Offsetting curves

Offsetting tight curves (curves in the literal sense) often produces unsatisfactory results, but I need to do it quite often. Is there no option but to ‘manually’ fiddle with them?

Hi:
While “Unsatisfactory results” is certainly a valid issue for you, it isn’t a helpful description from a problem solving or support point of view.

Please describe what you are starting with and the poor results you are getting. A small sample file illustrating the problem would be very helpful in this case.

Then we can probably help.

Hi John,

Apologies.

A file is attached. As you can see, when the original curve (outermost to the left) is offset 10mm, the upper bends (what do you call curves in curves?) are fairly smooth and more or less acceptable for my purposes, though not ideal. However the lower ones are kinked. I selected 'smooth' in the offsetting options. Is there anything else I can do to produce a more accurate offset with such curves, other than to 'manually' edit them (and any tips for doing that)?

Thanks for your help,

David Baxter

From: John Brock [mailto:steve@mcneel.com]

Sent: 24 October 2014 17:18

To: dabhander@hotmail.co.uk

Subject: [McNeel Forum] [Rhino for Windows] Offsetting curves

John_Brock

October
24

Hi:

While “Unsatisfactory results” is certainly a valid issue for you,
it isn’t a helpful description from a problem solving or support point of
view.

Please describe what you are starting with and the poor results you are getting. A small sample file illustrating the problem would be very helpful in this case.

Then we can probably help.

To respond, reply to this email or visit http://discourse.mcneel.com/t/offsetting-curves/12728/2 in your browser.


Previous Replies

dabhander

October
24

Offsetting tight curves (curves in the literal sense) often produces unsatisfactory results, but I need to do it quite often. Is there no option but to 'manually' fiddle with them?


To respond, reply to this email or visit http://discourse.mcneel.com/t/offsetting-curves/12728/2 in your browser.

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dabhander, your example file didn’t come through. It sounds like the kinks are occurring because the size of the offset is greater than the minimum radius of the curves. In that situation an accurate offset curve has one or more kinks because of the fundamental geometry. See the attached example. Minimum radius of curvature can be checked using the Curvature command and moving the test point along the curve.
Offset Curves 01.3dm (117.1 KB)

Apologies again, and thanks for your comments. This is the file. However I suspect your answer covers my situation. I suppose I was hoping Rhino would do the hard work and reconfigure the offset curve to create a smooth curve offset uniformly as far as possible the required amount (10mm in this case). However I understand that that would be a very demanding calculation. So I need to adjust the curve myself by moving points until I like the look?

From: David Cockey [mailto:steve@mcneel.com]

Sent: 27 October 2014 15:31

To: dabhander@hotmail.co.uk

Subject: [McNeel Forum] [Rhino for Windows] Offsetting curves

davidcockey

October
27

dabhander, your example file didn't come through. It sounds like the kinks are occurring because the size of the offset is greater than the minimum radius of the curves. In that situation an accurate offset curve has one or more kinks because of the fundamental geometry. See the attached example. Minimum radius of curvature can be checked using the Curvature command and moving the test point along the curve.

Offset Curves 01.3dm
(117.1 KB)

To respond, reply to this email or visit http://discourse.mcneel.com/t/offsetting-curves/12728/4 in your browser.


Previous Replies

dabhander

October
27

Hi John,

Apologies.

A file is attached. As you can see, when the original curve (outermost to the left) is offset 10mm, the upper bends (what do you call curves in curves?) are fairly smooth and more or less acceptable for my purposes, though not ideal. However the lower ones are kinked. I selected 'smooth' in the offsetting options. Is there anything else I can do to produce a more accurate offset with such curves, other than to 'manually' edit them (and any tips for doing that)?

Thanks for your help,

David Baxter

From: John Brock [mailto:steve@mcneel.com]

Sent: 24 October 2014 17:18

To: dabhander@hotmail.co.uk

Subject: [McNeel Forum] [Rhino for Windows] Offsetting curves

John_Brock

October 24

Hi:

While "Unsatisfactory results" is certainly a valid issue for you, it isn't a helpful description from a problem solving or support point of view.

Please describe what you are starting with and the poor results you are getting. A small sample file illustrating the problem would be very helpful in this case.

Then we can probably help.

To respond, reply to this email or visit http://discourse.mcneel.com/t/offsetting-curves/12728/2 in your browser.


Previous Replies

dabhander

October 24

Offsetting tight curves (curves in the literal sense) often produces unsatisfactory results, but I need to do it quite often. Is there no option but to 'manually' fiddle with them?


To respond, reply to this email or visit http://discourse.mcneel.com/t/offsetting-curves/12728/2 in your browser.

To unsubscribe from these emails, visit your user preferences.


To respond, reply to this email or visit http://discourse.mcneel.com/t/offsetting-curves/12728/4 in your browser.

To unsubscribe from these emails, visit your user preferences.

Sqiggle 2 outline with offset.dxf (159 KB)

@dabhander Please do not copy and paste the entire previous post with all replies here, it only creates confusion and makes it very hard to find which is the most recent reply. Everything here is in chronological order, if you want to quote something in a previous post for clarity, select it and use the quote function… Have a look at some other threads on how this works.

–Mitch

Yes, the reason for the kinks in the offset curves is the offset distance is greater than the minimum radius of curvature. Offset does create “a smooth curve offset uniformly as far as possible the required amount (10mm in this case)”. It trims the offset curve where the base curve radius of curvature equals the offset distance to prevent the offset curve from reversing direction. See the attachment for examples of what the entire offset curve would look like if it was not trimmed.

It sounds like you want an offset curve which is modified so that it has some minimum radius of curvature. There is not a simple command which does that so you will need to modify the results of Offset. A simple way to do that is use FilletCorners with the desired minimum radius of curvature. See the attachment for an example.
Offset Curves 02.3dm (152.8 KB)

Hi David,

I appreciate your response. I think I more or less understand the geometry you're talking about, and I'll study and experiment further. Looks like I'll just have to work a bit harder to get what I want!

Thanks again,

David Baxter

From: David Cockey [mailto:steve@mcneel.com]

Sent: 28 October 2014 10:57

To: dabhander@hotmail.co.uk

Subject: [McNeel Forum] [Rhino for Windows] Offsetting curves

davidcockey

October
28

Yes, the reason for the kinks in the offset curves is the offset distance is greater than the minimum radius of curvature. Offset does create "a smooth curve offset uniformly as far as possible the required amount (10mm in this case)". It trims the offset curve where the base curve radius of curvature equals the offset distance to prevent the offset curve from reversing direction. See the attachment for examples of what the entire offset curve would look like if it was not trimmed.

It sounds like you want an offset curve which is modified so that it has some minimum radius of curvature. There is not a simple command which does that so you will need to modify the results of Offset. A simple way to do that is use FilletCorners with the desired minimum radius of curvature. See the attachment for an example.

Offset Curves 02.3dm
(152.8 KB)


To respond, reply to this email or visit http://discourse.mcneel.com/t/offsetting-curves/12728/7 in your browser.

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