First copy the circles to other place and change the copied circles property to dashed line. Then do trimming for unecessary part as you needed. Trim also the hidden part of the original one. Move back the trimmed dashed circles to original one using appropriate osnap (ie: center). That's what I would do.

gato richy wrote: I wonder if I can change the properties (let's say line type) in just a part of a line or object. For instance, a circle over a part of another circle. A part of the circle beneath would be hidden. So I would like to change the property of the circle behind  the other, but just the part which is hidden of course. Any help appreciated Richy

What are you attempting to do?  you could make the circle that is "on top" a clear item, so that it obscures the part of the circle below it, that it covers..  or are you attempting to do something else??

Wipeout?  Although only with a Polyline...

which version of ACAD are you using?

Kackac wrote: You can  BREAK the circle at two points, which terminates visible/hidden part of circle. If you want the circle to cohere, make it the group.

I thought 'bout BREAK but in case of circles, it gives you problems. One is that you lose an arc and have to draw it again, tedious when there're many.

Thanks

I'm not sure I understand you well, my english isn't good, but...

gato richy wrote: I thought 'bout BREAK but in case of circles, it gives you problems. One is that you lose an arc and have to draw it again, tedious when there're many.

If you lose a part (rest) of circle, it depend on the direction you select the 1st and 2nd point of break - clockwise or counterclockwise. Or if you mean you lose the part of circle between 1st and 2nd point, this lisp could help you, it break an entity at point, but take care of draw order, it breaks the upper one... Run it typing BP into a command line after apload it into the autocad (If you don't know how to upload it to autocad, ask, I'll help you)

uploads/20081128_224944_break_point.lsp

gato richy wrote: I did just what you said, seems fine when there are no many circles one over another. But with 4 (as I tried today) you lose which line is hidden and which is not.

I'm sorry, bud I don't understand it - why do you have 4 circles one over another?


Edited by Kackac - 28.Nov.2008 at 23:29

Can you specify, what doesn't work, please? What AutoCAD tell you after typing command BP for this lisp?