How to use AutoLISP to trim lines ?

Hello,everyone!

I meet a problem when use AutoLISP:

There is a long , straight line going through a circle. I just want to
trim off the part inside this circle ,and of course to remain the
outside part of this line.

Does anyone know how to do that by using AutoLISP? Hope your answer
might be as simple as possilble, I am just a begineer to use LISP.

 

I dont understand, why would you want to use autolisp to do this when the
trim command will do it for you?

 

I can think of two approaches right off.

One is to actually "trim" it by a command call, selecting the two items, and
using a point inside the circle (easily generated from the circle's center

OR

another is to find the intersections of the line and circle, the endpoints
of the line, and erase the original line and create two lines using the
above points.

Both approaches have their challenges.

Have fun, and post some code as you work it out. I'm sure you'll get some
help if needed...

 

(command "trim" "" pt "")
pt must be defined as a varible and be the endpoint of the line to trim.
This line can be placed in your autolisp routine after the endpoint of your
line has been set to the varible pt.

I used this method when I first started learning autolisp but defining the
endpoints
of the lines and drawing the lines from pointa to pointb is a cleaner way to
achieve the
same end result. imo
Although with radii it does involve a bit of math to define the points to
draw the line.

 

How would the line and circle be selected? I can't think of any obvious way
LISP or any other add-on routine could do it faster or with fewer clicks
than the TRIM command.
___

 

I assume it's part of a larger, more complex function that one wouldn't want
to repeat too much.

 

Got that right. I usually don't get around to it since I work in an office
with zero turnover. We just learn to live with the bumps.