# Thread: Offset along a curve?

1. ## Offset along a curve?

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Here's a problem I keep running into. Maybe there's a command to do it, but I haven't found it.

I have a road with a centerline. I want to offset a line that is perpendicular to the centerline. No problem when the road is straight, but sometimes it curves. Is there a simple way to offset a line so that it remains perpendicular to the curve?

2. Sounds like that would require a lisp routine. Also sounds like it would be a bit tricky to write.

I just use LENGTHEN - TOTAL and click the centreline to get it to shorten to the desired chainage. Then note the coords of the endpoint, then undo to get the original centreline back, then draw a line to those coords.

A bit of mucking around....but it works.

3. When you off set from your center line, are you using the offset command or are you using the copy command? If you are using a spline to get the curves in the road and then you use the offset command it should offset to what ever value you tell it to.

4. If I understand your question...

No simple way. And it may depend if the offset distance is also measured along the curve, or is the straight-line distance between points on the offset object. How do you do it now? My thought was to make a duplicate, then "rotate" the copy, using the "reference" option.

5. ever tried the MEASURE command ?
here's what i would do.

1. turn the entity(ies) that you wish to offset into a block.
2. trim the centreline that you wish to offset along, using the block created in step 1 as your trim line.
3. measure along the centreline you trimmed in step 2, ensuring you click as near as possible to where you trimmed it.
4. enter B (for block).
5. enter name of the block you created in step 1.
6. enter Y for Yes to the question Align with object. (This will ensure your block is perpendicular to your centre-line).
7. enter length along your centre-line that you wish to offset.

Hopefully, the above should give you what you desire, if my interpretation of your initial post is correct.

6. Having read that three times, I suspect what you're trying to do is a 'polar array'

try the array command, and select 'polar'

7. Do you want to offset something at regular intervals along the centreline?

It is quite hard to visualize what you want to do, and perhaps a picture would clarify matters

8. All right, more detail.

The goal is to place contours along a road. If there's an even slope, the contours cross the centerline at regular intervals. They also cross the curbs at a known offset from where they cross the centerline. I'm looking for an easier way to place contours along a curve; it's a simple Offset on a straight section.

At present, I draw an arc of arbitrary length along the centerline from the previous point, use Lengthen to find the proper point, and draw a line to locate the contour crossings. It's clunky, but my previous methods were even clunkier. Sorry, Alan and Norts, I can't change the existing curve because it's a polyline, the road alignment.

Yes, LDD will do it for me. When I get more confident with templates and cross sections, I'll probably do it that way. What I'm doing now is a stopgap.

9. Originally Posted by CyberAngel
Sorry, ... Norts, I can't change the existing curve because it's a polyline, the road alignment.
You can always copy the road alignment and trim the copied part.

If only the horse would take a drink !

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Originally Posted by Norts
You can always copy the road alignment and trim the copied part.!
Yes, but then I'd have to explode it to get the arc I needed, and I'd have the other segments of the polyline cluttering up my drawing. I prefer not to do it that way.

Originally Posted by Norts