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Create Polylines from the Boundaries of Objects

May 20, 2011

You can create a polyline from the boundaries of overlapping objects that form a closed area. A polyline created using the boundary method is a separate object, distinct from the objects used to create it. You can edit it using the same methods used to edit other polylines.

To expedite the boundary selection process in large or complex drawings, you can specify a group of boundary candidates, called a boundary set. You create this set by selecting the objects you want to use define the boundary.

With the Boundary command, you can designate a specific area of a drawing for operations such as hatching and dimensioning. You create a boundary polyline by selecting an area inside a closed loop. The area you select can be bounded by a single closed object or by multiple objects that intersect.

In cases where objects intersect, ZWCAD interprets the boundary as the closed loop closest to the point specifying the area. In the following figure, for example, the area point selected in the rectangle results in a boundary consisting of the closed loop nearest the point selection, as opposed to the closed loop formed by the rectangle itself.

 Selected point (A) Resulting boundary (B)

To make boundaries more specific, you can create a boundary set. A boundary set specifies which objects are considered in determining the boundary path. This can make creating the boundary polyline faster if you are working with a complex drawing.

In the following figure, the circle and triangle are the selected objects. If you select an area anywhere inside the circle or the triangle, the result is a polyline that bounds the shaded area.

 Selected objects (A and B) Point specified in the selected area (C),which results in a new boundary around the shaded area.

To draw a boundary polyline

1.   Choose Draw > Boundary.

2.   Specify the objects that you want made available for the boundary polyline by doing one of the following:

• All objects Select All Visible Entities to have all objects in the drawing considered when creating the boundary polyline.

• Custom selection Define only specific areas to be considered when creating the boundary polyline, which can improve system performance if you are working with a complex drawing. Click Select Boundary Set. In the drawing, select the objects individually or by choosing a selection method from the prompt box, and then press Enter. The Current Selection Set option becomes selected automatically, which indicates that the objects you selected with the Select Boundary Set button will be considered when creating the boundary polyline.

NOTE You can alternate between All Visible Entities and Current Selection Set without having to select objects again using the Select Boundary Set button. The Current Selection Set option uses the last set of objects you selected with the Select Boundary Set button.

1.   Choose an island-detection option.

2.   Click Select Area.

3.   In the drawing, click inside the area whose closed perimeter forms the boundary, not on the polyline itself. If desired, continue clicking inside additional closed perimeters.

4.   To complete the selection, press Enter.

5.   In the Boundary dialog box, click OK.

Command line BOUNDARY

Commands Reference

3DPOLY: Creates a polyline of line segments in 3D space

BOUNDARY: Creates a region or a polyline from an enclosed area

OFFSET: Creates concentric circles, parallel lines, and parallel curves

PEDIT: Edits polylines and three-dimensional polygon meshes

PLINE: Creates two-dimensional polylines

System Variables Reference

FILLMODE: Specifies whether hatches (including solid-fill), two-dimensional solids, wide polylines, are filled in

HPBOUND: Controls the object type created by the BHATCH and BOUNDARY commands

PLINEGEN: Sets how linetype patterns generate around the vertices of a 2D polyline

PLINETYPE: Specifies whether optimized 2D polylines are used

PLINEWID: Stores the default polyline width

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