Concepts

Groups

In drawings, the same elements are often used repeatedly. The element can be either a single object or several objects placed together in a group. The easiest way of managing objects which belong together in a drawing is to use a group. Groups are made by using Modify > Group > Group Objects. Objects which have been included in a group can only be altered or moved together. The advantage is that you do not have to identify each individual object before altering the group's properties. The application recognizes automatically that it is dealing with a group and reacts accordingly.

If you make a number of objects into a group, Malz++Kassner CAD6 puts the objects into memory and substitutes a reference to these objects in the drawing. A reference like this is known as an instance. The original objects no longer exist on the page. Only an image of them is present. The advantage of this procedure becomes clear when you make a copy of the objects. Each further copy of the group consists of an instance, that is, a reference to the group held in memory. Each instance requires only the same small amount of memory. This makes it possible to manage several large (memory intensive) groups in a drawing using the least possible amount of memory. Instances are saved, along with the group's object information, in drawing files.

When groups are manipulated, this structure is usually not disturbed. Like other objects, each instance has its own set of properties. When an instance is manipulated, only the on-screen representation, not the original objects, are changed. Malz++Kassner CAD6 only applies the alterations to the original objects when an instance is resolved and the original objects are pasted into its place from memory. If the group contains further instances, the changed properties are applied to the relevant instances and fixed into the resolved objects.

Example

Use a simple example to see how a group behaves. Draw an element made up of three basic objects and make them into a group using Modify > Group > Group Objects. To create a group, identify each object to be included in the group in turn. Manipulate this group with commands from the Shape menu. The title bar of the Modify > Object Properties > Edit dialog shows information about the type of object. You can use Modify > Group > Ungroup to break the group up into its individual objects.

Internal Blocks

It is awkward to manage large numbers of repetitive groups, and so Malz++Kassner CAD6 makes it possible to name groups and include them in a list. Each named group can be called as an independent element from the list. These named groups are called internal blocks. Internal blocks are read into a library using Library > Block > Create (Insertion Point) or Library > Block > Create (Frame) As for the command Modify > Group > Group Objects the relevant objects must be identified. To read in an internal block, the library "* Internal Blocks" must be chosen in the dialog, that is, the path must begin with "* Internal Blocks". This is the description for a block which will be saved with the drawing. You can enter a name with up to 64 characters for the block in the "Block:" field. You can then specify using a check box whether the objects which make up the newly saved internal block should remain in the drawing or be replaced by an instance.

To place a block from the list into the drawing, choose Library > Block > Insert and choose an internal block from the list. Make sure that the "* Internal Blocks" library has been selected. Before clicking on OK, you can enter a custom rotation angle and/or scaling factor for the block. The chosen block now "hangs" at the cursor. If the block was read in via frame, then the insertion point will always be in one of the insertion frame's corners. During insertion, the insertion point always lies at the center of the cursor. You should bear this in mind while reading in the block and use a distinctive point as the insertion point. Use snapping when you insert blocks into the drawing.

External Blocks

If a block is stored in an external library, a separate file, then it is known as an external block. Before an external block can be created, a library must be opened or created using Library > Manage Libraries. and clicking on either "New" or "Open" and then entering either a new or existing library name. Click on OK to either open the existing library or create a new library. You can now read a new external block into the library in much the same way as reading in an internal block. You can make use of the commands Library > Block > Create (Insertion Point) or Library > Block > Create (Frame). You must set the correct path to the library in the dialog which appears.

To more clearly arrange internal and external blocks, a hierarchical folder structure, similar to that used for file directories, can be created. To create a folder, use the Library > Block > Edit command.

Figure: Groups, internal and external blocks

It is only possible to change the properties of instances in a drawing. The original, in memory, remains unchanged. Malz++Kassner CAD6 does however make it possible to change the properties of blocks directly. Using Library > Block > Edit you can alter the original (not an instance of the block). Such an alteration will be visible immediately, because any instances in the drawing are based on the altered original in memory. If individual instances in a drawing may not change you can either convert external to internal blocks (Library > Convert External Blocks to Internal), resolve blocks (Library > Block > Resolve Block Instances) or make a copy of the relevant library block (Library > Block > Edit).

Comparison

Groups are the simplest, but most inconvenient way to manage objects which belong together. They are used to protect objects temporarily from alteration or to create simple structures during drawing.

Internal blocks should be used in drawings when it is important to work independently of libraries. Whenever external blocks are used in drawings, it is important to make the corresponding libraries available as well. Internal blocks make it easy to manage elements and prevent the drawing from being changed by accidentally altering a library. Basically, an internal block should be used if an object is only used in one drawing.

External blocks should be used whenever the same block is used in several drawings. Using external blocks ensures consistency, because if an external block is altered then that change is automatically applied to all Instances of that external block in all drawings. After altering an external block, drawings only have to be printed again to get the correct, altered drawings. In addition, the use of external blocks referring to libraries reduces the size of the saved drawing file.

The external blocks in all drawings change, without any form of checking, control, or notification, if the libraries which contain the block definitions are altered. Because of this, the use of external blocks should be thought about carefully!