Types Of 3D Models

You can model real world objects in AutoCAD using a variety of different object types.

3D models can include surface models, solid models or custom objects from other applications.
your task is to choose a model type that best meets your needs and you might even use all types of models in the same project.

Surface Models In AutoCAD

Some industries are well suited to basic surfaces that can be created entirely inside AutoCAD (without additional application software).

for example, 2D floor plans can normally be quickly converted to 3D surface models for presentation purposes.
in some cases changing the THICKNESS property of wall LINEs (to match wall height) is the main 2D to 3D conversion task.

Use the Properties tool to change the THICKNESS property of selected 2D objects.

you can select objects when no command is running then right- click in the drawing area to invoke a shortcut & pick Properties
or you can invoke Properties explicitly and use the Quick Select tool to automatically find objects that match specific criteria.

For example, the simple 2D floor plan below could be converted to 3D by changing the THICKNESS of wall LINEs to 96 inches.

door header LINEs could be moved above the floor by 84 inches (height of the door) and the THICKNESS set to 12 inches.

THICKNESS is always applied in the direction of positive Z for the UCS that was current when the 2D object was created.

for some 2D objects (e.g. CIRCLEs) it will be obvious what the XY plane was when the 2D object was created.
however, LINEs can be created in any plane so it will not always be obvious what the current UCS was when a LINE was created.
you can use positive or negative values for THICKNESS.

CIRCLEs with THICKNESS are like solid cylinders because they have a top, bottom and side surfaces.

even CIRCLEs with zero THICKNESS are opaque and can Hide objects behind them.
DONUTs (circular LWPOLYLINEs with width) have inner, outer, top and bottom surfaces like a section of a pipe.
ARCs with THICKNESS do not have a top or bottom surface.

When LWPOLYLINEs have both THICKNESS and WIDTH you will have surfaces on all sides of the object.

you can specify Width of LWPOLYLINEs when they are created with Pline or when you edit them with Pedit.

TEXT & MTEXT of zero THICKNESS is not hidden by other surfaces but you can assign a small THICKNESS (e.g. 0.001) to avoid this.

You have already seen how to convert a closed LWPOLYLINE into a REGION object using the Region command.

REGIONs are practical 2D surface objects that can be created with 2D shapes that you can draw in AutoCAD.
you can even Subtract internal REGIONs from a larger REGION to create a new REGION with holes in it.

For example, you could create all of the outer surfaces for the simple house model below using REGION objects.

you would orient your UCS in appropriate planes and create LWPOLYLINEs using the Pline command.
any openings (e.g. doors or windows) could be created with LWPOLYLINEs using the Rectang command.
then these inner LWPOLYLINEs could be converted to REGIONs and subtracted from the main REGION for that side of the house.

You can approximate free form surfaces using polygon meshes and AutoCAD lists these objects as POLYLINEs.

these objects may be practical for visualization purposes but cannot be treated as precise surface models in most cases.
if you must model free form surfaces precisely you should consider using the Mechanical Desktop application instead.

Meshes are faceted (not true free form surfaces) and you can influence the size of each facet when you create these objects.

however, you cannot change the resolution of these meshes after they are created
and you cannot snap to centers which limits the usefulness of polygon mesh objects.

The 3dmesh command creates rectangular polygon meshes (in X & Y) with variable positions in the Z direction.

this command is normally used in programs (e.g. grafun.lsp Autodesk sample) that calculate values for X,Y & Z automatically.

The Rulesurf command creates polygon meshes as ruled surfaces between two curves oriented in 3D space.

it is as if you dragged a steel ruler across two curves in 3D to sculpt clay from a model & reveal the “ruled” surface underneath.

The Edgesurf command creates polygon meshes using 4 curves that form an enclosed path.

The Revsurf command creates polygon meshes by revolving a curve about an axis LINE.

The Tabsurf command is like assigning THICKNESS to a 2D curve but the end result is a polygon mesh instead

you select a path curve and a vector direction LINE which determines the direction & distance to generate the mesh.

You can also create primitive shapes as polygon mesh objects by selecting a shape from the 3D Objects dialogue box.

these correspond to the same objects that can be created using the 3d command at the command line.

Solid Models In AutoCAD

Solid models are normally much easier to create & manage than surface models

so you will probably prefer to create solid models rather than surface models most of the time
with the exception of some very basic surfaces (like wall LINEs that are assigned THICKNESS in architectural plans).

Solids automatically acquire a mesh surface when required (e.g. to Shade or Render a model) for presentation purposes

but the true geometrical forms (e.g. hole centers) are retained so you can snap to precise points using standard osnaps.

You can create six SOLID primitives using the AutoCAD command of the same name as the desired primitive.

these primitives are oriented relative to the drawing plane of the current UCS
so you can define an appropriate UCS before creating a new UCS to orient new primitives as desired in 3D.

SOLIDS can be combined using Union, Subtract and Intersect (same boolean commands for REGIONs in 2D are listed on page 6)

for example, you can Subtract a cylinder SOLID from a box SOLID to create a hole in a new SOLID.

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The Extrude command is very practical in solid modeling because you can create many common forms this way.

you can Extrude REGIONs, LWPOLYLINEs or CIRCLEs in a straight line that is perpendicular to the plane of the 2D object
or Extrude these 2D objects along a path instead.

– you can also Extrude using a taper angle which is practical for fabrication methods that require draft angles on surfaces.

You can Revolve REGIONs, LWPOLYLINEs or CIRCLEs to create a SOLID of revolution (e.g. parts to be machined on a lathe).

the angle for revolution does not have to be a full 360 degrees.

You can use the same Chamfer & Fillet commands to edit SOLIDs as you use on 2D objects.

Many solids editing tools are specific to SOLIDs.

these tools range from changing the color of faces & edges (for clarity) to tools for making thin shells from existing SOLIDS.
you will learn more about these tools in the Creating SolidModels

2D drawings can be generated automatically from SOLIDs usingSoldraw & Solprof if you set up a layout using Solview.

you must add your own dimensions but layers are automatically set up to be visible only in appropriate viewports.
you will learn more about these tools in the Generating 2DDrawings From Solid Models

Other Model Types

You do not have to create all of your 3D models in AutoCAD 2000 using the tools described so far in this document.

One alternative is to use an existing library of models for components that someone else has already created.
this would let you make impressive 3D models with only a limited amount of 3D modeling knowledge required.
for example, you could create simple floor plans and insert 3D symbols for the complicated objects (like chairs, desks & lamps)