision criteria or standards associated with formal drawings, are recognized and interpreted as points, straight lines, open arcs, circles and ellipses. Delete and "areafill" symbols, similarly, are recognized and interpreted. The method also provides the capability to distinguish and interpret relatively complex, multiple-part or element strokes. This is done by determining break locations for the elements along the stroke, and by recognizing these elements before re-constituting a stroke meeting precision criteria. A variety of geometrical constraints which are important in a CAD environment, including coincidence, parallelism, tangency and relimitation, are also recognized and imposed. The recognizing of geometrical elements includes the use of pattern recognition and the use of a neural net. The determination of breaks incorporates the calculation of functions representative of changes in angle, of curvature, and of changes in slope, and the classification of information elements representative of locations, based on such calculations.

FIELD OF THE INVENTION
 The invention pertains to the field of computerized drawing methods, and in
 particular to methods which incorporate the providing of a drawing path
 satisfying precision criteria, from a drawing path lacking such criteria
 which is followed by a drawing indicator.
 BACKGROUND OF THE INVENTION
 The use of computers and computerized methods to provide drawings and
 designs is becoming more and more common.
 A goal of computer-aided design (CAD) is to provide a designer with the
 capability to describe a design, analyze a drawing for a design, modify
 the design, and store copies of the drawings at all phases of the
 development process. Progress in CAD systems and methods, in some sense,
 can be measured by the flexibility offered to the designer and the
 complexity of the design and drawing that is possible.
 The typical CAD approach calls for the user or designer to specify a
 geometric element such as a point, line or circle, and then to specify the
 size features of the element where applicable. By way of example, the user
 or designer might specify a circle, locate the center of the circle by
 positioning a cursor at the center, and then specify the size by moving
 the cursor a distance from the center equal to the desired radius for the
 circle. The system would then execute a drawing for such a circle and
 display it to the user. The information in the system and the display then
 reflects a precise circle (within the limits and tolerances of the
 system). Other precise geometry, then, can be added to the drawing using
 similar or analogous operations.
 This approach, including the interaction with the user, of course is not in
 accordance with the natural way that human beings create drawings. That
 natural way involves the movement of a drawing implement by the user's
 hand. Further, many designers are most creative in "sketching out"
 drawings lacking in the standards applicable to formal drawings for a
 design.
 The device sold by Apple Computer Inc. under the name Newton provides some
 sketching capabilities, perhaps best described as a "notebook" capability
 in a non-CAD environment. It is adapted to create more precise-looking,
 single-element paths, such as circles and ellipses, and more
 precise-looking, multi-element paths, such as a series of straight lines,
 from sketching by a user. It is also adapted to incorporate and impose
 concomitant geometric constraints, such as coincident end points for
 adjacent line elements.
 The present invention provides sketching-type drawing capabilities
 consistent with and incorporated into a CAD environment. This includes a
 variety of geometrical constraints between drawing parts and elements
 which are of significance in a CAD environment. The geometrical drawing
 parts or elements include points, straight lines, open arcs, circles and
 ellipses.
 With the capability to interpret a sketched indicator path as any one of
 these, there is also the capability to distinguish and recognize, delete
 and "areafill" symbols.
 It also provides the capability to distinguish and interpret relatively
 complex multiple-element strokes. It does this by determining break
 locations for the elements along the stroke, and recognizing these
 elements before re-constituting a stroke meeting standards for precision.
 SUMMARY OF THE INVENTION
 In accordance with aspects of the invention directed to drawing part or
 element sketching, recognizing and defining, a computerized method is
 provided for generating information representative of a drawing path
 lacking in certain precision criteria and transforming the information to
 information representative of a drawing path not lacking in such precision
 criteria. A group of indicator information elements representative of
 locations of movement for an indicator in a path lacking in certain
 precision criteria, is generated. A group of transformed information
 elements representative of locations is then generated in response to
 these indicator information elements. The transformed group is operated on
 with a neural net and classified in response to this. Then, in response to
 this classifying, characteristics for the group of indicator information
 elements are generated, and a modified group of information elements
 representative of locations for a modified path not lacking in the
 precision criteria, is defined.
 The modified group of information elements, as one example, can be
 representative of an open arc. The neural net includes output
 classifications representative of a circle, an ellipse, a plurality of
 arcs and a delete symbol.
 The generating of the transformed group of information elements can include
 the transforming of the group of indicator information elements to a group
 of information elements representative of a group of rotated, scaled,
 translated and mapped locations in a predetermined grid. This group of
 information elements, where it is representative of locations in the
 predetermined grid which in turn are representative of a closed path, can
 be further transformed to a group representative of locations in the
 predetermined grid which in turn are representative of a translated closed
 path. Similarly, where the referenced group of information elements is
 representative of locations in the predetermined grid which in turn are
 representative of an arc open in one direction, the group can be further
 transformed to a group representative of locations in the predetermined
 grid which in turn are representative of an arc open in the opposite
 direction.
 Additionally, information associated with the modified group of information
 elements, adapted for computer-aided design, such as information for
 determining represented dimensions, may be generated.
 Further, the transformed group of information elements, as initially set
 forth, may also be tested against recognized patterns for information
 elements, for a match for classification purposes, with such recognized
 patterns including patterns representative of a line and a 45-degree arc.
 In accordance with aspects of the invention pertaining to dividing a
 drawing stroke into parts or elements, a computerized method is provided
 for generating information representative of a drawing path lacking in
 certain precision criteria and selecting break information representative
 of breaks for segments of the drawing path. Indicator information elements
 representative of locations of movement of an indicator in a path lacking
 in certain precision criteria, are generated. Information elements are
 then classified in categories in response to classification standards. And
 break information elements are selected in response to the classifying and
 to break selection standards. The break information elements are to
 delineate limits for segments of information elements.
 In performing the classifying of information elements, functions
 representative of a change in angle, of curvature, and of a change in
 slope for information elements are calculated, and the information
 elements are categorized in response to the calculating. Categorized
 information elements may then be re-categorized in response to the
 categorizing for adjacent information elements, achieving the
 initially-referenced classifications for information elements.
 In the selecting of break information elements, potential break information
 elements may initially be selected in response to the initially-described
 classifying and in response to potential break information standards, and
 then information elements that are adjacent to potential break information
 elements may be operated on using a neural net. Potential break elements
 may then be eliminated in response to the neural net.
 The segments of information elements may be adapted to represent locations
 which in turn are representative of a path including curved open and
 closed segments, or a path including straight and curved open segments.
 In accordance with yet other aspects of the invention pertaining to both of
 the above aspects as well as to additional geometric constraint aspects, a
 computerized method is provided for generating information representative
 of a drawing path lacking in certain precision criteria and for
 transforming the information to a display representative of a drawing path
 not lacking in such precision criteria. Indicator information elements
 representative of locations of movement of an indicator in a path lacking
 in certain precision criteria, are generated. Break information elements
 to delineate limits for segments of information elements are defined in
 response to the generating. Modified groups of information elements
 representative of segments of a modified path not lacking in the precision
 criteria are defined. Geometric constraints among the modified groups of
 information elements are generated, and constrained groups of information
 elements representative of geometrically constrained segments are defined
 in response to the generating of the geometric constraints. Then a display
 is provided which is representative of a path not lacking in the precision
 criteria, and which is represented by information elements including the
 constrained groups of information elements.
 The geometric constraints, for example, can include coincidence,
 parallelism, tangency and relimitation.
 Additionally, information associated with the constrained groups of
 information elements for computer-aided design, including information to
 determine represented dimensions, can also be generated.

DETAILED DESCRIPTION
 As indicated, detailed embodiments of the invention are disclosed herein.
 However, embodiments may be provided in accordance with various forms,
 some of which may be rather different from the disclosed embodiments.
 Consequently, the specific details disclosed herein are merely
 representative, yet in that regard are deemed to provide the best
 embodiments for purposes of disclosure and to provide a basis for the
 claims herein which provide the scope of the present invention.
 There is shown in FIG. 1 a workstation 30 for computer-aided design (CAD).
 Among the components of the workstation are a standard mouse 32 which can
 be moved and otherwise operated by the user as an input device for the
 workstation, a keyboard 34 and a display 36 having a display screen 38.
 The workstation 30, of course, has the physical outward appearance of a
 conventional workstation. However, the internal workings, the interactions
 with the user and mouse, the results in providing computer-aided designs
 and drawings, and the computerized information associated with such
 designs and drawings, are in accordance with and incorporate the present
 invention.
 FIG. 6 illustrates the mouse 32 as moved along a drawing path shown by a
 line 40. As with typical drawing paths resulting from the free-hand
 movement of an individual, the drawing path 40 lacks the standards and
 precision criteria normally associated with formal drawings, particularly
 those for use in the design of products and parts. Thus, although the user
 probably intended to follow the path of a straight, angled line, the path
 actually followed significantly departs from this standard. The beginning
 of the path could typically be indicated to the workstation by the user
 pushing down a button on the mouse, indicating the start of an intended
 path. And the end of the intended path could typically be indicated by the
 release of that button, or the re-pushing of the same button after its
 prior release, or the pushing of another button after the prior release of
 the first. The path, from the start to end, would then be typically
 considered a path stroke, in a fashion analogous to a stroke of a pencil
 or pen by an individual executing a drawing.
 The series of crosses 42 shown on the display screen 38 of FIG. 6, then,
 represents, in illustrative form, the series of cursor positions on the
 display screen caused by the user's operations with the mouse 32.
 Similarly, the series of lighted locations 44, on the display screen,
 correspond to the series of cursor positions. Such lighted locations, of
 course, are typically denominated "points" on the display screen. Those
 points, if connected, represent a continuous path along the display
 screen. And assuming the workstation 30 and the display 36 having the
 display screen 38 (FIG. 1) have a fine enough resolution, the series of
 lighted points would typically have the appearance of a connected path to
 the user. The lighted series of points or locations 44, thus, represents a
 drawing path on the display screen 38 which corresponds to the drawing
 path 40 for the mouse 32. The series of points or locations, and the
 display path they represent, then similarly are lacking in the standards
 associated with a formal drawing.
 In FIG. 6, the designation I.sub.1 (X.sub.1,Y.sub.1) represents an
 information element provided internally by the workstation computer
 apparatus which represents the first point or location of the series of
 lighted points 42. The X.sub.1 and Y.sub.1 components of the information
 element are intended to schematically represent the location itself, for
 example the coordinates in a Cartesian coordinate system. A readily
 apparent alternative, of course, would be an angle and a radius in a polar
 coordinate system.
 There, then, of course is such an internal information element for each of
 the points, as indicated by the dotted line from I.sub.1 (X.sub.1,
 Y.sub.1) to I.sub.n (X.sub.n,Y.sub.n), a designation which represents the
 internal information element provided in the computer apparatus for the
 last point in the series of points 44. Again, the indicated designations
 are simply to represent information elements of the type typically used
 and employed in CAD systems.
 Still referring to FIG. 6, there is shown at the right, a series of lighted
 locations or display points 46 which is a similarly illustrative, modified
 version of the input or indicator series of display points, as a result of
 the method described herein. These display points are representative of a
 display path which has been modified to conform to a straight, angled line
 not lacking in the standards or precision criteria previously
 mentioned--i.e., a straight line according to the standards and criteria
 of a formal design drawing. The modified display path which these points
 represent, then, is a "fixed up" version of the path 40 along which the
 user moved the mouse 42. The output designations O.sub.1 (X.sub.1,
 Y.sub.1) through O.sub.m (X.sub.m,Y.sub.m) represent the information
 elements internally provided in the computer apparatus representative of
 the locations for the modified series of points or locations, determined
 in the computer apparatus.
 Standard CAD systems and methods provide design and relationship
 capabilities for executing and relating detailed designs, drawings and
 views. As several examples, this includes some capabilities to
 automatically take account of changes in related views and to maintain and
 indicate dimensional information. The designations D.sub.1 through
 D.sub.m, associated with O.sub.1 (X.sub.1,Y.sub.1) through O.sub.m
 (X.sub.m,Y.sub.m) in FIG. 6, are simply to indicate the existence of
 information elements in the computer system to carry out such standard CAD
 capabilities. And the presence of the dimensional representation of "L
 in." in an arrowed configuration between endlines, as part of the display,
 indicating the length of the straight line path represented by information
 elements O.sub.1 (X.sub.1,Y.sub.1) through O.sub.m (X.sub.m,Y.sub.m), is
 simply illustrative of such standard dimension-related capabilities.
 Referring to FIG. 7, the workstation 30 in accordance with the invention
 can generate information elements, representative of locations (or points)
 which are representative of a single point, a straight line, an open arc,
 a circle, or an ellipse, lacking in precision criteria or standards for a
 formal design or design drawing, and define a modified group of elements
 which are representative, respectively, of such geometric elements (or
 segments) with such precision criteria or standards not lacking. Such
 resulting segments are illustrated by the precise-appearing point 50,
 straight line 52, circle 54 and ellipse 56 shown in FIG. 7.
 In FIG. 10, a drawing path 60 for the mouse 32, intended as a straight
 line, but lacking in the precision criteria, is shown at the left.
 Alternatively, this path could be considered to illustrate the path that
 would be represented by the indicator information elements that would be
 generated in the computer apparatus of the workstation to correspond to
 the path of the mouse or indicator, or such a path as displayed. At the
 right, a drawing path 62 which is represented by modified information
 elements provided in the workstation 30 is shown. This, of course, has the
 appearance of a straight line embodying the desired precision criteria.
 Analogously, such paths for an intended arc 64, an intended circle 66, and
 an intended ellipse 70 lacking in the precision criteria, are respectively
 shown at the left in FIGS. 11, 12 and 13, while drawing paths for an arc,
 a circle and an ellipse having the precision criteria are, respectively,
 shown at the right in FIGS. 11, 12 and 13.
 The paths in FIGS. 10 through 13 are each for single-segment (or
 single-element) strokes. Thus, the workstation can recognize, categorize
 and operate on a straight line segment, an arc, a circle and an ellipse,
 as a single defined geometrical segment or element. The same, of course,
 applies for a point.
 In FIGS. 14 and 15, paths for multi-segment strokes are illustrated. At the
 left in FIG. 14, is a path 78 analogous to the paths at the left of FIGS.
 10 through 13, but for a stroke which is intended to be two straight line
 segments which come together at a corner break. In this case, the
 workstation 30 does recognize the intended corner break, indicated by the
 small circle 80. This entails the identification of an information element
 in the computer representative of a break location or break point. The two
 segments in the stroke having a junction delineated by that break point
 can then be separately recognized as straight lines and treated
 separately, except for the common break point. The result is a path 82
 incorporating, with the desired precision, two straight line segments
 joined in a corner break at 84.
 In somewhat analogous fashion, in FIG. 15 at the left, there is a stroke
 path 86, recognized as incorporating two break points, as indicated by the
 small circles 90 and 92. Here, two information elements representative of
 the locations or points for these breaks are identified. And the path is
 recognized as a three-segment path, including two straight lines joined by
 an arc, in a fillet configuration. The three segments, once the breaks are
 identified, can be recognized and treated separately to then together
 define information element segments representative of the three-segment
 path 94, having breaks 96 and 98, shown at the right in FIG. 15.
 In FIG. 8, there is shown, at the left, a typical mouse path 100 for an
 areafill command symbol. This can also be considered as the path which is
 represented by the indicator information elements which are generated by
 the movement of the mouse as the path indicator, or such path as
 displayed. At the right, is the analogous situation, but for the path 101
 for a delete command symbol. As indicated, if these symbols were used as
 components in a geometric path being constructed, they would typically be
 considered multi-segment (or element) strokes. But due to their
 distinctive natures, and the nature of the geometric path components which
 are recognized and allowed, these command strokes are ultimately treated
 as single whole segments or elements in connection with the recognition
 and use of the areafill and delete commands.
 In FIG. 9, at the left, there is shown a display screen path 102 for a
 square which has been subject to the precision enhancement, and a display
 path 103 for an areafill symbol corresponding to an areafill movement of
 the mouse 32. The result, a cross-hatched fill 104 of the area within the
 square, at the general angle of the areafill symbol, is shown at the
 right.
 In FIG. 16, a display drawing path 110 corresponding to a mouse drawing
 path which is intended to be a square is shown at the left. The arrows
 along the path indicate the direction of movement for the single stroke
 path. As indicated, true parallelism for the opposite sides of the path is
 lacking. Additionally, at the beginning and end of the path, there are
 extensions beyond a true corner location. This path, of course, could also
 be considered as illustrative of the mouse path itself. And the indicator
 information elements generated in the CAD workstation 30 (FIG. 1), of
 course, resulting from the mouse path, are representative of this display
 drawing path. The path 111 at the right, of course, reflects the
 capability to locate breaks, to recognize intended straight lines, and to
 generate modified information elements for such lines. However, it also
 reflects the capability to provide constrained information elements,
 reflecting the intended parallelism constraint between the pairs of
 opposite sides, and also reflecting relimitation constraints. At the
 right, in FIG. 16, the relimitation constraints are reflected in the
 relimitations of the sides of the square which come together at the start
 and end of the path so that the extent of each is limited to provide a
 corner at the lower left. The path 111 can be viewed as a path represented
 by the information elements provided in the computer system which
 incorporate all of the referenced aspects, including the constraints, or
 such path as displayed.
 In FIG. 17, such parallelism and relimitation constraints are illustrated,
 as well as tangency constraints. Display paths resulting from mouse paths
 (or what could also be viewed as the mouse paths themselves), are
 illustrated by the arrowed paths in the first, third and fifth frames of
 the figure. The non-arrowed display paths reflect, as needed, the break
 recognition, segment recognition and treatment, and the constraint
 recognition and treatment capabilities. These, of course, can also be
 regarded as the paths represented by information elements which have
 undergone the modifications or transformations to accomplish the
 corresponding aspects.
 Thus, in the first panel of FIG. 17, there is a single stroke drawing path
 112. In the second panel, that path has been converted to a path 114
 reflecting two straight line segments which are joined at a corner and
 which are at an angle to one another of somewhat greater than 90 degrees.
 In the third panel, another path 116 has been added as a result of
 movement of the mouse. That additional path indicates that it was the
 intent of the user to draw a square using two strokes. The parallelism
 constraints related to the opposite sides and the relimitation constraints
 related to where the strokes cross, are recognized, and they are reflected
 in the square path 118 of the fourth panel of the drawing. That path, of
 course, also reflects that the new drawing path added in the third panel
 was recognized as two straight lines which come together at a corner
 break. In the fifth panel, additional movement of the mouse has added a
 single stroke path 120 which was intended to be a circle within the
 square, tangent to each of the four sides. In providing this result, in
 the sixth panel, the new path has been recognized as an intended circle,
 and the tangency constraint between the circle and each of the four sides
 of the square has been recognized and is reflected.
 FIGS. 18 through 20 also illustrate geometrical constraints. Without the
 tangency constraint, a stroke intended to be a straight line, followed by
 a stroke intended to be a circle might be displayed as a straight line
 path 122 and a non-intersecting circle 124, as at the left in FIG. 18.
 However, due to the tangency constraint, an intended tangency relationship
 is recognized. The result is a straight line path 126 and a circular path
 130 that are tangent to one another. Analogously, without the coincidence
 constraint, the result might be a separated point 132 and straight line
 134 at the left in FIG. 19. With the coincidence constraint, the result is
 a point 136 which is coincident with a straight line 138.
 In FIG. 20, the tangency constraint is illustrated for a single stroke
 display path which was intended to be a circle and a tangential line
 extending from the circle. The display path 140 in which the circle is
 lacking in precision standards, the straight line is lacking in precision
 standards, and the tangency does not quite exist, is reflected at the
 left. At the right, there is the altered display path 142 including the
 circle and the tangentially extending line.
 The flow diagrams of FIGS. 2 and 3 are directed to the method for
 determining break locations to delineate segments for a stroke. The flow
 diagram of FIG. 4 is directed to the creation of segments embodying the
 desired precision standards from segments which lack such standards. And
 the flow diagram of FIG. 5 is directed to the more comprehensive method
 which incorporates the aspects of FIGS. 2, 3 and 4, as well as geometrical
 constraint aspects.
 Turning to the recognition of breaks to delineate segments in
 multiple-segment strokes, for the indicator elements which are generated
 in the computer apparatus in response to the movement of the mouse 32
 (FIG. 1 and FIG. 6), of course, each includes a representation for a
 location or point. Once this location or point stream is stored in the
 computer, through the stored indicator elements, the break location
 recognition (break point recognition) can start with operations that can
 be described as directed to the calculating of geometric characteristics
 which are applied to the points of the stream, and the filtering of the
 point stream.
 In carrying this out, the relative distance and angle (meaning change in
 angle) between pairs of points in the point stream for a stroke, as
 represented by the indicator information elements, are calculated. Thus,
 referring, for example to the second, third and fourth points for such a
 stroke, the distance which the second point is from the first point is
 calculated, the distance of the third point from the second is calculated,
 and the distance of the fourth point from the third is calculated.
 Similarly, the difference in angle of the line between the third and
 second point, and the line between the second and first point is
 calculated and applied as the change in angle applicable to the second
 point. And the change in angle of the line between the fourth and third
 point, from the line between the third and second point, is calculated and
 applied as the change in angle applicable to the third point. This is
 carried out for all the indicator element-represented points in the
 stroke, except as is readily apparent, there can be no change in angle
 applicable to the first and last points and no distance applicable prior
 to the first point or after the last point. This is as indicated at the
 start of the flow diagram of FIG. 2A (Block 144).
 Although settings could be made to require a minimum distance movement and
 minimum time interval, beyond such intervals resulting from the normal
 communication delays within the parts of the workstation 30 itself, from
 one indicator element generated in the computer apparatus to the next, it
 has been found advantageous to not require such minimal intervals, but in
 effect to allow the position of the mouse to be sampled generally as often
 as the workstation can do so. As a result, there can be duplicate
 indicator points represented by the indicator information elements in the
 computer apparatus. These duplicate points may be considered surplus
 information. And other surplus information or noise, of course, will
 typically exist.
 Therefore, consecutive duplicate points (which of course could be within a
 tolerance) as represented by the indicator information elements are
 eliminated from the stroke as stored in the workstation (Block 146). Then,
 as a noise removal aspect, within a tolerance, combinations of two and
 three consecutive angles applicable to consecutive points are tested to
 see if they will cancel out, and thus can be set to zero, as more or less
 representative of unintentional "wiggling" of the mouse by the user as the
 mouse was used (Block 150). For example, a series of changes in angle
 applicable to points, of 5,10, -15, 20, 5, 5, 10, -10, 0, is altered to
 changes in angle of 0, 0, 0, 20, 5, 5, 0, 0, 0. (This, of course, does not
 however mean that the information elements for these points are altered to
 somehow take account of this.) The units for these changes in angle might
 typically be representative of degrees of angle. Of course, these
 operations are part of the calculating of geometric characteristics and
 the filtering, for break recognition, referred to above.
 As a continuation of this process, radii of curvature applicable to points
 for the stroke, except for reasons which will become clear, points at the
 beginning and end, are calculated based on constructed circles for the
 points (Block 152). As indicated, this is done after the duplicate points
 have been removed but any cancellation of changes in angle, of course,
 does not affect the actual underlying points. Concerning this calculation
 of radii of curvature, except at the beginning and end to which this
 cannot apply, a radius of curvature is calculated for each point based
 upon a circle constructed by using that point, one located six points
 preceding it, and one located six points postceding it. Thus, by way of
 example, given the points p.sub.1, p.sub.2, p.sub.3, . . . , P.sub.n, the
 radius of curvature applicable to point p.sub.7 is determined by
 constructing a circle through points p.sub.1, p.sub.7 and p.sub.13. And
 the radius of curvature applicable to point p.sub.8 is determined by
 constructing a circle through point p.sub.2, p.sub.8 and p.sub.14. (This
 radii of curvature information is normalized to remove scale factors which
 may have been entered by the user to change the particular scale that
 might apply to a display of what is represented in the computer system at
 this point.)
 After this, for consecutive pairs of the centerpoints for the curvature
 circles that have been found, the distances between such centerpoints are
 calculated (Block 154). (Again, this is normalized to eliminate scale
 factors which may have been imposed in a particular display for the user.)
 Then, after that, an averaged slope which is applied to each point but the
 first three and last three, is calculated and applied to the points for
 the stroke (156). The calculation is done by finding the slope of the line
 defined by a point three positions preceding and three positions
 postceding the evaluation point. By way of example, given the points
 p.sub.1, p.sub.2, p.sub.3, . . . , p.sub.n, the slope for the point
 p.sub.4 is determined by constructing a line through the points P.sub.1
 and p.sub.7. The slope for the point p.sub.5 is determined by constructing
 a line through the points p.sub.2 and p.sub.8.
 This is then followed (at Block 158) by the use of the averaged slopes that
 have been calculated for points in calculating changes in averaged slope
 which are applicable to points. The change in averaged slope applicable to
 a point is calculated by determining the difference between that point's
 calculated averaged slope and the calculated averaged slope for the prior
 point. Of course, this will exclude the three beginning and three end
 points.
 This concludes what may be considered the part of the break recognition
 process which is directed to calculating geometric characteristics and
 filtering.
 The next set of operations is conveniently regarded as the aspect directed
 to classifying the regions of the stroke.
 In doing this (at Block 160), a category is applied to the points for each
 of the absolute value of the change in angle applicable to the point, for
 the curvature which is applicable to the point, and for the absolute value
 of the change in slope which is applicable to that point. The categories
 can be conveniently regarded as an attempt to categorize the region in
 which the point occurs based on the indicated variable. The categories are
 then regarded as the following:
 1. Solid Line--indicative of very linear;
 2. Mixed Line or Moderate Line--indicative of moderately linear;
 3. Mixed Curve or Moderate Curve--indicative of moderately curved;
 4. Solid Curve--indicative of very curved; and
 5. Sharp Turn--indicative of an extreme or severe turn.
 Continuing with the accomplishing of this categorizing, the following
 values are designed as limit values for what can be regarded as the
 following descriptive designations:

CHANGE IN CHANGE IN
 ANGLE CURVATURE SLOPE RESULT
 Solid Line Solid Line Solid Line Solid Line
 Solid Line Solid Line Mixed Curve Mixed Line
 Solid Line Solid Line Solid Curve Mixed Curve
 Solid Line Solid Line Sharp Turn Sharp Turn
 Solid Line Solid Curve Solid Line Mixed Curve
 Solid Line Solid Curve Mixed Curve Mixed Curve
 Solid Line Solid Curve Solid Curve Mixed Curve
 Solid Line Solid Curve Sharp Turn Sharp Turn
 Mixed Curve Solid Line Solid Line Mixed Line
 Mixed Curve Solid Line Mixed Curve Mixed Curve
 Mixed Curve Solid Line Solid Curve Mixed Curve
 Mixed Curve Solid Line Sharp Turn Sharp Turn
 Mixed Curve Solid Curve Solid Line Mixed Curve
 Mixed Curve Solid Curve Mixed Curve Solid Curve
 Mixed Curve Solid Curve Solid Curve Solid Curve
 Mixed Curve Solid Curve Sharp Turn Sharp Turn
 Solid Curve Solid Line Solid Line Mixed Line
 Solid Curve Solid Line Mixed Curve Mixed Curve
 Solid Curve Solid Line Solid Curve Mixed Curve
 Solid Curve Solid Line Sharp Turn Sharp Turn
 Solid Curve Solid Curve Solid Line Mixed Curve
 Solid Curve Solid Curve Mixed Curve Solid Curve
 Solid Curve Solid Curve Solid Curve Solid Curve
 Solid Curve Solid Curve Sharp Turn Sharp Turn
 This chart thus shows how the composite category applicable to a point is
 determined from the category applicable to the point for the change in
 angle, curvature, and change in slope variables. With regard to this chart
 and FIG. 2A (at Block 164), it should be noted that the sub-categories for
 different Line classifications, nevertheless, are Line classifications.
 Similarly, the sub-classifications for different Curve classifications,
 nevertheless, are all Curve classifications.
 Still as part of this aspect of classifying regions of the stroke, where
 there are "outlyer" points that are clearly anomalies within series of
 points, it is preferable that they be re-categorized (Block 166). This
 would apply to a single curved point found within a long stream of very
 linear points, with its re-categorization to a linear point. Similarly,
 indeterminate points are preferably categorized based on adjacent points.
 (As already indicated, this would include a number of points at the
 beginning and a number of points at the end.)
 After this classification aspect is carried out, the aspect directed to the
 identification of break point candidates (at Block 170 in FIG. 2B) can
 occur. This aspect includes features directed to the fixing up of point
 categorizations for break point identification purposes, the finding of
 corner break candidates, and the finding of fillet break candidates. These
 will all be treated in additional detail below in connection with FIG. 3.
 However, still referring to FIG. 2B (at Block 172), there are also
 operations directed to the testing and removal of break point candidates
 using segment analysis.
 This involves, how part of the stream of points which, presumptively, would
 be broken into two segments for treatment and recognition in accordance
 with the operations of FIG. 4, might test as a potential single segment
 under those operations with the point which has been identified as the
 candidate break point removed. This, of course, will be understood in more
 detail in connection with the description of the operations set out in
 FIG. 4, regarding the treatment of individual segments.
 Then, again referring to FIG. 2B (at Block 174), after potential break
 point candidates may have been removed, the true break points remain. And
 going back to the points or locations initially stored in the computer
 apparatus as a result of the movement of the mouse (in the form of the
 indicator information elements representing points or locations), without
 any of the changes or modifications which have been described in
 connection with the break point identification (apart from the removal of
 points which are removed candidate break points and the removal of
 duplicate points), the resulting segments in the stream of points, have
 been delineated by the final selected break points, and these segment
 streams of points (in the form of indicator information elements) are
 constructed and stored as the resulting segments for the stroke.
 Turning to FIG. 3, and the fixing up of point categorizations, the finding
 of corner break candidates, and the finding of fillet break candidates
 referred to only generally, above, such fixing up can occur (at Block 176)
 by a re-categorization of a number of points for break point candidate
 identification purposes.
 Initially, if the composite categorizations for all the points in the
 stream are curved, neither such re-categorization nor the finding of break
 points, corner or fillet, is required at all. It should be borne in mind,
 in this connection, that a Sharp Turn composite classification, is
 considered a Curve classification for this particular purpose. So the
 distinction between these two classifications, for this purpose, is not
 important. It should also be borne in mind that this also implements the
 condition, noted elsewhere, that a delete symbol is a single segment
 stroke.
 So, assuming all of the points are not curved, the operation directed to
 the re-categorizing (Block 176 in FIG. 3) is undertaken. One form of
 potential re-categorization, relates to Sharp Turn regions. An example of
 such a region would be a series of composite classifications for a series
 of points as follows: Line, Line, Curve, Curve, Curve, Sharp Turn, Sharp
 Turn, Sharp Turn, Curve, Curve, Curve, Line, Line.
 Typically, in a situation such as this, the Curve points immediately
 bracketing the Sharp Turn region are not really curved. There simply is a
 gray area in the transition from one Line region to another Line region.
 So, in a situation such as this, the classifications for these points are
 converted to Line classifications, so the series would be: Line, Line,
 Line, Line, Line, Sharp Turn, Sharp Turn, Sharp Turn, Line, Line, Line,
 Line, Line.
 However, in a situation such as this, it is possible that the Curve region
 is not merely a gray area (i.e., the user has drawn a line, followed by an
 arc at a sharp angle to the line). To accommodate this, only a limited
 number of point classifications are converted on either side of a Sharp
 Turn region. A limit of nine has been found convenient and effective.
 Although in the specific example, there are three consecutive points that
 are Sharp Turns, a single Sharp Turn point is sufficient to set in motion
 the re-categorization of Curve points on either side of the Sharp Turn
 point.
 Another re-categorization operation (Block 176) occurs where a substantial
 number of consecutive points have a change in angle less than some minimum
 absolute value, for example 0.01 degree. In a circumstance such as this,
 all of such points in the region are re-categorized to Line. The chart for
 the composite classification results, provided above, reveals that it is
 possible for a point with a very small change in angle to have a composite
 classification of Curve. The indicated re-categorization simply recognizes
 that those classifications typically are noise, and should be corrected.
 Requiring a minimum of nine such consecutive points to undertake the
 re-categorization has been found convenient and effective.
 Still focusing on the re-categorization (Block 176), points having a
 composite categorization of Mixed Curve (Moderate Curve) but also having a
 very small change in angle, also are converted to composite
 classifications of Line. The same 0.01 degree cut-off has been found
 convenient and effective, for this.
 After any such re-categorizations, the actual selection of a candidate
 break point can start with the locating of a Sharp Turn region (Block 178
 of FIG. 3). Typically, again, there would at least be a short series of
 consecutive Sharp Turn composite classifications. However, only one is
 required.
 After the Sharp Turn region is identified, the points in that region along
 with the two points bracketing the region on either side (which then would
 not be Sharp Turn points) are considered together, and the point among
 these having the highest absolute change in angle value is found. That
 point, then, is set up as a candidate corner break point (Block 180).
 This, of course, is done for each Sharp Turn region.
 Turning to the identification of candidate fillet break points, which of
 course are break points related to a curved form of a turn rather than a
 corner form, Curve regions are identified and used in instances of
 attempting to locate fillet break points. Referring to this aspect of FIG.
 3 (Block 182), there is the operation directed to locating a Curve region
 and counting the points in the region. If the count is sufficient (a
 convenient and efficient number, as in the figure, is a count of at least
 ten), and the bracketing points for the region are categorized as Line,
 then candidate fillet break points are selected at the edge Curve points
 for each end of the region (Block 184). (A readily apparent alternative
 would be to select the edge Line points.) If the number of points in the
 Curve region is insufficient (for example, less than ten), but there are
 enough points for a candidate Corner break point (for example, at least
 two, as in the figure), then there is the potential for instead generating
 such a Corner break point (Block 186). In this circumstance, the point is
 found in the Curve region with the highest absolute value of its change in
 angle. If this value is above a certain minimum (for example, twenty-three
 degrees, as in the figure), then a candidate Corner break point is
 generated at this location (Block 186).
 Of course, from what has been described and shown (e.g., see FIG. 15), and
 with reference to FIG. 3, it should be apparent that a candidate fillet
 break point for a region of the fillet type is only generated at an edge
 which has a Line point adjacent. Therefore, it is possible that one or two
 candidates may be generated for such a region.
 Now that the identification of break point candidates (Block 170 in FIG.
 2B) has been described in additional detail with reference to FIG. 3, the
 testing and removing of break point candidates (Block 172 in FIG. 2B) will
 be further described.
 Initially, a juncture has been reached where, through the candidate break
 points, the stream has been delineated into candidate segments. However,
 as part of the break identification and selection procedure, the segment
 classification procedure, which will be described in more detail in
 connection with FIG. 4, is invoked to classify the various candidate
 segments delineated by the candidate break points. These candidate
 segments are based on the initial indicator element locations or points
 generated by the movement of the mouse 32. As a result of this, there may
 be parts of the stroke where this classification indicates that a line
 comes together with a line. Similarly, there may be a result which
 indicates that a line leads into an arc or circle or an arc or circle
 leads into a line. Another possibility is that an arc or circle leads into
 another arc or circle.
 Simply stated, the testing for the removal of break point candidates (Block
 172 of FIG. 2B) involves, with certain qualifications, the testing of
 adjacent segments of the types noted, according to that same segment
 classification procedure (FIG. 4), but with the break point for the
 intersection of the two segments eliminated. This is done to determine if
 the segment classification procedure will yield a valid single segment
 classification without the break point present. If so, the break point
 candidate, along with its indicator element, is simply eliminated for all
 purposes herein, to provide a single segment region in place of a
 two-segment region.
 Therefore, if the Line-Line regions can be classified as a single line,
 with the break point removed, that break point in fact is removed. If the
 regions identified as a line leading into an arc or circle, or an arc or
 circle leading into a line, with a pre-qualification standard, can be
 classified, with the break point removed, as a single arc or single
 circle, that break point is removed. The pre-qualification is that the
 ratio of the radius for the arc or circle region to the length of the line
 region should be greater than or equal to a certain minimum value, for
 this break point elimination to be considered. The reason for this is
 that, to some degree, relatively short lines leading into or off of an arc
 or circle should be permitted and not eliminated. Such a minimum value of
 three has been found convenient and effective. With regard to the
 candidate break point at the union of an arc or circle segment with
 another arc or circle segment, if, with the break point removed, the
 segment classification procedure for single segments will yield a single
 arc or single circle, that candidate break point is then removed.
 Now turning to the flow chart of FIG. 4, the operations there are directed
 to the recognition of the individual segments into which a stroke has been
 divided, or the recognition of the single segment if there are no
 divisions, and the creation of a point, straight line, arc or ellipse
 based on what occurs.
 The initial aspect of this can be conveniently referred to as the
 transforming/normalizing of the stream of x, y coordinates. As already
 indicated, although some "clean-up" changes may have been made in relation
 to the point stream in connection with the break determination aspect
 already addressed, here the stream of points is the stream of locations
 represented by the initial indicator elements which were generated in the
 computer as the immediate result of the movement of the mouse by the user
 (e.g., see FIG. 6). The exception is the elimination of points, and their
 indicator elements, that were removed candidate break points as just
 described. Also, as in break recognition, duplicate points are eliminated
 here.
 As a technical matter, it might be noted that the "fineness" or accuracy of
 designated locations, represented in the computer apparatus, in fact is
 limited by the characteristics of the workstation 30 (FIG. 1). In that
 regard, it should be noted that a display (such as the display 36 in FIG.
 1), and its interfacing components may well have a "fineness" or
 resolution capability which in fact is less than that of the part of the
 work station which receives input information, does calculations, and
 stores results. Therefore, the location information in the information
 elements may typically have a much higher degree of resolution than what
 is displayed on a display screen or in other types of display, such as a
 print-out.
 Returning to FIG. 4, as will become apparent from the description of the
 initial transforming/normalizing set of operations related to a segment,
 this set of operations will typically involve the rotating, scaling and
 translating of the points (locations represented by the indicator
 elements) for the segment under consideration, or the interruption of
 these operations while in process to reach a pre-classification of the
 segment as a point (Block 186 in FIG. 4).
 At the outset of this, a Closed flag, which is used to record whether a
 segment has been determined to be a closed segment (such as a circle or
 ellipse), or an open segment (such as an arc or straight line), is set to
 False. Then the set of points is operated on to rotate the stream such
 that the vector defined by the start and end points is along the X-axis
 (at zero degrees). Then the dimensions of the resulting segment, in the
 X-direction ("dx") and in the Y-direction ("dy"), are determined. And the
 distance between the start point and the end point is also calculated.
 The ratio of this distance to the diagonal for a minimum-maximum box
 ("min-max box") for the rotated segment, with the sides of the box
 parallel to the X-axis and Y-axis, is tested. This diagonal, of course, is
 the square root of ((dx).sup.2 +(dy).sup.2). If this tested ratio is below
 a certain threshold, then certain additional operations are performed. As
 for this threshold, it has been found advantageous to allow the user some
 freedom in selecting it. A threshold of 0.1 which might be used by a user
 considered an "expert" in making relatively accurate drawings, a threshold
 of 0.2 for a user considered "intermediate", and a threshold of 0.3 for a
 user considered a "beginner" have been found convenient and efficient.
 If the ratio is below the threshold, then the least square fit line for all
 the points of the segment is calculated, the stream of points is rotated
 such that this line is at zero degrees, and the Closed flag is set to
 True, to indicate that, at this point, the segment has been determined to
 be closed. The least square fit line, of course, is the line which
 minimizes the square root of the sum of the distances squared, between
 certain related points of the segment and line. Such a least square fit
 line, and its determination by regression analysis is well understood and
 commonly used in various mathematically oriented operations and
 disciplines.
 Independently of whether the ratio was below the indicated threshold, and
 of whether the operations dependent on such are carried out, there has
 been a rotation of the point stream--either such that the vector defined
 by the start and end points is along the X-axis (zero degrees), or such
 that the least square fit line is along the X-axis. In either case, the
 rotated segment is then scaled and translated to lie within an area of a
 predetermined size in the +X, +Y quadrant, which is located at the origin)
 (0,0). As an example, a grid size of one inch by one inch has been found
 convenient and efficient.
 In a qualification to what has just been described, if the dimensions of
 the segment, represented by (dx, dy) are sufficiently small, or stated
 another way, the min-max box within which the segment fits, is
 sufficiently small, the segment can be pre-classified as a point (Block
 186), and a number of operations (Part of Block 186, and Blocks 190, 192,
 194, 196 and 200) can be avoided. Of course, there may be a significant
 number of indicator information elements within this area, i.e., the user
 may have moved the mouse somewhat to indicate the point, but the
 determination has been made that what the user has done should be
 interpreted as a point.
 In fact, and as may be expected, it has been found convenient and efficient
 to allow point classifications only where a full stroke can initially be
 pre-classified as a point. Therefore, prior to the break recognition
 aspects, as addressed in FIGS. 2 and 3, it is convenient and efficient to
 test a stroke for segment pre-classification as a point in the manner just
 described (including with the elimination of duplicate points as under the
 break recognition operations). In accordance with this, the point
 pre-classification, and the point creation and related aspects (removal of
 created point) as explained below, of the operations of FIG. 4, need not
 be undertaken for segment recognition for a multi-segment stroke, but only
 in segment classification operations prior to break recognition. And if
 there is such a point pre-classification prior to break recognition, the
 point segment is created at that time, in the manner explained below
 without break recognition.
 The next set of operations can be conveniently referred to as creating an
 input pattern for the segment, for purposes of pattern recognition and/or
 for a neural net.
 For purposes of testing the information about the segment for
 classification purposes, the result of the rotated, scaled and translated
 stream of locations (points) which form the segment, is mapped into a grid
 of 100 locations, 10 locations by 10 locations (Block 190). This, if
 course, is to limit the input information for classification of the
 segment to a relatively manageable size. Thus, the input information is
 reduced down to information as to whether each of 100 locations is a "hit"
 or "miss" for that segment.
 In order to reduce the similarity of hit patterns for this ten-by-ten
 matrix, it is advantageous to purposely modify certain types of patterns
 in order to make them more distinct from certain other types of patterns.
 In accordance with this, if the segment has been recorded as Closed, the
 pattern of "hits" is translated to the top part of the grid (Block 192).
 An example of this is the translation represented immediately below, with
 the hits in the ten-by-ten grid represented by x's.
 ##EQU1##
 As indicated, this translation involved translating the hit pattern upward
 until a hit reaches the top row of the grid.
 Another such change, in order to simplify the process of distinguishing
 between different classes of segments, is to flip the hit patterns for
 segment patterns which appear to be indicative of "smiling" arcs to make
 the patterns "frowning" arcs. The goal is to make the arc patterns all
 "frowning" to facilitate their recognition. An example of this, analogous
 to the translation example represented above, is represented as follows:
 ##EQU2##
 Thus, if the start and end of the hit pattern for the segment are on the
 same row of the grid, and the start-end row is not on the first row, and
 also if there are not any hits above this start-end row, the pattern is
 flipped. More technically, this involves changing the pattern to a mirror
 image across the horizontal which bisects the pattern in the Y direction.
 (This is also indicated at Block 192 in FIG. 4.)
 With this accomplished, an attempt can then be made to do another
 pre-classification of the segment, through its grid pattern, as a line, a
 45-degree arc, or as an areafill symbol using pattern recognition
 operations (Block 194). The reason for this is that the grid patterns for
 these segment classifications can be readily recognized by "inspection".
 Specifically, a pattern to be classified as a straight line, should only
 have hits along the first grid row; a segment to be classified as a
 45-degree arc should only have hits in the first two rows of the grid, and
 an areafill "segment" should only have hits which fall along the top row
 of the grid pattern. Such patterns are represented below:
 ##EQU3##
 With regard to the areafill, it should be noted that such an areafill
 symbol should have been translated to the indicated top row due to its
 classification as a Closed segment. The distinction between the areafill
 and the straight line in what is shown above is indicative if how the
 translation and flipping of patterns operates to help in easily
 distinguishing between different segment classifications.
 Somewhat similar to the situation of point pre-classification, an areafill
 symbol in fact is not allowed as a multi-segment stroke. For these
 reasons, and other reasons of efficiency, if in the testing for a point
 pre-classification prior to break recognition, there is no point
 pre-classification, the operations in the parts of FIG. 4 leading to
 pre-classification as a line, 45.degree. arc or areafill, the creation of
 a line, arc or areafill based on such pre-classification, and related
 aspects (removal of created segment), are also carried out prior to break
 recognition operation. This both permits testing of a stroke as a "single
 segment" areafill symbol, and can add efficiency in the instance of other
 forms of pre-classification. However, contrary to the situation for
 pre-classification as a point, in multi-segment recognition for a stroke,
 these pre-classification and related aspects for a line and 45.degree.
 arc, of course, are also still carried out for multi-segment strokes after
 break recognition. In multi-segment recognition for a stroke, as
 previously indicated, such pre-classification and related aspects for an
 areafill symbol, however, would not be carried out.
 At this juncture, a pre-classification for any segment which is to be
 classified as a point, a straight line, a 45-degree arc or an areafill
 symbol should have been accomplished (the point and areafill aspect only
 applicable to segment recognition attempted for a complete stroke prior to
 break recognition). However, if there has been no such pre-classification,
 one would now be dealing with a segment after break recognition in
 accordance with FIGS. 2 and 3, and the question remains as to whether the
 segment is to be classified as an arc, a circle, an ellipse or a delete
 symbol. In order to accomplish this classification aspect, a neural net is
 used employing the 100 points of the grid as the input nodes (Block 196).
 The neural net is one developed according to standard and well known
 techniques which have been used for a number of years. It is a back
 propagation neural net, as indicated, having the one hundred grid
 locations as one hundred input nodes, having 12 hidden nodes, and six
 output nodes. The output nodes represent, according to the strength of the
 output at the particular node, a confidence level in terms of the relative
 "closeness", by comparison with the other five possibilities, of the grid
 pattern to that for a 90-degree arc, a 180-degree arc, a 270-degree arc, a
 circle, an ellipse, or a delete symbol. With reference to the selection of
 the alternative arc sizes for the output nodes, these alternatives are
 chosen with a view ultimately of not distinguishing, for a segment,
 between arcs of different sizes, but for distinguishing an arc, from a
 circle, an ellipse, or a delete symbol. An example of output percentages
 which might be represented by the output levels at the nodes of the neural
 net, is as follows: 90-degree arc--92%; 180-degree arc--20%; 270-degree
 arc--1%; circle--0%; ellipse--2%; delete--8%.
 Once the test results of the neural net exist, certain criteria must be met
 in order to achieve a classification (as opposed to a situation in which a
 determination is made and indicated that no classification for the segment
 can be achieved). As a general criterion, the top two classification
 candidates must have a combined percentage level of 50% or more. Then the
 following classification criteria are applicable to the 90-degree arc
 classification:
 1. Closed flag must be False. (The closed or open indicator, thus
 indicating an open segment).
 2. The percentage indicated for the 90-degree arc must be 80% or more, or
 the runner-up must be the 180-degree arc.
 Then the criteria applicable to classification as a 180-degree arc are as
 follows:
 1. Closed flag must be False.
 2. Percentage level must be 80% or more, or the runner-up must be the
 90-degree or 270-degree arc.
 For the 270-degree arc classification, the additional criteria are:
 1. Percentage level must be 80% or more, or the runner-up must be the
 180-degree arc or the circle.
 2. If the percentage level is less than 80% and the runner-up is the
 180-degree arc, the Closed flag must be False.
 And the classification criterion for a circle, is the following:
 1. Percentage level must be 80% or more, or runner-up must be 270-degree
 arc or ellipse.
 The classification criteria applicable to an ellipse are then the
 following:
 1. Closed flag must be True.
 2. Percentage level must be 80% or more, or runner-up must be a circle.
 Finally, the classification criteria applicable to the delete symbol are
 the following:
 1. Closed flag must be False.
 2. Percentage level must be 80% or more.
 3. There must be at least 15 points in the delete stroke (with the
 duplicate points eliminated).
 An additional operation applicable to the classification using the neural
 net permits a change in the classification as determined above from circle
 to ellipse or from ellipse to circle if the aspect ratio for the segment
 indicates this should be done (Block 200). Specifically, if a
 determination indicative of an aspect ratio is beyond a pre-determined
 limit, a circle classification will be changed to an ellipse
 classification. Alternatively, if the determination is less, an ellipse
 classification will be changed to a circle classification. It has been
 found convenient and efficient to have the user set this limit at 2.5 if
 the user is considered a beginner, at 2.0 if the user is considered
 intermediate, and at 1.5, if the user is considered expert, in executing
 drawings. The calculation can conveniently be the ratio of the larger of
 the difference in the X or Y values divided by the smaller of the
 difference in the X or Y values for the segment as rotated in the manner
 described above--the larger of this "dx" and "dy" divided by the smaller
 of the two. As described above, this rotation would be expected to be
 based on the least square fit line for a circle or ellipse. Of course, a
 calculation based on other "versions" of the stroke, indicative of an
 aspect ratio could, alternatively be employed, such as based on "dx" and
 "dy" values for the segment as represented on the ten by ten grid.
 Now, the segment of concern has been placed in the classification of a
 point, in one sort of pre-classification (Block 186), in the
 classification of a straight line, 45-degree arc or an areafill symbol, by
 pattern recognition, in another type of pre-classification procedure
 (Block 194), or placed in the classification of a 90-degree arc, a
 180-degree arc, a 270-degree arc, a circle, an ellipse or a delete symbol,
 using a third sort of classification procedure including the use of a
 neural net (Blocks 196 and 200). From this point, the information to
 actually create or define the segment in the computer apparatus can be
 undertaken (Block 202), with the qualification that such a segment can
 still be removed if it is tested and found to have a geometry which is
 extremely large or small, or a geometry which is very far from the origin
 (Block 204). As previously indicated, this could be occurring, based on
 pre-classification as a point, for a stroke prior to break recognition. It
 could be occurring for a line or 45.degree. arc for a stroke prior to
 break recognition, or in segment recognition after break recognition. And
 for other arcs, an ellipse or a circle, this could be occurring after
 break recognition.
 Referring to this, it is convenient to refer to an arc first. In that
 regard, the method herein creates arcs which are each limited to a part of
 a single circle--i.e., a circle having a single centerpoint and radius.
 Once the classification has been set as an arc, the degree-size
 classification that has been made is no longer of direct concern. The
 initial indicator information elements stored in the computer apparatus
 (the points they represent) are now used again, with duplicate points
 removed and with removed candidate break points also not present.
 Specifically, the location information for the first such recorded
 indicator information element is used as a first sample point for defining
 the circle used in creating the arc; the location information for the last
 such recorded element is used as a second sample point; and the location
 information for the information element which is at a number count
 half-way (or approximately half-way) between the first and the last, is
 used as a third sample point. Specifically, those three points define a
 centerpoint and a radius for the circle. And the extent of the arc is
 defined by the first point location and the last point location (Block
 202).
 One pre-condition for the creation of the arc is that the three sample
 locations cannot be co-linear nor can any two of the three be coincident.
 Another, in the nature of post-condition, is that if the arc created is
 greater than 330 degrees, the arc simply is closed to make a complete
 circle (Block 202).
 With regard to the removal of a created arc (Block 204), there is a removal
 condition based on the geometry being too far from the origin.
 Specifically, it has been found convenient and efficient to allow the user
 to specify a scale for a "model unit" such that one such model unit equals
 one inch (on a display), or such that 25.4 model units equals one such
 inch (in the sense that there are approximately 25.4 millimeters in an
 inch). Once this scale is determined by the user, if the centerpoint for
 the created arc is determined to be outside the area of 15,000 by 15,000
 model units, it has been found convenient and efficient to not maintain
 the created arc, but to remove it and regard it simply as an error
 condition.
 Additional such error conditions, for an arc, relate to what may be termed
 a distance tolerance. Specifically, if the distance between the endpoints
 of the arc, or if the radius for the arc, is less than a distance
 tolerance, i.e., "too small", an error condition similarly is deemed to
 exist (Block 204). It has been found convenient and efficient to permit
 the user to specify this distance tolerance based on whether the user is
 considered a beginner, an intermediate or an expert in executing drawings.
 Such a distance tolerance of 0.1, 0.2 and 0.3 model unit has been found
 convenient and effective for, respectively, the expert level, the
 intermediate level and the beginner level.
 Turning to the creation of a straight line, in this instance, the locations
 for the first and last indicator information elements (with duplicate
 points removed and with removed candidate break points not present)
 provide the sample points for creating the straight line. However, as a
 pre-condition to such creation, these two locations cannot be coincident.
 If they are, an error condition is determined to exist. Also, as
 post-conditions (Block 204), if either location is outside a 20,000 by
 20,000 model unit area, there is an error condition; and there is also an
 error condition if the length of the resulting line is less than the
 distance tolerance, i.e., "too small".
 Turning to the creation of a circle as a segment, a min-max box, of the
 type previously described (Block 202), is determined. The "centerpoint"
 (based on bisecting the sides of the box) for the box is selected as the
 centerpoint for the circle. And the average of the width and length
 dimensions of the box is selected as the diameter for the circle. With
 regard to the removal of the created circle based on extremely large or
 small geometry or geometry very far from the origin (Block 204), it has
 been found convenient and efficient to require the radius to be greater
 than or equal to the distance tolerance and less than 5,000 model units.
 Similarly, it has been found advantageous to require the centerpoint to be
 within an area of 20,000 by 20,000 model units.
 Turning to the creation of a point as the segment, the location specified
 by the initial indicator information element (with duplicate points
 removed, as in break recognition) is selected as the location for the
 created point. As previously indicated, there would typically be a number
 of information elements after the first one, with the point determination
 based on the minimal size of the dimensions for the stroke. For a point,
 there is a removal of the created point, and an error condition, if the
 selected point is outside an area of 20,000 by 20,000 model units (Block
 204).
 For the creation of an ellipse (Box 202), a min-max box, of the type
 previously described, is used in determining the centerpoint and the
 lengths for the major and minor axes. The centerpoint for the ellipse is
 the "centerpoint" for this box determined by the intersection of the lines
 bisecting the opposing sides, and the lengths of the major and minor axes
 are determined by the length and width of the box. To determine the angle
 for the ellipse, the angle of a least square fit line, of the type
 previously described, is used. It has been found convenient and effective
 not to adopt removal conditions for the created ellipse (Block 204).
 As previously indicated, points, deletes and areafills are single element
 strokes. An areafill is associated with a closed area (FIG. 9). The angle
 of the cross-hatching which results from an areafill can be determined by
 the angle for a least square fit line for the symbol. It has been found
 convenient and effective to select an angle which is closest to the angle
 of the least square fit line from among the following group: 0.degree.,
 30.degree., 45.degree., 60.degree., 90.degree., 120.degree., 135.degree.,
 150.degree., 180.degree., 210.degree., 225.degree., 240.degree.,
 270.degree., 300.degree., 315.degree. and 330.degree.. One readily
 apparent choice for associating the areafill with a selected closed area
 is the proximity of the location for the first indicator element (with
 duplicate points removed, as in break recognition) in the areafill symbol,
 to the closed area.
 For a delete symbol, one readily apparent alternative is to delete the last
 prior segment (or stroke) added by the user, with the qualification that a
 point is to be deleted before a non-point. Another alternative is to use
 proximity, e.g., proximity to the first indicator element (with duplicate
 points removed, as in break recognition) for the delete symbol, or to use
 proximity first, and the last prior segment alternative, only as a
 fallback.
 In FIG. 5, the aspects directed to the determination of breaks for a stroke
 in order to divide the stroke into segments, the recognition and creation
 of segments, and to the matter of constraints, are placed in their broader
 computer-aided design (CAD) context. Of course, the initial operations to
 which the figure is directed, are in accordance with what has been
 described in detail, including: a user drawing a stroke, with the
 indicator moved in a stroke (Block 206); the selection of the break
 locations (points), dividing a multi-segment stroke into separate segment
 regions (Block 210); the recognition of the multiple segments in the
 stroke (or, e.g., of the segment in a single-segment stroke) (Block 212);
 and the creation of the multiple segments (or, e.g., single segment)
 (Block 214).
 With the creation of these segments (of the information which defines these
 segments), the segments (information) can be added to the CAD model which
 is developed at the workstation (Block 214). Such a model, which is a
 standard in the CAD field, contains the information to define the design
 or work which is of concern.
 FIGS. 16 and 20, and the description in connection with such figures,
 illustrate the finding of constraints within the segments of a stroke.
 FIGS. 17, 18 and 19, and the description in connection with them,
 illustrate the finding and taking account of constraints between the
 segments of different strokes, i.e., of a newly generated stroke with the
 segments of a prior stroke or strokes. Such operations, of course,
 incorporate the finding of constraints, such as coincidence, parallelism,
 tangency and relimitation, within the created segments for a stroke,
 between such segments and those of prior strokes (Block 216), and the
 adding of the found constraints and the created segments to a constraint
 management system (Block 218) for the CAD system. Operations and
 techniques to find and determine such geometrical constraints in an CAD
 environment are the subject of an application by the present assignee,
 filed concurrently herewith, having Edward T. Corn as the inventor. That
 application, which is incorporated herein by reference, is entitled
 Automatic Identification of Geometric Relationships Between Elements of a
 Computer-Generated Drawing and carries Robbins, Berliner & Carson Docket
 No. 5908-102. Beyond operations and techniques relating to geometrical
 constraints just noted, that application is also directed to additional
 constraints, such as colinearity, perpendicularity, and same size.
 The constraint management system can then solve what the segments should
 be, consistent with the constraints (Block 220). Of course, this could
 typically include modifying the created segments somewhat in order to
 incorporate such consistency, and, also, modifying prior segments for the
 same reason. Once constraints are determined, the solving of segments
 consistent with such constraints is a more standard type of operation. A
 product sold by D-Cubed Ltd. under the name DCM is illustrative of
 programming/software for a workstation adapted to carry out such
 operations.
 Once segments are solved consistent with geometrical constraints, the
 segment information, as stored in the CAD model, can then be updated for
 the segments (Block 222). Then the model is up-to-date for any of its
 normal design or display functions, including the display of the updated
 segments (Block 224).
 The distance from the centerpoint for a constructed curvature circle
 applicable to an information element (or the location or point represented
 thereby), from a preceding information element is indicated as calculated
 in the preceding description (Block 154). Although not incorporated in the
 break aspects as previously described, modifications could be incorporated
 to use these center distances and to incorporate the use of inflection
 breaks, in addition to corner and fillet breaks. To do this, locations
 might be found that have relatively large values for this applicable
 center distance, as candidates for inflection breaks. These locations, as
 a prerequisite, should also be in a relatively small series of composite
 Line classifications, bracketed, on both sides, by fairly long series of
 curved composite classifications. An example of this could be:

Composite Classifications Center Distance
 Curve .1
 Curve .2
 . . . . . .
 . . . . . .
 Curve .1
 Curve .1
 Line 100.
 Line 50.
 Curve .2
 Curve .1
 . . . . . .
 . . . . . .
 Curve .1
 In this example, the inflection break or inflection break candidate would
 then typically be where the value 100 center distance occurs.
 Along similar lines, a variation on the steps to identify break point
 candidates, as outlined in connection with FIG. 3, may be considered
 advantageous in certain respects. Referring to this alternative, and again
 assuming that all points are not curved (in the manner previously
 described), at this juncture, which would avoid any break point
 identification, re-categorization operations can then begin under this
 alternative. And, again, here, one form of potential re-categorization,
 relates to Sharp Turn regions. Repeating the prior example, an example of
 such a region would be a series of composite classifications for a series
 of points as follows: Line, Line, Curve, Curve, Curve, Sharp Turn, Sharp
 Turn, Sharp Turn, Curve, Curve, Curve, Line, Line. But, in this case, the
 classifications for the Sharp Turn points are converted to Curve
 classifications, so the series would be: Line, Line, Curve, Curve, Curve,
 Curve, Curve, Curve, Curve, Curve, Curve, Line, Line.
 And, again, here, although in the specific example, there are three
 consecutive points that are Sharp Turn, a single Sharp Turn point is
 sufficient to set in motion the Sharp Turn point re-categorization.
 The re-categorization of a substantial number of consecutive points having
 a change in angle less than some minimum, to Line, and the
 re-categorization of Mixed Curve points also having a small change in
 angle, to Line, is then still performed.
 Then, for each former Sharp Turn, converted as above, the points that are
 now Curve points are considered together and the point among those having
 the highest absolute change in angle value is found. That point, then, is
 set up as a candidate corner break point.
 Then for the candidate fillet break points, their selection, based on Curve
 regions having sufficient Curve point counts, and having bracketing Line
 points (including regions having re-categorized Sharp Turn points), is as
 previously described. And, the potential selection of additional corner
 break points, if the number of points in the Curve region is insufficient,
 but sufficient for a candidate corner break point is as previously
 described.
 This, by contrast with the other approach, does not tend to wash out some
 potential candidate fillet breaks with corner breaks. It, however, also
 can typically create more candidate break points that are removed in the
 manner previously described to determine the final break points.
 It might be noted that although a mouse 32 has been shown and described
 herein as a convenient device for a user to employ in the interactions
 described, and particularly in indicating a user-controlled path, a
 variety of other conventional alternatives are readily available. One of
 these, of course, is a puck which is part of a digitizing tablet device.
 Many of the details included above, and how they are carried out, are
 particularly well suited to incorporation into CAD systems of Dassault
 Systemes of America Corp., which are marketed under the trademark
 PROFESSIONAL CADAM, for Unix Workstations of IBM sold under the model name
 RS-6000 or sold by Hewlett-Packard Company under the model number 700, and
 the operations are particularly well suited to implementation through the
 C++ language, or that language in combination with the C and Fortran
 languages.
 As will be readily apparent, various aspects, as described in detail
 herein, are exemplary, and readily subject to different choices and to
 change or modification, depending on the particular application, context,
 and requirements. Thus, many changes and variations may be made without
 departing from the scope or spirit of the invention.