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View Full Version : Offsetting an object along an arc

17th Aug 2011, 06:12 pm
Hi (very first post of mine) and a genuine problem.

I'm trying to offset an object by 3 meters from one end of a long arc to another. How do I offset a point (vertex) or object at a fixed distance along a pre-determined curved line??

Looking forward to your suggestions / advice.:)

ReMark
17th Aug 2011, 06:22 pm
Have you tried either the Measure or Divide command with the Block option?

CyberAngel
17th Aug 2011, 06:43 pm
Welcome to the forum!

I'm not sure exactly what you're asking. If you want to move an object from a point relative to one end of an arc to a point relative to the other end, you could use Rotate with the included angle of the arc. If you want to place objects along an arc 3m from the existing arc, you could offset the first arc and use the second one as a measuring stick, then erase it when you're finished. Another strategy is to use the polar option of Array (with objects) or Minsert (with blocks) to place objects along an arc at specified intervals. As always, a picture would be helpful.

Dana W
17th Aug 2011, 07:03 pm
Hi (very first post of mine) and a genuine problem.

I'm trying to offset an object by 3 meters from one end of a long arc to another. How do I offset a point (vertex) or object at a fixed distance along a pre-determined curved line??

Looking forward to your suggestions / advice.:)

EDIT: after having looked around more I see that cyberangel has already suggested my idea.

If you are offsetting ALONG an arc, look into the Array command. I think it will let you array from one to many items along an arc at evenly spaced increments. If you can't array just one, do two or three and delete the unneeded ones. I haven't tried just one object in an array but I don't have time to test it at the moment to see if it will allow just one.

You may have to do a little math to see how many degrees it takes to cover 3 meters of arc length at your radius.

JD Mather
17th Aug 2011, 07:16 pm
Attach your file here if you can't figure it out.

rkent
17th Aug 2011, 08:11 pm
Welcome and congrats on first post.

Without a lisp routine:
Use measure command, set pdmode to 3 (or see DDPTYPE), you will then have to erase the nodes all along the arc, curve, etc.

Use lengthen command, first copy the arc off to the side, use lengthen, total option, set the value at 3, now pick the arc at the opposite endpoint from where you are needing the object placed. Now you can move the object using the 3m arc as a reference.

Use the attached lsp, not mine.

18th Aug 2011, 12:17 pm
Thanks for all your suggestions. For an internet chat room you're all so kind lol. For those of you who are unclear what I meant I've attached a screen shot of the problem.

In the end I drew a circle from the centre point of the arc, worked out the circumference. (Let's say it was 20meters). I then multiplied 3 meters by 360deg. Divided it by 20meters. This gave me the angle I needed to rotate the lines which I alligned with the first angle point. I then moved the centre point of the objects (in this case circles - they're actually meant to be lights in plan on either side of driveway) to the intersections where the angled increments meet the arc.

Not sure if I've explained that coherently but by looking at image might make it clearer. And thanks to Dana for suggesting 'allign' command that will come in handy in future.

18th Aug 2011, 12:21 pm
By the way....on that note does anyone know how to 'rotate' AND 'copy' a line at the same time. What I mean is..When you rotate a line...You move it! But what if I want to copy it at the same time?

Looking forward to your suggestions. Thanks again.

ReMark
18th Aug 2011, 12:31 pm

18th Aug 2011, 12:51 pm
Mark thanks for the link know how to do it now.:)

JD Mather
18th Aug 2011, 01:18 pm
You can also Rotate and Copy without lisp.
I typically click grip at rotation point and Right Mouse Button Rotate, then RMB again and select Copy, this will create a rotated copy of the original.

ReMark
18th Aug 2011, 01:36 pm
Can also use the Express Tools command MOCORO (Move-Copy-Rotate).

nestly
18th Aug 2011, 01:50 pm
.... does anyone know how to 'rotate' AND 'copy' a line at the same time. What I mean is..When you rotate a line...You move it! But what if I want to copy it at the same time?

You can just use the ROTATE command. After you pick the basepoint, the following is displayed at the command line:

Specify rotation angle or [Copy/Reference]

Dana W
19th Aug 2011, 01:26 am
Thanks for all your suggestions. For an internet chat room you're all so kind lol. For those of you who are unclear what I meant I've attached a screen shot of the problem.

In the end I drew a circle from the centre point of the arc, worked out the circumference. (Let's say it was 20meters). I then multiplied 3 meters by 360deg. Divided it by 20meters. This gave me the angle I needed to rotate the lines which I alligned with the first angle point. I then moved the centre point of the objects (in this case circles - they're actually meant to be lights in plan on either side of driveway) to the intersections where the angled increments meet the arc.

Not sure if I've explained that coherently but by looking at image might make it clearer. And thanks to Dana for suggesting 'allign' command that will come in handy in future.

That was "ARRAY" but you're very welcome. I'll pass the thanks on to CyberAngel who mentioned it first.

Once you know the angle your objects need to be separated by, array is a breeze. Cat got skinned anyway though didn't it. Good luck with the work.