6.6 USER DIRECTED CHANGES TO THE GEOMETRIC MODEL

 

• This feature is of the greatest importance to a user

 

• Some onscreen input selection features are,

- Boxes - a good example of this method is the zoom boxes

- Types - all objects of a certain type are selected

- Last - last object created

- All - all visible objects

- Names - in some systems parts are named, and these can be used for reference.

- Markers - symbolic markers can be placed on the screen to allow easy differentiation between object (like in Ideas)

- Layers - drawings can be layered up, which allows easy separation of distinctive parts. One example is a factory layout, including separate layers for machines, plumbing, electrical, HVAC, etc.

 

• Objects often require manipulation on the screen, and certain parameters defined by a number of techniques,

 

- Translation

- select two points (they define a translation vector)

- angle and distance

- select a line (a direction vector)

- move a point to a point

- interpolate

- etc.

- Rotation

- about a pivot point by 1 angle (2 angles for 3D)

- about an axis by an angle

- Mirroring

- mirror over a line/plane

- Magnification

- a magnification about a point by a factor

- Copying

- a simple copy

- a copy with an offset for each copy

- a copy with a rotation for each copy