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.