Dimension Centerlines

Centerlines on AutoCAD's Dimension Extensions

Contents:
Overview of the Task ---- Looking at an alternative option ---- Conclusion

1Overview of the Task
How many years and how many releases and it still isn't an option. It is one of the most obvious desires for architectural dimensions and yet, after 16 releases we still don't have a simple option for setting the extension lines on our linear dimensions to centerline format. In every office there is another solution for dealing with this problem and the solutions vary from typing CL next to the continue extension line to removing the Extensions and drawing in new Lines that are set to the Centerline linetype. We at ARCHIdigm are guilty of the former technique where we have been typing CL on a continuous linetype extension but the other day I decided to try a new solution for this very old and tired problem and this is what I came up with. Illustrated to the right is an example of the type of solution many of use would like to have and it was created with a color table option rather than an object type or special Lisp solution.
2Looking at an alternative option
Changing the Extension Line Color for a custom Dimension Style Illustrated to the right, I show where you can change the Color of the Extension Lines to something unique that is not used anywhere else in your drawings. When doing this, you should make the change to a copy of the normal Dimension Style so that you have one that uses normal continuous Extension Lines and then one that uses Centerlines.
Setting the Color for the Extension Lines to a fixed Linetype with the Plot Style Table Editor Illustrated to the right I show where you can set the Color specified above, on the Color drop-down list for the Extension Line, and set a permanent Linetype so when it is printed the Color comes out as a unique linetype. By using the Adaptive setting for this Color mapped Linetype ( Long Dash Shot Dash ), the Linetype scale will adjust according to the Zoom/Print scale. .
If you find that this linetype or linetype scale does not work correctly for your needs, you can choose from among the ISO-linetypes or you can use the Apply Global Scale Factor to non-ISO linetypes on the General tab to make further adjustments
3Conclusion
Sometimes anything is better than nothing The main problem with this solution is that you have to use two different dimension styles; one for when you want Extension Lines solid and one for when you want them as center lines. The other problem is that both Extension Lines become centerlines and that may not always be desirable.	Despite the problems, this alternative solution can prove to be rather useful in cases where communicating a lot of centerline dimensions is very important and where drawing a separate line or adding the text CL to each extension line becomes overly tedious. We'll keep looking for better ways to achieve this result.