CI - Circle plot - Page 171

2001/10/02 

CHAPTER 4 HP-GL/2 - 23 

• 

The following 

flags

 are used: 

':' -   

Select pen.  The number which follows is the required pen number.  A PE command that does not 
include a select pen command uses the currently selected pen. 

'<' -    Pen up.  The pen is raised and moved to the specified coordinate pair.  All coordinate pair values 

not preceded by this flag are automatically interpreted as pen down plotting commands. 

'>' -    Fractional data.  The value following the flag specifies the number of fractional binary bits in the 

coordinate data. 

'=' -    Absolute plotting mode.  The pair of coordinates which follow this flag are absolute coordinates. 
'7' -    7 bit mode.  All subsequent coordinate values within this PE command are to be interpreted as 7-bit 

values, that is, encoded in base 32.

• 

If you use the ':' 

flag

 in polygon mode it is ignored as the SP command has no effect in this mode.

• 

Values and coordinates are encoded in base 64 or base 32.  Values determine the setting of the immediately 
preceding 

flag

.  Legal values and coordinates are as follows: 

Pen number -   

0 (white) or 1(black) 

Number of fractional binary bits -   

-26 to 26.  The default is 0. 

x- and y -coordinates -   

(-230) to 230 - 1 current units.  If the pen position is moved 
outside this range, subsequent plotting commands are ignored 
until an absolute coordinate pair within the allowable range is 
specified. 

• 

Flag 

and coordinate values are encoded as either base 64 or base 32 numbers and then transmitted as ASCII 

character codes.  Base 64 is the default.  Use Base 64 if your computer can send data without a parity bit.  
Use base 32 if your system requires a parity bit. 

• 

To encode an integer proceed as follows.  If the number is negative,  take the absolute value,  multiply by 
2 and add 1.  Hence -x : = 2x+1.  If the number is positive simply multiply by 2.  Hence x :=2x.  Convert 
the new number into base 64 or base 32 according  to your system and encode each base 64 or base 32 digit 
as the corresponding ASCII character. 

• 

To encode a real number proceed as follows.  Multiply the number of decimal places in your coordinate's 
data by 3.33 and round the result up to the next highest integer (for example round 6.66 up to 7).  This gives 
the number of binary bits needed to represent the number's fractional part - the value that you will supply with 
the '>' flag.  Call this number n.  Now multiply the number you are encoding by 2

n

.  Round this number to 

the nearest integer and then follow the procedure described above for encoding an integer. 

• 

Transmit each number to the printer least significant digits first.  Terminate each number with the most 
significant digit.  This must be specified from a different ASCII range from the preceding digits in the 
number.  In base 64, non-terminating digits are represented by the numbers 63-126 and terminating digits by 
the numbers 191-254.  In base 32, non-terminating digits are represented by the numbers 63-94 and 
terminating digits by the numbers 95-126.  Hence if using a base 32 number whose least significant digit is 
14, and whose most significant digit is 5,  encode 14 as 77 (63+14) and 5 as 100 (95+5). 

Non-terminator 

Terminator 

Base 64 

63-126 

191-254 

Base 32 

63-94 

95-126 

• 

In symbol mode the PE command draws the specified symbol at each specified point. 

• 

In polygon mode the points specified within the PE command are not plotted.  Instead they are stored in the 
polygon buffer and used when a FP (Fill Polygon) or EP (Edge Polygon) command is used. 

• 

The PE command with no parameters simply updates the carriage return point. 

CI - Circle plot 

CI 

r

(, 

qd

)[;] 

r

 ; Radius of circle ( in current units ) 

qd

 ; Chord angle ( in degrees ) 

• 

The command plots a circle with the current position as the centre, with a radius r and chord angle qd. 

• 

After plotting, the cursor returns to the centre of the circle. 

• 

Plotting takes place irrespective of whether the pen is up or down. 

• 

Valid values for r are specified in the current unit. 

• 

Valid values for 

qd

 are clamped real numbers in the range 0.5° to 180°.  The default value is 5°.