I’m occasionally asked by new users why some smooth objects appear to have straight edges. For example, if they zoom in on a circle they may see a collection of straight line segments making up the circle. This is because internally the circle is represented as a collection of line segments for the purpose of display. In our CAD applications, all objects are displayed as vectors or facets through hardware accelerated OpenGL drivers. Note this is only for display purposes. Everywhere else the exact equation of a circle is used such as in trimming, breaking, or LogiCursor references.
The user can control the object resolution by setting it to one of the following: Coarse, Medium, Fine, Very Fine, Super Fine. Internally these settings control the angular deviation between consecutive line segments. The Fine setting is 11 degrees. The image above shows the various settings for a circle object. The row of circles on top have been exploded into line segments so that you can better see the line segments.
Resolution and Performance
For large files, the resolution you choose may impact your repaint (screen refresh) performance. Generally, your repaint performance in controlled by the number of vectors and facets (used to represent surfaces & solids) that make up the visible drawing. If you’re curious how many vector segments and facets make up the drawing check out the Verify: Object Counts which shows the curve and facet display list sizes.
Setting the Resolution for New Objects
You can control the default resolution of newly created curves, surfaces, and solids through the Preferences dialog box and the Display tab. Simply select the object type and associated resolution. All objects created thereafter will use the new resolution setting.
Changing Existing Object Resolutions
To change the resolution of an existing object, select the Arrow tool and the objects you want to modify. Then pick the Edit:Change Resolution command and select your desired resolution. You can also right click on an object and quickly change it through a popup menu.
Punch!CAD version 7 products introduced a new feature that allows a user to change the definitions of each of the resolution settings. By default the curve resolutions are:
Coarse = 20 degrees
Medium= 15 degrees
Fine= 11 degrees
Very Fine= 8 degrees
Super Fine= 4.5 degrees
A similar set of values exist for facets. However the angle in this case represents the normal deviation between two facets sharing a common edge.
These settings have been selected by the development team to provide the best all around performance for our users.
However, if you have an unusual situation you can change these defaults in the Preferences:Custom Resolutions dialog box. For example, one of our super users described how they use a custom setting while they are creating drawings and another for printing or photorealistic renderings. Changing the settings in the Custom Resolutions dialog box will automatically update all objects to the new setting making it easy to swap between two settings.