AutoCAD 3D Modelling:
Before study the 3D modelling, it would be desirable to study the 3D co-ordinate systems.
3D Co-ordinate systems
1. Absolute 3D co-ordinate system:
XY plane is assumed to be parallel to the computer screen. +Z axis is perpendicular to the computer screen projecting towards the user.
A point with co-ordinate 3, 3, 5. Where 3 units along +x axis, 3 units up along +y axis and finally 5 units towards the user (along +z axis).
2. Relative cylindrical co-ordinate system:
A point at 4<30, 5 is marked using relative cylindrical co-ordinate system. 4 units from the last reference point along +x axis, 30 degrees from the x-axis measured
in the anticlockwise directionin the xy plane and 5 units along the +z axis.
3. Relative spherical co-ordinate system:
A point at 5<30<40 is marked using relative spherical co-ordinate system. 5 units from the last reference point along +x axis, 30 degrees from the x-axis measured in the anticlockwise direction in xy plane and 40 degrees up from xy plane.
Types of 3D modelling:
3D modelling is of three types. They are
1. Wire frame modelling
2. Surface modelling
3. Solid modelling
Wire frame modelling:
Wire frame model is a 3D representation of objects by using mostly lines, arcs and circles. It is skeletal and does not have surfaces. Only edge details are shown by a wire frame model.
In surface modelling, the 3D object is made up of opaque surfaces (3D faces). The inner portion of the object is hollow. The details available behind the surfaces are hidden.
In solid modelling, a solid 3D object is produced. It is like a solid object made of a material like wood. The solid thus produced can be cut into pieces. Mass properties of solid models can be determined.
Some of the 3D autocad commands are listed below:
1. Box: box is used to draw three dimensional solid box. The command is BOX. It can be selected from solids toolbar or draw menu – solids
2. Cylinder: cylinder is used to draw three dimensional solid cylinder. The command is CYLINDER. It can be selected from solids toolbar or draw menu – solids
3. Elliptical: The command is CYLINDER. It can be selected from solids toolbar or draw menu – solids
4. Cone: Cone is used to draw a three dimensional cone. The command is CONE. It can be selected from solids toolbar or draw menu – solids
5. Sphere: Sphere is used to draw a three dimensional solid sphere. The command is SPHERE. It can be selected from solids toolbar or draw menu-solids
6. VPoint: VPOINT is used to specify the viewing direction for a three dimensional visualization of the drawing. The command is VPOINT. It can be selected from view menu – 3D view point (Tripod / Vector). Vpoint locates the observer in a specified position to look at the drawing back at the origin 0,0,0.
7. 3D FACE: 3D Face is used to draw a three dimensional face. The command is 3D face or 3F. it can be selected from surfaces toolbar or Draw menu – Surface. 3D face is used to draw a three or four sided surface anywhere in 3D space. Each corner point can be assigned different Z – coordinate values.
8. Elevation: ELEV is used to draw elevation and set extrusion thickness properties of new objects.