OBJECT types:
- Lines
- Polylines
- Arcs
- Circles
- Splines
- Ellipses
- Hatches
- Text and MText
- Dimensions
- Leaders
- Tables
- Blocks (inserted references)
- 3D solids
- Surfaces
- Meshes
- Point objects
Entries in an object record:
- A unique object ID (handle)
- A type definition
- Geometric data
- Object properties
- Relationships to other database objects
e.g. a record of a line consists of:
- Drawing space (paper or model)
- Layer name
- Start point coordinates
- End point coordinates
- Colour
- Linetype
- Line-type scale
- Lineweight
- Transparency
- Plot style information?
Typical object properties might include:
1. Identification
These define what the layer is.
- Layer Name
- Description
2. Default Object Appearance
These determine how new BYLAYER objects will appear.
- Colour
- Linetype
- Lineweight
- Transparency
- Material
- Plot Style
These are the properties most users think of when discussing layers because they are inherited by objects whose properties are set to BYLAYER.
3. Visibility Control
These determine whether objects are displayed.
- On/Off
- Freeze/Thaw
- Viewport Freeze
4. Editing Control
These determine whether objects can be modified.
- Lock
5. Printing Control
These determine whether objects appear on printed output.
- Plot / No Plot
6. Management Functions
These assist in organizing and controlling complex drawings.
- Layer Filters
- Layer States
- Layer Reconciliation
Typical object property list using BYLAYER
Typical record of an INSERT
Setting Object Properties
Most operators set the properties of objects via the OPTIONS command to BYLAYER or via various layer-property-management commands. This illustrates an important point. An object’s LAYERNAME is a single property assigned to every object by the CLAYER system-variable as it is drawn whether-or-not the OBJECT’S properties are by association with its LAYERNAME (BYLAYER) or assigned directly (By-Object) by relevant commands: CHANGE, CHPROP, LMAN, LAYMATCH.
The facility of assigning a list of properties to an object in one step BYLAYER rather than individually one at a time by CHPROP and the ability to subsequently change the BYLAYER properties of an object by applying a new list of properties is a great time saving facility as well as a means of insuring accuracy and uniformity of object definition. The alternative of applying properties one at a time to objects one at a time is time consuming and prone to error. Each property must be individually nominated but more than one object can be processed at a time.
The object’s geometry and layer assignment are stored properties. They remain unchanged unless deliberately modified by commands such as MOVE, STRETCH, CHPROP, MATCHPROP, LAYMATCH, or editing commands