Abstract:
A computer-aided process is disclosed for automatically generating a camera-ready hardcopy of a graphical plot upon command instructions inputted via a conventional storage tube graphics display terminal having an addressable cross-hair cursor and a keyboard. In accordance with an interactive graphics code or program, tabular data coordinates stored in computer file form are retrieved and plotted on appropriately titled and scaled axes with the plotted coordinates being interconnected along curves formed of a smooth or linear nature by interpolation. The graphical plot viewed on the display terminal is further enhanced by inclusion of labels, shaded areas, and reference symbols and characters prior to printing out the hardcopy of an associated hardcopy unit coupled to the display terminal.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     APPENDIX 
     An appendix consisting of 51 pages is included in this application. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to graphic arts in general and more particularly to an improved process for automatically generating camera-ready graphical artwork with the aid of a computer. 
     Graphical artwork, more specifically, graphical plots are commonly used as a visual aid to display a substantial amount of information regarding the coordinate relationships of certain variable physical quantities. In addition to the plotting of the basic coordinate data, typically for selected values of a variable factor or condition, such graphical plots generally include a variety of reference lines or curves as well as shading patterns for ready observation and interpretation of the data. Large quantities of these highly informative graphical plots, often found in scientific works and technical reports and manuals, are usually printed using conventional methods of photolithography that require production of a high-quality reproduction copy of the graphical plots in intricate detail, ready for photographing by a process camera. 
     Commonly known as being camera-ready, such high-quality reproduction copies of the graphical plots have been difficult and time-consuming to produce as well as to edit and correct if necessary. Hand-drawing and editing of the plots by skilled draftsmen, although satisfactory from a quality standpoint, continues to be painstaking and costly. Machine-drawn plots can be produced in substantially less time and have generally been adequate in quality and detail. However, such machine-drawn artwork still requires manual &#34;cut-outs&#34; and &#34;paste-ons&#34; to meet camera-ready requirements. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a main purpose and general object of the present invention to provide an improved process implemented by a computer for generating graphical artwork of a finished quality ready for photolighographic reproduction. 
     It is a more particular object of the present invention to provide a computer-aided process for producing original camera-ready graphical plots in full detail without requiring any manual drafting labor. 
     It is a further object of the present invention to provide an automated process for creating revised camera-ready graphical plots that permits custom editing and correcting of existing plots quickly and precisely without manually redrawing revisions and affixing those revisions to the existing plots. 
     It is a still further object of the present invention to provide a computer-aided process for graphical artwork generation that is cost effective, reliable in performance, and easily adapted to existing automated graphic art equipment. 
     Briefly, these and other aspects of the present invention are accomplished by a computer-aided process for automatically generating a camera-ready hardcopy of a graphical plot upon command instructions inputted via a conventional storage tube graphics display terminal having an addressable cross hair cursor and a keyboard. In accordance with an interactive graphics code or program, tabular data coordinates stored in computer file form are retrieved and plotted on appropriately titled and scaled axes with the plotted coordinates being interconnected along curves formed of a smooth or linear nature by interpolation. The graphical plot viewed on the display terminal is further enhanced by inclusion of labels, shaded areas, and reference symbols and characters prior to printing out the hardcopy on an associated hardcopy unit coupled to the display terminal. 
     For a better understanding of these and other aspects of the present invention, reference may be made to the following detailed description taken in conjunction with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a general block diagram showing the hardware used to implement the process for automatically generating camera-ready graphical plots in accordance with the present invention; 
     FIG. 2 is a general flow diagram of the computer-aided process of the present invention, showing the broad stages of data processing steps and their standard sequence; and 
     FIGS. 3A-3P, inclusive, represent a more detailed flow diagram of the computer-aided process in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, the process for automated graphics generation according to the present invention is primarily aided and implemented by a general purpose digital computer system 10 serving as the host and programmed to operate in accordance with an interactive graphics code, described in greater detail hereinafter. 
     It should be noted that the interactive graphics code, used by the host computer system 10 to interpret and perform the interactive requests of the user is also described in the Appendix, which is the source code listing of the interactive graphics code written in FORTRAN IV. This source code listing of the instructions, routines, and other contents of the interactive graphics code in appropriate sequence may be implemented, for example, on a CDC Cyber Model 175 computer using a FORTRAN computer CDC Version 438, a linker/loader CDC Version 1.5538 for Network Operating System (NOS) 1.4, and a library module TEKTRONIX Plot 10. 
     Stored with sets of tabular data coordinates in computer file form, digital computer system 10 is coupled to a conventional storage tube graphics display terminal 12 which accepts data from and sends data to the computer system. Display terminal 12 is equipped with a screen 14 on which output from computer system 10 is displayed to a user, the screen being the face of a storage tube device (not shown), typically a cathode ray tube (CRT), which maintains a display once written, for an indefinite period of time until an erasure is made. Display terminal 12 is further provided with a control panel 16 on which a keyboard 18 is located for allowing the user to enter alphanumeric (A/N) data onto the screen 14 and onto the computer system 10. A cursor control 22 also located on the control panel 16 is employed by the user to address a graphic cross-hair cursor 20 movable across screen 14 to specify positional input of data. The display terminal 12 with the aforedescribed features is a commercially available unit, one suitable such unit being the Tektronix Model 4015 with its associated graphics software. A conventional hardcopy unit 24 compatible with display terminal 12 is coupled thereto for producing, in accordance with the present invention, a camera-ready, hardcopy 26 of a graphical plot produced on the screen 14. 
     Referring now to FIG. 2, Block 31 represents a general start up procedure in which the user establishes communication with the host computer system 10 and commands use of old data files and eventually begins execution of the interactive graphics code. Block 31 is a query as to creating a new data file or using the old one. If the user&#39;s response is new data, then a query for axis labels and other minimum graphical data is indicated. In Block 31, the old data is automatically inputted into storage along with labels and other information. Block 33 is the top of the interactive loop in which the user physically moves the coordinates on screen 14 via cross-hair cursor 20 and keys a single character on keyboard 18. This single character and the coordinates comprise a user command. Block 33 additionally performs other data checks such as, if this is a new plot (no data to plot), a create line command is automatically executed. Block 34 checks for a valid command. An invalid command sends control back to block 33. Blocks 35 thru 38 interpret the command, use the coordinate data, if required, and act appropriately on the plot. 
     Three groups of commands are available: label, coordinate and plot. Block 36 only concerns labeling. Block 37 concerns only line forming, coordinate points and shading. Block 38 concerns the general plot attributes, such as size, grid and line types. Block 39 thru 46, inclusive, follow a command to plot the data. Block 39 uses the minimum and maximum data ranges and the grid requirements, and picks an appropriate scale on each axis, finally plotting the axis and labels. Block 40, besides plotting other labels, saves the four coordinate points around the label for later use. Blocks 41 thru 44, inclusive, are concerned with lines on the plot. Options are available for smooth curve, linear, or just symbols. In addition, lines can be one of 9 dash line types with options for solid thick or thin lines, as well as closed or open curves. Block 45 plots the grid as specified and uses the label coordinate point data generated in block 40 such that no grid line extends thru a label. Block 46 completes the plot by determining shading regions and plotting them with a uniform grid of dots again avoiding shading of labels. The end result of block 46 is that the user has on the screen 14 the latest edited plot. At this point control is transferred to block 33 for more editing or termination of the plot. 
     Referring now to FIG. 3A, in Block 50 the user turns on the display terminal 12, connects to the host computer system 10 and begins execution of the interactive graphics code. Block 51 prompts the user as to product and date of version of the graphics code. In addition, a query is issued for a communication transmission rate with the host computer system 10. In block 52, the user picks an appropriate code number 1-4, indicating the desired rate of character transmission or baud rate. For example, codes 1-4 typically designate baud rates of 1200, 2400, 4800 and 9600 characters per second, respectively. Block 53 checks the baud rate code and passes to block 54 if valid; otherwise, the process moves back to block 52. Block 54 makes a read attempt to determine if the user has connected through the host computer system 10 another file containing an old plot data set. Block 55 checks this read and if an end of file was found, then a new plot is implied and the user is prompted for minimum data (plot axis labels for storage) in block 57. Block 58 queries the user for decimal places for each data group. These data are those generated during the plot creation and used to generate a data file of the created plot for storage in the files of the host computer system 10. Blocks 59 and 60 check and query the user for these data. Referring back to the other branch of block 55, in block 56 old plot data is read from file storage and readied for use. Block 61 sets the communications transmission rate and the character size on the screen 14 of display terminal 12 to small. Block 62 begins the interactive plotting in subroutine TIGPPR. Block 63 sets the grid and range of data to either user input values or default. The default data range is the minimum and maximum values of the X and Y data, respectively. Block 64 initializes a set of points to the serial coordinate data forming a linked list. The linked list is used to efficiently add or delete a coordinate data point to a line or shaded area. Block 65 sets the graphics software associated with the display terminal 12 for use of stroke generated characters rather than a composite (one of four fixed size horizontal characters). This is required in order to generate labels at any size and rotation. Block 66 operates on the linked list, determines the number of lines and where each line begins in the linked list data storage. 
     Referring now to FIG. 3B, block 67 checks the number or coordinate points and, if it is zero (a new plot), the user is prompted and sent to the command mode. If data exists, then a check is made in block 69 to see if this data has been plotted once. If not, block 70 prints the main plot label and GRID/DATA range values. A window on screen 14 (physical plot size) is now set in block 17. Block 72 checks the validity of data ranges. If they are not valid, block 73 computes minimum and maximum values, respectively. Block 74 determines data scaling parameters from minimum and maximum X and Y values. The scales being preset to multiples of 1, 2 or 5. Block 75 computes the scaling of real units to the screen units, typically 4096×4096, on the display terminal 12. Block 76 checks for first time plot and gives the user a chance to change size, grid and other parameters. Blocks 77, 78 and 79 are reference to respective subroutines for drawing curves and labels, shown in greater detail in FIGS. 3L, 3M and 3O, respectively. Blocks 80 thru 83 determine if default axis labels are drawn, and draw all other labels using the subroutine PTITE, shown in greater detail in FIG. 3M. 
     Referring now to FIG. 3C, block 84 checks for existence of shading. If shading exists, then subroutine SHADIT, shown in FIG. 3P, is called in block 85. Similarly, both X and Y Grid requirements are checked and subroutines PGRIDX and PGRIDY shown in FIG. 3N are called as needed. Block 90 turns off the stroke characters since they are not needed in the command mode. 
     Referring now to FIG. 3D, in block 91, the user physically positions the movable cross-hair cursor 20 to a position on screen 14 after which a single character on keyboard 18 is depressed. The character depressed is used to determine the coordinate command and the position of the cross-hair cursor 20 on screen 14 used to compute a coordinate position X and Y. Block 92 checks for a valid command by performing a table look-up using the ASCII code for the character keyed. The ASCII is the American Standard Code for Information Interchange, a standard code consisting of 7-bit elements for information interchange among data processing communications systems. Block 92 flags the character as invalid, i.e. illegal, and re-prompts user in block 91. A valid coordinate command from the user continues the process as desired, and such valid commands are as follows: 
     
         ______________________________________VALID COORDINATE COMMAND SUMMARYCOMMAND  DESCRIPTION______________________________________A        add point after reference pointB        add point before reference pointC        identify closest data point (to cross hairs)D        delete data pointE        exitF        format (change line type)G        input grid dataH        halt graphics tablet modeK        kill line with closest data point to cross hairsL        ENTER label mode and locate closest label to    cross hairsM        MOVE identified data point to new positionN        input a new data point beginning a new lineP        re-plot the current data using same window scaleQ        quit label modeR        repeat the current data (but resize it to fill    screen)S        show real values X and Y at current    screen positionT        Enter graphic tablet modeV        input direct coordinate values for X and YW        Window data P replot to new minimum    and maximum values______________________________________ 
    
     The above coordinate commands, prefixed each respectively by the number &#34;9&#34;, are shown in FIGS. 3E, 3F, 3G, 3H, 3J and 3K and are described in greater detail hereinafter with appropriate reference to those figures. 
     Referring now to FIG. 3E, block 94 checks to see if this is the first point of a new plot; if it is, then control is transferred to the appropriate coordinate command for inputting a new line. The command &#34;A&#34; (99A) basically adds a point in storage after a reference point, the reference point being set by the command &#34;C&#34; (9C), shown in FIG. 3F. Block 95 checks to see if the user had set a reference point, a transfer to block 93 indicating a point not set and an invalid command. Block 96 checks to see if the point is within the plot frame on the screen 14 of display terminal 12. Block 90 plots a character indicating the line type at a coordinate position selected by the user. Block 98, using the linked list storage, adds the new point into the list after the reference point, and changes the reference point to the new point just added. Coordinate command &#34;B&#34; (9B), also shown in FIG. 3E, follows the same logic as the &#34;A&#34; command except as to placement of the new point relative to the reference point. Via block 103, the &#34;B&#34; command puts the point before the reference point in storage. The linked list is used the same way except the coordinate values are swapped so that the link list remains the same as in the A command mode. 
     Referring now to FIG. 3F, the &#34;C&#34; command (9C) establishes a reference point by finding the closes coordinate point per block 104. Blocks 105 and 106 check the point and plot a line character symbol if the point is within the plot frame. Block 107 moves the linked list forward pointer to the next set of coordinate points and stores the positions and line number of the reference point. The &#34;D&#34; coordinate command (9D), also shown in FIG. 3F, deletes a coordinate point and performs the same operations in blocks 108, 190 and 110 as the respective blocks 104, 105 and 106 for &#34;C&#34; command. The &#34;D&#34; command differs, however, from the &#34;C&#34; command in that in Block 111 the point is deleted from the linked list. This is accomplished by moving the forward coordinate set, as pointed to by the forward pointer, to the deleted point position. The unused data storage space is then added to another linked list which is a list of unused storage. Block 112 turns off the reference pointer flag since the point was just deleted. The &#34;E&#34; or exit coordinate command (9E) is executed per block 113 which terminates the plot, returns to the main program, and converts the linked data to serial data and outputs the data with all corrections, labels and arrows to the file of host computer 10. 
     Referring now to FIG. 3G, the &#34;F&#34; or format command (9F) can change the line characteristics in terms of linear, smooth, symbols only, no symbols, closed curve, or shade. The user positions the cross-hair cursor 20 either to the left or right of the vertical axis of the plot. Block 121 checks for this relative position of cursor 20. If the position is to the left, block 122 is used and the line type and curve type are changed for all lines of the entire plot. If the cursor position is to the right of the vertical axis, block 123 is used and the format change only applies to the indicated line. The lines and associated symbols are listed in a column at the left top of the terminal display screen 14. In block 115, the vertical coordinate position is used to determine the closest line and symbol. The line number is derived from this operation. Blocks 116, 117, 118 and 119 check that value and keep it within the range of one to the maximum number of lines plotted. Block 120 prompts the user for the new line type value and new curve type value. Blocks 121, 122 and 123, as previously discussed, determine how to apply new line type and curve type. 
     The &#34;G&#34; command (9G), also shown in FIG. 3G is executed via block 124 and is used to change the grid format. The user selects the number of major and minor tick marks and the frequency of grid lines on both axes. Via block 125 the &#34;H&#34; Command (9H) is effected. The &#34;H&#34; command is used to terminate the tablet command mode, the tablet mode being analogous to the screen mode in the context of the command and coordinate entry. The &#34;K&#34; or kill command (9K) is executed via block 126 and 127 and is similar to the &#34;D&#34; or delete command except that the &#34;K&#34; command deletes the entire line. 
     Referring now to FIG. 3H, the &#34;L&#34; command (9L) enters the label mode via block 128. The label mode keys a new set of single key commands which only affect labeling of the plot. The initial &#34;L&#34; command enters the label mode and uses the coordinate position to compute the closest label. The following is a summary of label mode commands: 
     
         ______________________________________LABEL MODE COMMAND SUMMARYCOMMAND    DESCRIPTION______________________________________L          Identify closest label and plot point showing      its reference pointM          Move identified label to indicated cursor      positionS          Change label sizeD          Delete labelQ          Quit label mode return to coordinate modeN          Add new label at current cursor positionA          Add arrow to plotP          Print current identified labelC          Copy identified label to new cursor positionV          Move label to new vertical positionH          Move label to new horizontal position______________________________________ 
    
     These label mode commands, like the coordinate mode commands, are prefixed by the number &#34;11&#34; for designation in the drawing figures and are described hereinbelow. 
     In accordance with the &#34;M&#34; label mode command (11M), the user moves an identified lable to a described position using cursor 20. The user is then prompted for two more coordinate points. These points are used to compute the slope of the label in block 131. The label is then printed at the indicated position along the new slope. Block 132 represents the &#34;S&#34; label mode command (11S) used to change the size of a label. Block 132 also checks to insure that a label has been identified using the initial &#34;L&#34; command. Block 133 executes the &#34;D&#34; label mode command (11D), deleting the previously identified label. The &#34;N&#34; label mode command (11N) executed via block 134 inputs a new label and its attributes, i.e., justification and storage. Block 134 also prompts the user for 2 additional points required for slope computation. In block 135, the &#34;A&#34; label mode command (11A) is implemented. The user positions the cursor 20 at the arrow tail (non-pointed end) and keys &#34;A&#34;. Two additional points are requested giving a broken arrow with the final point as the arrow head. 
     Referring now to FIG. 3I, block 136 affects a &#34;P&#34; or print label command (11P). In accordance with block 136, the current located label is re-printed. This provides a means for the user to identify which label is located when the initial &#34;L&#34; command is sued in clustered labels. Block 137 implements the &#34;C&#34; label mode command (11C), generating a copy of the identified label and promptly the user for two additional points to define the slope of the new copied label. The &#34;V&#34; label mode command (11V) implemented via block 138 is a quick label move to the indicated position, with the orientation vertical, reading from the bottom to the top on right side. Similarly, block 139 executes the &#34;H&#34; habel mode command (11H), performing an analogous label move, with the label set horizontal. Both the &#34;V&#34; and &#34;H&#34; label mode commands in blocks 138 and 139 are fast versions of the previously described &#34;M&#34; label mode command (11M). Block 140 represents the &#34;Q&#34; label mode command (11Q) that exits the label mode and returns the user to the coordinate command mode. 
     Referring now to FIG. 3J, the remainder of the coordinate commands are shown. In block 141, the &#34;M&#34; coordinate command (9M) is executed, moving the previously identified coordinate point to a position as indicated by cursor 20. Block 141 also checks to insure that a previous point has been identified as the reference point via the &#34;C&#34; coordinate command and block 104. Block 142 prompts the user for a new line value as well as line and curve type in accordance with the &#34;N&#34; coordinate command (9N). The coordinate point at the cursor 20 is identified as the first point of the new curve. In addition the reference point is automatically set to the new point. 
     The &#34;P&#34; plot coordinate command (9P) is executed in a series of steps represented by blocks 143-146. The first step of the &#34;P&#34; coordinate command, taken in block 143, is to determine the vertical position of the cross-hair cursor 20. If the position is to the right of the vertical axis, then control is transferred to block 65 to FIG. 3A, causing the graphics code to replot the data. If the cursor 20 is to the left of the vertical axis then further checks are performed. In block 144, a check is made to see if the line values and symbols have been already listed, i.e., in column format, left of vertical axis. Block 147 lists these line values and symbols if they have not been listed and in block 145 the line value of the closest line, listed in block 146, to the cursor 20 is determined. This closest line is toggled to plot in the next &#34;P&#34; command, and gives the user the capability to edit, plot and correct several lines overlapping on each other by plotting each one separately. The &#34;P&#34; command based on position of cursor 20 left of the vertical axis, can be thought of as a pick to live to plot command. In block 148 the &#34;R&#34; or restore/reset coordinate command (9R) is initiated. As with the &#34;P&#34; command and block 143, the vertical coordinate position of cursor 20 is used to determine the effect of the command. To the left of the vertical axis, the &#34;R&#34; command restores all lines to plot visibility. To the right, the &#34;R&#34; command resizes the plot to fit the minimum and maximum values contained within the coordinate data. In block 150, the &#34;S&#34; or &#34;show&#34; coordinate command is executed, the coordinate values being used to compute the actual real units at the cross-hair location of cursor 20 and these values being displayed on the screen 14. In block 151, the control is transferred, in accordance with the &#34;T&#34; coordinate command (9T), to the graphics tablet using a &#34;mouse&#34; to position and key coordinate commands. 
     In FIG. 3K, block 152 initiates the &#34;V&#34; coordinate command (9V). The &#34;V&#34; command is similar to the &#34;A&#34; or add point command except that the user directly inputs the exact values. Block 152 checks for a reference point and block 154 prompts the user for one set of coordinate values. Block 155 prompts the user to store before or after the reference point. Block 157 resets the new point to the reference point and transfers to the next command. Block 158 initiates the &#34;W&#34; or window coordinate command. In this command, the user is prompted for two sets of coordinate points from which a rectangular window is formed and the plot size enlarged to fill screen 14 with data in that window. Block 158 gets the first set of coordinate points and block 160 checks for closeness of the two sets of coordinate points. Block 161 uses the two sets and redraws the plot enlarged on that window. Block 162 is transferred to when the user has not moved the cursor 20 for the second set of coordinate points, implying that direct input of window coordinate points is being requested. Block 162 performs this request. Block 163 computes minimum and maximum values and transfers to replot the data with the newly specified minimum and maximum. 
     Referring now to FIG. 3L, the DRAWIT subroutine is shown. In block 164 the shading storage, a bit map representation of the entire screen 14 is set to zero i.e., no shade. Block 165 determines the line type, curve or linear, and block 166 plots the symbols, if required. Block 167 determines the line mode, solid or dashed. Block 168 begins to plot the curve, determining if symbols at each coordinate point are required, and block 169 instructs the plotting of the symbols. Via block 170, if the curve type is linear, then a straight line is drawn between data points. Data interpolation using the Hiroshi Akima technique is executed via block 172, using all the points on the given line and generating short line segments. Block 173 determines the type of line, i.e., dashed, solid or shaded. Block 174 plots the line as dashed using one of several different pre-programmed dash sequences. Block 175 imposes the shading on the plot using the following algorithm: in block 164, a bit map representation of the plot is initialized (about 20,000 points per plot); as the curve in which shading was requested is drawn, the points in the columns beneath the curve are examined; if a point (single bit) is not already shaded (bit is zero), then it is set to shade (bit set to 1); conversely if the bit is set to shade (bit equals 1), then it is reset to no shade (bit equals 0). This algorithm permits any shape defined by a curve, open or closed to be shaded. Further related discussion is found hereinafter regarding the subroutine SHADE. Block 176 determines if the wide solid line is required and block 177 plots the wide curve by performing a &#34;hem stitch&#34; motion as the curve is drawn. Block 178 simply draws the regular line, single width. Block 179 checks to see if any more lines are to be drawn, and if not returns control to block 77 in FIG. 3B. 
     Referring now to FIG. 3M, the PTITLE subroutine (plot titles) is shown. Block 180 gets the size of the title as inputted or changed by the user. Block 181 uses the two slope points also inputted by the user to compute the title angle. Block 183 eliminates all leading blanks from the label. Block 183 begins scanning the title for three consecutive blanks used as a signal to terminate this line and begin a new line. Block 184 does the termination. Likewise, if the scan does not find three consecutive blanks, then the entire title is assumed on one line. Block 186 checks user input to see if title is centered or left shifted. Block 189 plots the title and increment to the next line. Block 190 checks the length of the line and stores the maximum line length. Block 192 checks for more title lines in the same title and transfers when finished to block 193. Block 193 stores the maximum line length and computes four coordinates around the title and stores these for later use. FIG. 3N shows the flow for the grid drawing subroutine PGRIDY/PGRIDX. Block 194 determines which grid lines are to be drawn. Block 195 moves into position to begin the grid line on either axis. Block 196 computes all possible intersections of this line with all title boundaries as determined in the PTITLE routine of FIG. 3M. False crossings are eliminated and the sequence of real crossings is stored in the order of crossing. Block 197 initializes the position and counter while block 198 determines if the end of the current grid line is reached. Block 203 checks for more grid lines if the current end is reached. Block 199 computes the next intersection of the grid line with the next title boundary it crosses and block 200 checks to see if drawing from the current position to intersection is crossing a title block. If it is, then block 201 skips drawing and moves to the computed intersection. Block 202 is used to draw a line to the intersection when a line is not passing thru title. This process is repeated looping back thru to block 198 until the end of the current grid line is reached. 
     Referring now to FIG. 3O, the SHADE subroutine is described. Block 204 checks for the first point of a line segment and block 205 stores it. In succeeding passes thru SHADE control is transferred to block 206. Block 206 takes two points and examines all columns of points between the X-axis and the line spanning the interval of the points. Within each column beneath this interval each possible shade point is checked. If the point is already shaded, it is unshaded and similarly, a point unshaded is shaded. This process is repeated until the line is traversed to its end. Also in FIG. 3O, the AXIS subroutine is shown. Block 211 uses the minimum and maximum values determined from the coordinate data and generates sealing in a multiple of 1, 2 or 5 units. Tick marks and numbers required on axis are computed and plotted. 
     Referring now to FIG. 3P, subroutine SHADEIT is shown. SHADEIT actually plots the points assembled with the SHADE subroutine shown in FIG. 3O. The exception is that points within a title block are omitted from shading. Block 212 sets the column row position and begins checking all 20,000 possible points. Block 213 checks point for shade. If point is shaded block 214 checks to see if shaded point is within label. If not, block 215 plots the point and block 216 increments the row counter. Block 217 checks for more rows and block 218 resets to Row 1 and moves to the next column. Block 219 then checks for more columns, and if none are found, return to block 85. 
     Therefore, it is apparent that the present invention provides an improved process implemented by a computer for generating graphical artwork of a finished quality ready for photolithographic reproduction. More particularly, the present invention provides a computer-aided process for producing original camera-ready plots in full detail without requiring any manual drafting. Furthermore, the disclosed invention provides an automated process for creating revised camera-ready graphical plots that permits custom editing and correcting of existing plots quickly and precisely without manually redrawing revisions and affixing them to existing plots. In addition, the disclosed computer-aided process for graphical artwork generation is cost effective, reliable in performance, easily adapted to existing automated graphic art equipment. 
     Obviously, other embodiments and modifications of the present invention will readily come to those of ordinary skill in the art having the benefit of the teachings presented in the foregoing description and drawings. It is therefore to be understood that various changes in the details, materials, steps, and arrangement of parts, which have been described and illustrated to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. ##SPC1## ##SPC2## ##SPC3## ##SPC4## ##SPC5## ##SPC6##