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<<LINEAR|LOGARITHMIC>
<FROM x y z> <TO x y z> <SIZE value>
<MINIMUM value> <STEP value> <MAXIMUM value>
<MODE value>
<TEXT-PLANE-NORMAL x y z>
<TICK value>
<TITLE "string">>
Default: AXIS ABSOLUTE LINEAR -
FROM 0,0,0 TO 1,0,0 SIZE 1 -
MINIMUM 0 STEP 0.1 MAXIMUM 1 -
MODE -1 TEXT-PLANE-NORMAL 0,0,-1 TICK +0.015 TITLE ''
Draw an optionally labelled and numbered coordinate axis. Coordinates
may be either ABSOLUTE, or RELATIVE to the current point, as determined
by the first subcommand. Relative coordinates are particularly useful
for defining position-independent axes. In either case, the current
point on successful command completion is at the axis origin at the
FROM point.
Parameters may be specified in any order, and if any occur more than
once, the last one specified is used. The FROM subcommand specifies
the axis origin. The TO subcommand specifies the direction of the
axis, and if the SIZE subcommand is NOT given, the end point of the
axis. An explicit SIZE command overrides the default axis length,
which is the distance between the FROM and TO points.
The axis numbering is specified by the MINIMUM, MAXIMUM, and STEP
parameters. For a linear axis, the numbering will start at the MINIMUM
value, end at the MAXIMUM value, and have tick marks and numbering
every STEP value, or some nice multiple thereof if the stepsize is so
small that numbering would overlap. For a logarithmic axis, STEP
specifies the length of one decade on the axis, and MAXIMUM is then
ignored. For example, with subcommands MINIMUM 100 STEP 3 SIZE 10,
there would be 3 complete decades on the axis: 10**2, 10**3, 10**4,
followed by a partial decade. Alternatively, if STEP is not specified,
MAXIMUM specifies the ending value on the axis, and the number of
decades will then be log10(MAXIMUM/MINIMUM).
The MODE parameter encodes option flags stored in the low-order bits of
the integer value. These are selected by adding one or more of the
following option values, and then setting the sign of the resulting sum
to select numbering and titling above (+) or below (-) the axis.
1 - Number the axis. Even values of MODE suppress numbering, but
still affect the choice of tick mark spacing.
2 - Numbering perpendicular (i.e. rotated -90 degrees) to the axis;
otherwise it is parallel to the axis.
4 - Omit the first number along the axis. This can be useful to
prevent text overlap when more than one axis is drawn from a
point.
8 - Omit the last number along the axis.
16 - Omit any zero number along the axis. This can be useful for
drawing axes intersecting at the origin.
Any value outside the legal range -31..+31 will raise an error
condition. The usual choice for a numbered left vertical (Y) axis will
be MODE = +3, and for a numbered lower horizontal (X) axis will be MODE
= -1. The usual choice for an unnumbered right vertical axis will be
MODE = +2 or -2, and for an unnumbered upper horizontal axis will be
MODE = 0.
The sizes and positions of number labels, even if they are not drawn,
affect the choice of where longer tick marks are drawn. In the common
case where the four sides of a graph have axes, but two are unnumbered,
for the unnumbered axes, simply subtract 1 from the unsigned MODE value
used for the opposite numbered axis.
The TICK subcommand specifies the size (in world units) and direction
(+ is above, - is below) of tick marks perpendicular to the axis.
Making this value equal to the length of the perpendicular axis causes
grid lines to be drawn over the entire frame.
The TITLE subcommand defines an axis title, which may be a null string;
it will be drawn unless MODE 0 is specified.
For a 3-D axis, it is necessary to define the plane in which text
annotating the axis is to be drawn. The TEXT-PLANE-NORMAL defines a
vector normal to the text plane and pointing away from the viewer. The
default normal 0,0,-1 points into the XY plane along the -Z axis, which
is appropriate for a 2-D axis.