HP2XX, A HP-GL Converter
3.1 The coordinate range
The natural unit of length in HP-GL is 1/40 mm = 0.025 mm, so a typical
A4 page covers roughly 11000 x 7500 natural units. Typically, coordinates in
HP-GL commands will be found in the range 0 ... 12000. hp2xx will tell
you the maximum and minimum coordinates ("picture limits")
it finds in your HP-GL picture for both x and y direction.
These values usually roughly cover this range.
Even if your HP-GL source plots in user-specific coordinates (realized
via HP-GL command `SC;' (SCale) ), this remains true, since
hp2xx internally transforms all points back to natural coordinates.
Whenever the above range is grossly violated, you may suspect corrupted
data, because no real plotter would be able to plot such a file.
If you ever discover a picture limit equalling plus or minus 10^10,
your HP-GL probably didn't draw anything. Initially, hp2xx's internal
picture limits are set to impossibly large (or small) values, i. e., +- 10^10,
but the first plot command will set them to values found therein, and successive
plots push the limits outward. Example: xmax starts at -10^10,
the first plot command may change it to 2536, the next to 3470, the next
20 command fall short, etc. Eventually, xmax assumes the largest
value and stays there. Knowledge about these details may sometimes
be crucial (see section 3.3 Scaling to true size).
hp2xx uses the picture limits internally for scaling and fitting the
data into the supplied limiting rectangle (see section 2.2 Sizing your output).
You can also affect the picture limits yourself for special effects
(see section 3.2 Fixed scaling).
