DCL:GRPH1:SCPACK: 3-D User Interface
This is a group of subroutines for polyline primitives.
When the internal variable 'LMISS' handled by glpget/glpset
is set to .true., missing-value handling is performed. In other
words, a polyline is not connected before and after a missing value.
In contrast to 2-D polylines, only solid lines can be used for 3-D polylines,
and they cannot be labeled.