Command: zone

Syntax

{<entity> = } zone <offsets> {
    <pcommand>
    ...
}

Description

Create one or more polygon graphic entities forming a buffer zone from a series of center-lines.

Parameters

• <entity>
  An entity or gstructure identifier. The polygon entities will be given this name. This can be an entity array for multiple entity assignment.

• <offsets>
  The buffer offsets defining the buffer zone widths. This can be a single numeric value which will be applied to all center-lines, or an array of values applied to each center-line or vertex in turn. If there are more vertices than there are offsets, the last offset is re-used. Each offset corresponds to half the buffer zone width.

• <pcommand>
  A command line containing either:

1. a language command to be executed normally, which may or may not generate center-line vertices, or

2. a series of point expressions separated by commas defining center-line vertices.

Switches

• -alph=<num>
  An alpha transparency factor between 0 and 1. A value 1 implies fully opaque, 0 means fully transparent (therefore invisible). The default is 1.

• -ap=<num>
  The number of line approximations to be used when calculating zone ends and corners at center-line vertices. If omitted, the default curve approximation value def_approx is used.

• -br=<num>
  A brightness factor between -1 and +1. A value 0 means normal, -1 means very dark (black), +1 means very bright (white). The default is 1.

• -col=<color>
  The color of the polygons. If included, this will override any color defined in the linestyle (-ls) or fillstyle (-fil). If omitted, the value no_change is used.

• -ff
  Fix the fill color of created polygons so that they are unaffected by subsequent modifications to the entity color.

• -fil=<fillstyle>
  The fill characteristics of the polygon interiors. If omitted, the polygons are not filled. Note: <fillstyle> can be a fillstyle, color, tile, hatchstyle or graduation.

• -fr=<num>
  Define a fragment number for the entity. If omitted, the default fragment def_fragment is used.

• -g=<groups>
  The graphic groups of which the entities are to be part.

• -ls=<linestyle> | <color>
  The linestyle of the polygon edges. This can be a linestyle or a color. If omitted, the current modeling color (def_color) is used.

• -pc
  Compute the para-centroid of any created polygon and make it the polygon’s origin.

• -ra=<num>
  Define a rank for the entity. If omitted, the default rank def_rank is used.

• -th=<num>
  The thickness of the polygon edges. If included, this will override any thickness defined in the linestyle (-ls) or hatch style (-fil) if applicable.

• -v
  Apply the zone offsets to the vertices rather than to the center-lines (the default).

Notes

This command creates one or more graphic entities of type polygon.

Donut shapes produced by the buffer zone will be resolved correctly and may produce hole polygons.

Polygons which reduce to a line for one reason or another are ignored.

All polygons created (including holes and islands) by a zone command form the contents of the group these.

During vertex definition, a point phrase beginning with @ will indicate a move of the graphic control position without creating an arm of the buffer zone polygon. Thus disjoint buffer zones can be produced.

The system numeric found records the number of polygons created by the zone command. Holes and islands are excluded from the count.

Examples:

Create a buffer zone from a single line.

zone 50, -ap=32 {
   gc, e:500
}

Create a complex buffer zone (the vertices are defined interactively).

plan
zone 700, -col=green, -fil=yellow {
   pseries; # Command
   r; # Point phrase "return to start"
}

Create a named conic buffer zone.

entity conezone = zone <0,500>,-v {
   gc, pcur
}

See Also