6.2 Axis Systems

This section describes  subroutines  that allow the user  to
modify axis systems.  The position  of an  axis system,  the
size,  the scaling,  ticks,  labels  and axis titles  can be
altered in  any way.  Some of the routines defining axis at-
tributes can also be used with secondary axes. Routines that
set axis attributes can be used  for one or for any combina-
tion of axes.  The axes are identified by a character string
that can contain the characters 'X', 'Y' and 'Z' in any com-
bination.

6.2.1 Modifying the Type

                         A X S T Y P

The routine AXSTYP defines the type of an axis system.  Axis
systems  can be plotted  as rectangles or in a crossed form.
For crossed axis systems, the scaling must be linear and the
axis limits must contain the origin.

The call is:  CALL AXSTYP (COPT)                     level 1

COPT          is a character string defining the type.
 = 'RECT'     defines a rectangular axis system. 
 = 'CROSS'    defines a crossed axis system.
                                     Default: COPT = 'RECT'.

6.2.2 Modifying the Position and Size

                         A X S P O S

AXSPOS determines the position of an axis system.

The call is:  CALL AXSPOS (NXA, NYA)                 level 1

NXA, NYA      are  plot  coordinates  that  define the lower
              left  corner of  an axis  system.  By default,
              axis systems  are  centred in  the X-direction
              while  NYA  is set to the value (page height -
              300).

                         A X S O R G

AXSORG is an alternate routine for defining the position  of
a crossed axis system.

The call is:  CALL AXSORG (NX, NY)                   level 1

NX, NY        are plot coordinates  that define the position
              of the origin of a crossed axis system.

                         A X S L E N

AXSLEN defines the size of an axis system.

The call is:  CALL AXSLEN (NXL, NYL)                 level 1

NXL, NYL      are the length and height of an axis system in
              plot coordinates.  The default values  are set
              to 2/3 of the page length and height.

                         C E N T E R

A call to the routine CENTER will centre  the axis system on
the page.  All elements of an axis system, including titles,
axis labels and names, will be taken into consideration. The
centralisation is done by GRAF through changing the position
of the origin. Therefore, all plotting routines called after
GRAF will work with the new origin.

The call is:  CALL CENTER                      level 1, 2, 3

Notes:     -  If there are several axis systems on the page,
              the origin  will be changed  only by the first
              call to GRAF.
           -  The character height of titles  should  be de-
              fined with HTITLE if it is different  from the
              current  character height in GRAF.

6.2.3 Axis Scaling

                         S C A L E

This routine sets the axis scaling to logarithmic or linear.

The call is:  CALL SCALE (CSCL, CAX)           level 1, 2, 3

CSCL = 'LIN'  denotes linear scaling.
     = 'LOG'  denotes logarithmic scaling.
CAX           is a character string that defines the axes.
                                     efault: ('LIN', 'XYZ').

Note:         For logarithmic scaling, the corresponding pa-
              rameters in GRAF must be exponents of base 10.

                         S E T S C L

The parameters in  GRAF  will be calculated automatically by
DISLIN  if the routine  SETSCL  is used.  In this case, GRAF
must have dummy parameters in which  DISLIN returns the cal-
culated values.

The call is:  CALL SETSCL (XRAY, N, CAX)       level 1, 2, 3

XRAY          is a vector  that  contains  user coordinates.
              SETSCL calculates the minimum and maximum  va-
              lues  of the data and  stores them in a common
              block.
N             is the number of points in XRAY.
CAX           is a character string that defines the axes.

Notes:     -  SETSCL can be used with linear and logarithmic
              scaling and with all label types.
           -  The calculation of scaling and label values is
              done by  GRAF.  The minimum and maximum of the
              data are  always used for the lower and  upper
              limits of an axis while even values are calcu-
              lated for the labels.
           -  The number of  digits after the decimal  point
              will be set automatically.
           -  If the scaling of an axis is logarithmic,  la-
              bels will be plotted with the format 'LOG'.

6.2.4 Modifying Ticks

                         T I C K S

This routine is used to define  the number  of ticks between
axis labels.

The call is:  CALL TICKS (NTIC, CAX)           level 1, 2, 3

NTIC          is the number of ticks (>= 0).
CAX           is a character string that defines the axes.
                                        Default: (2, 'XYZ').

                         T I C P O S

This routine defines the position of ticks.

The call is:  CALL TICPOS (CPOS, CAX)          level 1, 2, 3

CPOS          is a character string defining the position.
  = 'LABELS'  means that  ticks will  be plotted on the same
              side as labels.
  = 'REVERS'  means that ticks  will be plotted inside of an
              axis system.
  = 'CENTER'  means that ticks  will be centred  on the axis
              line.
CAX           is a character string that defines the axes.
                                 Default: ('LABELS', 'XYZ').

                         T I C L E N

TICLEN sets the lengths of major and minor ticks.

The call is:  CALL TICLEN (NMAJ, NMIN)         level 1, 2, 3

NMAJ          is the length  of major  ticks in plot coordi-
              nates (> 0).
NMIN          is the length  of minor  ticks in plot coordi-
              nates (> 0).
                                          Default: (24, 16).

                         T I C M O D

The routine TICMOD modifies the plotting of minor tick marks
on calendar axes.  By default,  a major tick  is  plotted at
each date label and no minor ticks are plotted.

The call is:  CALL TICMOD (COPT, CAX)          level 1, 2, 3

COPT          is a character string defining the tick marks.
  = 'NONE'    means that no minor ticks will be plotted.
  = 'DAYS'    means that ticks will be plotted for every
              day.
  = 'MONTH'   means that ticks will be plotted for every
              month.
  = 'DMONTH'  means that ticks will be plotted for every 
              second month.
  = 'QUARTER' means that ticks will be plotted on the first
              of January, April, July and October.
  = 'HALF'    means that ticks will be plotted on the first
              of January and July.
  = 'YEAR'    means that ticks will be plotted for every
              year.
CAX           is a character string that defines the axes.
                                   Default: ('NONE', 'XYZ').

                         L O G T I C

The  appearance of minor ticks  on logarithmic axes  differs
slightly from  linear axes.  By default,  logarithmic  minor
ticks  are generated automatically if the label step is 1 or
-1 and if the number of ticks in TICKS is greater than 1. If
the step has another value, minor ticks are plotted  as spe-
cified in TICKS. This algorithm can be modified with LOGTIC.

The call is:  CALL LOGTIC (CMOD)               level 1, 2, 3

CMOD          is a character string defining the  appearance
              of logarithmic ticks.
   = 'AUTO'   defines default ticks.
   = 'FULL'   means that logarithmic minor ticks will be ge-
              nerated for every cycle even if the label step
              is not 1 but some other integer.
                                     Default: CMOD = 'AUTO'.

6.2.5 Modifying Labels

                         L A B E L S

LABELS  determines  which label types  will be plotted on an
axis.

The call is:  CALL LABELS (CLAB, CAX)          level 1, 2, 3

CLAB          is a character string that defines the labels.
  = 'NONE'    will suppress all axis labels.
  = 'FLOAT'   will plot labels in floating-point format.
  = 'EXP'     will plot floating-point labels in exponential
              format where fractions range between 1 and 10.
  = 'FEXP'    will plot  labels in the format  fEn  where  f
              ranges between 1 and 10.
  = 'LOG'     will plot logarithmic labels  with base 10 and
              the corresponding exponents.
  = 'CLOG'    is similar to 'LOG' except that the entire la-
              bel is  centred  below  the  tick  mark;  with
              'LOG', only the base '10' is centred.
  = 'ELOG'    will plot  only the  logarithmic values of la-
              bels.
  = 'TIME'    will plot time labels in the format 'hhmm'.
  = 'HOURS'   will plot time labels in the format 'hh'.
  = 'SECONDS' will plot time labels in the format 'hhmmss'.
  = 'DATE'    defines date labels.
  = 'MAP'     defines geographical  labels which are plotted
              as non  negative  floating-point  numbers with
              the  following characters  'W',  'E',  'N' and
              'S'.
  = 'LMAP'    is simular to 'MAP' except that lowercase cha-
              racters are used.
  = 'DMAP'    selects labels  that are plotted as  floating-
              point numbers with degree symbols.
  = 'MYLAB'   selects labels that are defined  with the rou-
              tine MYLAB. 
CAX           is a character string that defines the axes.
                                  Default: ('FLOAT', 'XYZ').

Notes:     -  The values 'LOG', 'CLOG' and 'ELOG' can be on-
              ly used with logarithmic scaling. If these la-
              bel types are used with linear scaling, DISLIN
              will change them   to 'FLOAT'.
           -  For the values  'TIME', 'HOURS' and 'SECONDS',
              the corresponding parameters in  GRAF  must be
              in seconds since midnight.
           -  For the value 'DATE',  the corresponding para-
              meters in GRAF must be  in days  since  a base
              date.  The base date  can be  defined with the
              routine BASDAT while the  number of days since
              the base date can be  calculated with the rou-
              tine INCDAT. Date labels can be modified  with
              the routine LABMOD.

                         M Y L A B

MYLAB defines user labels.

The call is:  CALL MYLAB (CSTR, ITICK, CAX)    level 1, 2, 3

CSTR          is a character string containing  a label  (<=
              32 characters).
ITICK         is the tick number  where the  label  will  be
              plotted (<= 20). Tick numbering starts with 1.
CAX           is a character string that defines the axes.

                         L A B T Y P

LABTYP defines horizontal or vertical labels.

The call is:  CALL LABTYP (CTYPE, CAX)         level 1, 2, 3

CTYPE         is a character string defining the direction.
   = 'HORI'   defines horizontal labels.
   = 'VERT'   defines vertical labels.
CAX           is a character string that defines the axes.
                                   Default: ('HORI', 'XYZ').

                         L A B P O S

LABPOS defines the position of labels.

The call is:  CALL LABPOS (CPOS, CAX)          level 1, 2, 3

CPOS          is a character string defining the position.
  = 'TICKS'   means  that  labels  will be  plotted at major
              ticks.
  = 'CENTER'  means  that labels will be centred between ma-
              jor ticks.
  = 'SHIFT'   means that the starting and end labels will be
              shifted.
CAX           is a character string that defines the axes.
                                  Default: ('TICKS', 'XYZ').

                         L A B J U S

LABJUS defines the alignment of axis labels.

The call is:  CALL LABJUS (CJUS, CAX)          level 1, 2, 3

CJUS          is a character string  defining  the alignment
              of labels.
  = 'AUTO'    means that labels are automatically justified.
  = 'LEFT'    means that labels are left-justified.
  = 'RIGHT'   means that labels are right-justified.
  = 'OUTW'    means that labels are  left-justified  on  the
              left and lower axes of an axis system.  On the
              right and upper axes,  labels are right-justi-
              fied.
  = 'INWA'    means that labels are  right-justified  on the
              left and  lower axes of an axis system. On the
              right and upper axes,  labels are  left-justi-
              fied.
CAX           is a character string that defines the axes.
                                   Default: ('AUTO', 'XYZ').

                         D I G I T S

This routine  sets the number  of digits  after the  decimal
point displayed in labels.

The call is:  CALL DIGITS (NDIG, CAX)          level 1, 2, 3

NDIG  = -1  defines integer labels.
      =  0  defines integer labels  followed  by  a  decimal
            point.
      =  n  defines the number  of digits  after the decimal
            point. The last digit will be rounded up.
CAX         is a character string that defines the axes.
                                        Default: (1, 'XYZ').

                         I N T A X

With the routine INTAX,  all axes will be labeled with inte-
gers.

The call is:  CALL INTAX                       level 1, 2, 3

                         L A B D I S

This routine sets the distance between labels and ticks.

The call is:  CALL LABDIS (NDIS, CAX)          level 1, 2, 3

NDIS          is the distance in plot coordinates.
CAX           is a character string that defines the axes.
                                       Default: (24, 'XYZ').

                         L A B M O D

The routine  LABMOD  modifies the appearance  of date labels
enabled with the keyword 'DATE' in the routine LABELS.  Nor-
mally, date labels will be plotted in the form dd-mmm-yyyy.

The call is:  CALL LABMOD (CKEY, CVAL, CAX)    level 1, 2, 3

CKEY          is a  character string  containing  one of the 
              following keywords:

 = 'YEAR'     means that the century field will be  modified
              in date labels.  For CKEY = 'YEAR',  CVAL  can 
              have the values 'NONE', 'SHORT' and 'FULL'. 
              'NONE' suppresses the year field while 'SHORT'
              suppresses the century in the year field.  The
              default value is 'FULL'. 

 = 'DAYS'     means that the day field will be modified. 
              CVAL  can  have  the values  'NONE',  'SHORT', 
              'LONG', 'NAME' and 'FULL'.  For CVAL = 'NONE',
              the day field  will be suppressed,  for CVAL =
              'SHORT',  the day will be plotted  as a number
              without a  leading zero.  CVAL = 'LONG'  means
              that the day will be plotted as a  number with
              two digits, CVAL = 'NAME' means that abbrevia-
              tions of the weekday names will be plotted and
              CVAL = 'FULL'  means  that  the  full  weekday
              names will be displayed.  The default value is
              CVAL = 'LONG'.

 = 'MONTH'    means  that the  month field will be modified.
              CVAL  can  have the  values  'NONE',  'SHORT',
              'LONG', 'NAME', 'TINY' and 'FULL'.  
              For  CVAL = 'NONE',  the month  field  will be
              suppressed, for CVAL = 'SHORT', the month will
              be plotted as a number without a leading zero.
              CVAL = 'LONG'  means that the  month  will  be
              plotted as a  number with two digits,   CVAL = 
              'NAME' means that abbreviations  of  the month
              names will  be plotted,  CVAL =  'TINY'  means
              that only the first  character of  month names
              will be plotted and  CVAL = 'FULL' means  that
              the full  month names will  be displayed.  The
              default value is CVAL = 'NAME'.

 = 'LANG'     defines  the  language  used  for weekdays and
              month names in date labels.  CVAL can have the
              values 'ENGLISH' and 'GERMAN'. The default va-
              lue for CVAL is 'ENGLISH'.
   
 = 'FORM'     defines the order of the date fields. CVAL can
              have the values 'DMY',  'DYM',  'YDM',  'YMD',
              'DYM' and 'MDY'. The default is CVAL = 'DMY'.
  
 = 'SEPA'     defines a separator character used in date la-
              bels.  CVAL is a  character string  containing
              the separator character. The default is 
              CVAL = '-'.
   
 = 'CASE'     defines  if weekdays and month names are plot-
              ted in  uppercase characters  or in  lowercase
              characters with a leading uppercase character.
              CVAL can have the values  'UPPER' and  'NONE'.
              The default value is 'NONE'.
  
 = 'STEP'     defines a step between labels.  CVAL can  have
              the values  'DAYS',  'MONTH', 'DMONTH', 'QUAR-
              TER',  'HALF'  and  'YEAR'. For CVAL = 'DAYS', 
              the label step specified  in the routine  GRAF
              will be used.  The  default  value  is  CVAL = 
              'DAYS'.
  
CAX           is a character string that defines the axes.

                         P O L M O D

The routine  POLMOD  modifies the appearance of angle labels
plotted with the routine POLAR.

The call is:  CALL POLMOD (CPOS, CDIR)         level 1, 2, 3

CPOS          is a character string that defines the positi-
              on of the first label.  CPOS can have the val-
              ues 'RIGHT', 'TOP', 'LEFT' and 'BOTTOM'.
CDIR          defines the direction of the labels.  CDIR can
              have the values 'CLOCKWISE' and 'ANTICLOCK'.
                            Default: ('RIGHT', 'ANTICLOCK').

                         T I M O P T

With  TIMOPT  time  labels  can  be  plotted  in the  format
'hh:mm'. The default is 'hhmm'.

The call is:  CALL TIMOPT                      level 1, 2, 3

                         R G T L A B

The routine RGTLAB right-justifies user labels.  By default,
user labels are left-justified.

The call is: CALL RGTLAB                       level 1, 2, 3

6.2.6 Modifying Axis Titles

                           N A M E

NAME defines axis titles.

The call is:  CALL NAME (CSTR, CAX)            level 1, 2, 3

CSTR          is a character string containing the axis tit-
              le  (<= 132 characters).
CAX           is a character string that defines the axes.
                                      Default: (' ', 'XYZ').

                         H N A M E

HNAME defines the character height for axis names.

The call is:  CALL HNAME (NHNAME)              level 1, 2, 3

NHNAME        is the character height in plot coordinates.
                                        Default: NHNAME = 36

                         N A M D I S

NAMDIS sets the distance between axis names and labels.

The call is:  CALL NAMDIS (NDIS, CAX)          level 1, 2, 3

NDIS          is the distance in plot coordinates.
CAX           is a character string that defines the axes.
                                       Default: (30, 'XYZ').

                         N A M J U S

The routine NAMJUS defines the alignment of axis titles.

The call is:  CALL NAMJUS (CJUS, CAX)          level 1, 2, 3

CJUS          is a character string that can have the values
              'CENT', 'LEFT' and 'RIGHT'.
CAX           is a character string that defines the axes.
                                   Default: ('CENT', 'XYZ').

                         R V Y N A M

The routine RVYNAM is used to plot names on right Y-axes and
colour bars at an angle of 90 degrees.  By default, they are
plotted at an angle of 270 degrees.

The call is:  CALL RVYNAM                      level 1, 2, 3

6.2.7 Suppressing Axis Parts

                         N O L I N E

After a call to  NOLINE  the plotting  of axis lines will be
suppressed.

The call is: CALL NOLINE (CAX)                 level 1, 2, 3

CAX          is a character string that defines the axes.

                         A X E N D S

With a call to AXENDS certain labels can be suppressed.

The call is:  CALL AXENDS (COPT, CAX)          level 1, 2, 3

COPT          is a character string  that defines  which la-
              bels will be suppressed.
  = 'NONE'    means that all labels will be displayed.
  = 'FIRST'   means  that only  the starting label  will  be
              plotted.
  = 'NOFIRST' means  that the  starting  label  will  not be
              plotted.
  = 'LAST'    means that only the ending label will be plot-
              ted.
  = 'NOLAST'  means that the ending label  will not be plot-
              ted.
  = 'ENDS'    means that only  the start and end labels will
              be plotted.
  = 'NOENDS'  means that start  and end labels  will be sup-
              pressed.
CAX           is a character string that defines the axes.
                                   Default: ('NONE', 'XYZ').

                         N O G R A F

The routine  NOGRAF  suppresses the plotting of an axis sys-
tem.

The call is:  CALL NOGRAF                            level 1

                         A X 2 G R F

The routine  AX2GRF  suppresses the plotting of the upper X-
and left Y-axis.

The call is:  CALL AX2GRF                      level 1, 2, 3

                         S E T G R F

SETGRF removes a part of an axis  or a complete axis from an
axis system.

The call is:  CALL SETGRF (C1, C2, C3, C4)     level 1, 2, 3

Ci            are  character  strings  corresponding  to the
              four axes of an axis system. C1 corresponds to
              the lower X-axis, C2 to the left Y-axis, C3 to
              the upper X-axis  and C4 to the right  Y-axis.
              The parameters  can have  the  values  'NONE',
              'LINE', 'TICKS',  'LABELS'  and  'NAME'.  With
              'NONE', complete axes will be suppressed, with
              'LINE', only axis lines will be plotted,  with
              'TICKS', axis lines and ticks will be plotted,
              with  'LABELS',  axis lines,  ticks and labels
              will be plotted and with 'NAME', all axis ele-
              ments will be displayed.
                Default: ('NAME', 'NAME', 'TICKS', 'TICKS').

Notes:     -  By default,  GRAF plots a frame of thickness 1
              around axis systems. Therefore, in addition to
              the parameter 'NONE',  FRAME  should be called
              with the parameter 0 for suppressing  complete
              axes.
           -  SETGRF  does not  reset  the effect of  NOGRAF
              and NOLINE. This must be done using RESET.

6.2.8 Modifying Clipping

                         C L P W I N

The routine  CLPWIN  defines a rectangular  clipping area on
the page.

The call is:  CALL CLPWIN (NX, NY, NW, NH)     level 1, 2, 3

NX, NY        are the  plot  coordinates  of the  upper left
              corner.
NW, NH        are the width  and height  of the rectangle in
              plot coordinates.

                         C L P B O R

The routine CLPBOR sets the clipping area to the entire page
or to the axis system.

The call is:  CALL CLPBOR (COPT)               level 1, 2, 3

COPT          is a character string that can have the values
              'PAGE' and 'AXIS'.
                                     Default: COPT = 'PAGE'.

                         N O C L I P

The suppressing of lines  outside  of the borders of an axis
system can be disabled with NOCLIP.

The call is:  CALL NOCLIP                      level 1, 2, 3

                         G R A C E

GRACE defines a margin around axis systems  where lines will
be clipped.

The call is:  CALL GRACE (NGRA)                level 1, 2, 3

NGRA          is the  width  of the  margin  in plot coordi-
              nates.  If NGRA is  negative,  lines  will  be
              clipped inside the axis system.
                                          Default: NGRA = -1

6.2.9 Framing Axis Systems

                         F R A M E

FRAME defines  the thickness  of frames plotted  by routines
such as GRAF and LEGEND.

The call is:  CALL FRAME (NFRM)                level 1, 2, 3

NFRM          is the thickness  of the frame in plot coordi-
              nates. If NFRM is negative,  the frame will be
              thickened  from the inside.  If positive,  the
              frame will be thickened towards the outside.
                                           Default: NFRM = 1

                         F R M C L R

The colour of frames can be defined with the routine FRMCLR.

The call is:  CALL FRMCLR (NCLR)               level 1, 2, 3

NCLR          is a colour number between -1 and 255. 
              If NCLR = -1, the current colour is used.
                                          Default: NCLR = -1

6.2.10 Setting Colours

                         A X S B G D

The routine AXSBGD defines a background colour for axis sys-
tems.

The call is:  CALL AXSBGD (NCLR)               level 1, 2, 3

NCLR          is a  colour  number  between  -1  and 255. If
              NCLR = -1, the background of an axis system is
              not filled in GRAF.
                                          Default: NCLR = -1

                         A X C L R S

AXCLRS selects colours for single parts of axes.

The call is:  CALL AXCLRS (NCLR, COPT, CAX)    level 1, 2, 3

NCLR          is a  colour  number  between  -1  and 255. If
              NCLR = -1, the actual colour is used.
COPT          is a  character string  that can  have the va-
              lues  'LINE',  'TICKS',  'LABELS',  'NAME' and
              'ALL'.
CAX           is a character string that defines the axes.
                                Default: (-1, 'ALL', 'XYZ').

Note:         By default,  a frame of thickness 1 is plotted
              around  axis systems.  This  may  overplot the 
              colour of axis lines (see FRAME, FRMCLR).

6.2.11 Axis System Titles

                         T I T L I N

This subroutine  defines up to four  lines of  text used for
axis system titles. The text can be plotted with TITLE after
a call to GRAF.

The call is:  CALL TITLIN (CSTR, IZ)           level 1, 2, 3

CSTR          is a character string (<= 132 characters).
IZ            is an integer that contains a value between  1
              and 4  or  -1 and -4.  If IZ is negative,  the
              line will be underscored.
                  Default: All lines are filled with blanks.

                         T I T J U S

The routine TITJUS defines the alignment of title lines.

The call is:  CALL TITJUS (CJUS)               level 1, 2, 3

CJUS          is a  character string that can  have the  va-
              lues 'CENT', 'LEFT' and 'RIGHT'.
                                     Default: CJUS = 'CENT'.

                         L F T T I T

Title lines are centred  above axis systems  by default  but
can be left-justified  with a call to  LFTTIT.  This routine
has the same meaning as TITJUS ('LEFT').

The call is:  CALL LFTTIT                      level 1, 2, 3

                         T I T P O S

The routine TITPOS defines the position of title lines which
can be plotted above or below axis systems.

The call is:  CALL TITPOS (CPOS)               level 1, 2, 3

CPOS          is a character string that can have the values
              'ABOVE' and 'BELOW'.
                                    Default: CPOS = 'ABOVE'.

                         L I N E S P

LINESP defines the spacing between title and legend lines.

The call is:  CALL LINESP (XFAC)               level 1, 2, 3

XFAC          The space  between lines is set to XFAC * cha-
              racter height.
                                        Default:  XFAC = 1.5

                         H T I T L E

HTITLE defines  the character height for titles. The charac-
ter height defined by  HEIGHT  will be used if HTITLE is not
called.

The call is:  CALL HTITLE (NHCHAR)             level 1, 2, 3

NHCHAR        is the character height in plot coordinates.

                         V K Y T I T

The space between titles and axis systems can be enlarged or
reduced with VKYTIT.  By default, the space is 2 * character
height.

The call is:  CALL VKYTIT (NV)                 level 1, 2, 3

NV            is an integer that determines the spacing  be-
              tween axis systems and titles.  If NV is nega-
              tive,  the space will be  reduced by  NV  plot
              coordinates. If NV is positive, the space will
              be enlarged by NV plot coordinates.
                                             Default: NV = 0
