Your mind may have problems visualizing 3D models properly when you view them using the (default) wireframe mode.
- this is even more of a problem for complex 3D models.
Hide is a quick way to improve 3D visualization because it temporarily suppresses lines & edges behind 3D surfaces.
You cannot use realtime options for Zoom or Pan while the display still shows hidden lines removed after using Hide
- but if you use the Regen command you will regenerate the display back to the default wireframe representation.
- you will also return to wireframe mode if you use (non realtime) display commands like Zoom Window or Zoom Extents.
If there are curved surfaces you may want to change the DISPSILH system variable setting (saved in each drawing).
- when DISPSILH=1 (initial value is 0) the silhouette edges of models are displayed and the mesh is also suppressed for Hide.
Several other system variables can be important when you view 3D models in AutoCAD and you can change them using Options.
- increase VIEWRES to make surfaces from ARCs & CIRCLEs (that have thickness) appear smoother on screen.
- increase SPLINESEGS to use more (shorter) straight segments when approximating curved LWPOLYLINE segments.
- increase FACETRES to have smoother meshes on curved surfaces of 3D SOLIDs.
- increase ISOLINES to have more contour lines on surfaces.
You can change these system variables from their initial default values to improve the on-screen quality of 3D model displays
- but you will also decrease system performance & you will notice a greater degradation of performance with larger 3D models.
AutoCAD may sacrifice image quality (temporarily) when you change your display dynamically.
- for example, your model may look like a simple rectangular box when you use Pan in the realtime mode.
- but when you finish using Pan (or stop dragging the display dynamically) you will see the higher quality image again.
You will notice this degradation more when you change system variables (on previous page) or when your 3D models are large.
- your available system resources will also determine how well AutoCAD can dynamically display 3D models.
You can change the default shade mode for 3D models by selecting a different option in the Shademode command.
- when you select a shade mode from this menu, the active viewport remains in this mode until you explicitly change it.
- the Regen command does NOT return the display to the default wireframe mode (as it does after using the Hide command).
- you can even use realtime display options for Pan and Zoom and still retain the selected shade mode display.
Shade modes are saved in drawings.
- when you Open a drawing it will have the same shade modes in each viewport as when you last saved the drawing.
The 2D Wireframe shade mode is the default mode that displays objects using lines and curves to represent the boundaries.
- the standard UCS icon is displayed if UCSICON is On.
- the 3D Wireframe mode is similar to the 2D Wireframe but a 3D UCS icon is displayed instead (if UCSICON is On).
- you will probably create models in one of these 2 modes most of the time because it is easy to see (and snap to) object snaps.
- The Hidden shade mode produces a display similar to what you would see if you use the Hide command
- but this shade mode is continuous once you select it so you do not revert back to a wireframe mode if you use Regen
- and you are also allowed to invoke the realtime options of Zoom or Pan in this mode (you cannot do this when you use Hide).
The Flat Shaded shade mode quickly shades the meshes of models without smoothing effects at the boundary of each mesh face
- whereas the Gouraud Shaded shade mode produces a more realistic image with smoother boundaries between faces.
With edges on you see both the wireframe & shaded image.
- you can use either the Flat Shaded, Edges On shade mode or the Gouraud Shaded, Edges On shade mode.
PRACTICE CHANGING 3D DISPLAY QUALITY
Step 1) Launch AutoCAD (if required). Pick File + Open and select the T302_1.dwg drawing file in your personal folder. Close all other drawings (if other drawings are open).
Step 2) Pick Tools + Run Script. Select the T302.scr script file in your personal folder and pick the Open button there to run this script. This sets several system variables to match the behavior illustrated in this manual.
Step 3) Pick View + Hide to suppress the lines behind surfaces in this simple 3D solid model of a coffee cup.
Step 4) Pick View + Pan + Realtime and observe the command line.
Command: ‘_pan Cannot real-time pan or zoom. Regenerate the drawing.
When you use the Hide command you cannot use realtime options of Zoom or Pan unless you regenerate the drawing first.
Step 5) Pick View + Redraw and notice that nothing happens (the display still shows hidden lines removed).
Step 6) Pick View + Regen to regenerate the current view.
Step 7) Pick Tools + Options. Select the Display tab and check Show silhouettes in wireframe and pick OK.
Many system variables that affect the display quality of 3D models are stored in drawing files (i.e. they are NOT stored in the registry).
Step 8) Pick View + Regen to regenerate the current display using the new setting for DISPSILH.
Step 9) Pick View + Hide again to see how the mesh is suppressed now that DISPSILH is set to 1.
This is a better setting to use when you present or Plot 3D models that have curved surfaces like this.
Step 10) Pick View + Shade + Gouraud Shading.
Step 11) Pick View + Shade + Gouraud Shading.
Right-click in the drawing area to invoke a shortcut and select Pan. Then drag the view slowly to display the shaded cup in another area on the screen then press <Esc> to exit the realtime mode of Pan.
Step 12) Pick View + Regen and notice that the cup is still shaded.
When you select a shade mode the display retains that display mode until you change it.
- this is not the same as using the Hide command to temporarily suppress lines hidden behind surfaces.
You can use realtime options for Pan and Zoom to change the display and the current shade mode is retained
- whereas when you use the Hide command you cannot use these realtime options until the display is regenerated.
Step 13) Pick View + Shade + 3D Wireframe. The UCS icon should still be the 3D version shown below.
Step 14) Pick View + Hide.
Step 15) Pick View + Regen to regenerate the display.
If you invoke the Hide command when shade mode is set to3D Wireframe you will change the shade mode to Hidden.
- this is why the Regen command did not return you to the wireframe display in the previous step.
- you have to select either 2D Wireframe or 3D Wireframe as the shade mode to display the model as a wireframe again.
Step 16) Pick View + Shade + 2D Wireframe.
The drawing is back in the default wireframe mode.
- if you were to invoke the Hide command now you would not toggle to the Hidden shade mode.
Step 17) Save the changes to this drawing then Close the file.