About 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.

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.

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.

Imprecise Geometry

As is the case with unjoined polylines, any endpoints that appear to coincide should actually do so. Small tolerance discrepancies can cause other editing operations to fail. Make sure that geometry that meets visually also meets at a high degree of precision. One way to ensure coincidence is to turn on Nearest, Endpoint, and Midpoint object snap modes, and then adjust the geometry using its grip points.