Symbols: Editing

Blocks and Editing

All instances of a block share the same definition. That saves file space, but it has other consequences too.

One way blocks can be useful is that they can be edited. This might reflect a changing design (e.g. changing from one window design to another) or a more advanced design (e.g. changing from a simplistic schematic-design window to a more complex design-development window) or multi-designer collaboration (you can insert a 'place-holder' window in the elevation while you wait for a more complete version), etc.

Editing a Block

While a block is composed (mostly) of normal data, you cannot see the block definition in the current model, only instances of the block. This makes selecting and modifying it a bit of a challenge. A few programs actually have a separate block editor mode, accessed by double clicking a block instance or selecting an instance and issuing a command. The following technique works universally:

Explode-Edit-Redefine

Block instances can be turned back into normal primitives by exploding an instance. The block definition remains in the model, but now you can "edit an instance" (so to speak). When you are done editing, simply create a new block using the modified geometry and the same name as before. The new definition will overwrite the old one and all existing instances will change as well.

CAUTION! When you re-define the block you will have to re-select the insertion (or "base") point. If it's not the same as before, all existing instances will be drawn in a new place. It is best if you use an osnap to place the instance that you intend to explode, so you can use the same osnap when you set the insertion point. Similarly, use a 1.0 scale factor and no rotation.

Change Propagation

When a block is creating by Inserting a file, the geometry in the original file is copied, not linked. Changing the original file won't (usually) cause the block to change (in Rhino the "Edit > Blocks > Block Manager" can be used to control this behavior). On complex projects with multiple designers, judicious use of blocks and definition updates can make it easier to manage the model.

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