Command: ebuffer

Syntax

{<entity> = } ebuffer <offset>,<elist>

Description

Create one or more polygon graphic entities formed from buffer zones around one or more entities. Effectively "enlarging" the entities, creating new ones.

Parameters

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

• <offset>
  The buffer offset defining the buffer zone width. This is a single numeric value which will be applied to all entity edges to create the buffer.

• <elist>
  A group/entity list defining the source entities are to be processed.

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 created 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 created 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 created polygons. If omitted, the default fragment def_fragment is used.

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

• -h
  Without this switch all polygons with holes are assumed to be valid and are not checked for consistency. Add this switch to resolve polygon/hole anomalies with suspected overlapping edges. The hole polygons will be merged using the boolean difference operator.

• -ls=<linestyle> | <color>
  The linestyle of created 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 created polygons. If omitted, the default rank def_rank is used.

• -sub
  Create any resulting polygons which are islands within holes as sub-polygons of the holes. This is the default behavior. To create islands within holes as top-level polygons use -no_sub.

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

Notes

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

A positive offset will enlarge the entities. A negative offset will reduce the entities. A zero offset is not permitted. The resulting polygon configuration may cause some holes or islands to disappear. Any donut shapes produced by the buffer operation will produce hole polygons. Polygons which reduce to a line for one reason or another are ignored.

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

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

Examples:

Create a buffer zone polygon from a disjoint polyline. Fill it with a blue color.

entity PL2 = lines { (150,0),e:100,n:40,@n:20,n:40,w:100&s:30,r }
ebuffer 5,PL2,-ap=32,-fil=blue

Create a buffer zone polygon around a polygon with a hole.

# Create the outer polygon
  entity poly1 = polygon -fil=red {
   p0, e:120, n:100&w:20, w:20, n:20, w:80, r
}
# Add a hole to it
entity hpoly1 = polygon -par=poly1 {
   (10,10),e:80,n:40,w:40,n:40,w:40,r
}
# Create the buffer polygon
ebuffer 5,poly1,-ap=32

See Also