Autodesk 00128-051462-9310 User Guide - Page 2209

Blocks and Block Libraries Libraries of block content for detail components should be created and stored according to the following guidelines, each of which is discussed in more detail subsequently. ■ Block content should be drawn with the current style of geometry. (See "Using Optimal Geometry" on page 2169.) ■ Blocks should have namespace prefixes. (See "Naming Blocks" on page 2170.) ■ Base points for inserting blocks should be positioned logically. (See "Base Points for Blocks" on page 2170.) ■ Similar blocks should be stored in the same DWG file. (See "Collecting Similar Blocks" on page 2170.) ■ Properties of block entities should be set to ByBlock. (See "Block Properties" on page 2170.) ■ All unnecessary objects should be removed from block library drawings. (See "Removing Unnecessary Objects" on page 2171.) Using Optimal Geometry Many block libraries that were created in legacy versions of AutoCAD contain geometry that is non-optimal in that it can result in performance problems, incorrect snap points, or tolerance discrepancies that cause errors when Aec Modify tools or other AutoCAD editing commands are used. You should avoid using this old-style geometry when creating new blocks, and you should remove or replace it whenever you encounter it in existing block content. The following sections describe five main areas in which you should strive to use optimal geometry. Polylines Prior to AutoCAD Release 14, the polyline entity consisted of multiple vertex entities and was not stored in a compact form. You can identify these old-style polylines by running the LIST command, which identifies them as type POLYLINE. Any such entities should be recreated as new-style polylines by tracing over them manually with the Polyline tool. The LIST command identifies new-style polylines as LWPOLYLINE. Hatch Patterns Be sure to use actual hatch entities when creating blocks that require hatch patterns. Prior to AutoCAD Release 14, hatches were anonymous blocks with all of the entities comprising the pattern stored in the drawing. If you run the LIST command on an entity that appears to be a hatch, and the entity is identified as a BLOCK REFERENCE and has a name beginning with *X, then it is an old-style hatch. Remove and replace with a new, equivalent HATCH entity. NOTE In addition to the old-style hatch patterns described above, some blocks have been found to contain multiple individual line segments repeated so as to simulate an actual hatch. In such cases, the line segments should be erased and replaced with an appropriate hatch at the appropriate scale. Unjoined Polylines When the endpoints of line or arc segments that form a boundary coincide, it is vastly more efficient to represent the boundary by using a single polyline. For example, a rectangle made of four separate lines should be converted to a single polyline. To do this, use the following procedure: 1 Run the PEDIT command, and select one of the lines. 2 When prompted to turn the line into a polyline, enter y (for Yes). 3 Enter j (for Join), select the other three lines, and press ENTER. In some cases, the join will fail because the endpoints are not coincident, even though they appear to be. If this occurs, use object snaps to carefully reposition the endpoints so that they do coincide. Pixelized Line Segments Some conversion programs create a literal translation of what was on the screen at the time of conversion. This can result in thousands of tiny line segments placed end-to-end, where there should be a single line segment. In such cases, you should trace over the entire course of the end-to-end segments to create a single segment, and then erase all the original pixelized line segments. Blocks and Block Libraries | 2169