can someone please explain splines?

[SEANT]

I agree with JD Mather’s statement. Though, the more common sentiment at large would be that there is almost no design discipline that uses AutoCAD that can’t get by while avoiding the use of splines.

 

With some practice, splines are really not that bad.

[rkent]

The help file is, um, well, helpful.

 

Creates a smooth curve that passes through or near specified points.

 

I use them on electrical and data plan views to show routing. I also use them to show product flow on a plan view for a manufacturing process. There are lots of other uses for them.

[JD Mather]

Rail! I've never used them!

 

 

Rail? Are we talking trains, locomotive tracks? I would think rail routing would be a prime example for the use of splines.

[skipsophrenic]

Rail? Are we talking trains, locomotive tracks? I would think rail routing would be a prime example for the use of splines.

 

Got to admit i tend to work alot more on the civils/structures rather

than the tracks.

 

Platforms/Overhead Line gantries/signalling foundations etc.

 

I do very little in regards to the actual track layout, thats all handled

by a different department, but i'm led to beleive they make extensive

use of polylines and arcs.

[br0604bom]

Nothing against you at all BR, most here are happy to answer any and all questions that come our way - but when you every year see a sudden influx at around exam time of the type "plz help me, plz do this for me, I need this done today, I haven't done anything all year" - then you get a bit leery of questions as your own with no explaination on why you ask them.

 

So don't take any offence at all, I was mearly explaining why I think that Rkent responded like he did.

 

Hope you explore Splines more mate, I don't know a thing about them either

 

No, I won't take offence, just was a bit surprised at what seemd a slightly hostile answer to my question,

 

just glad we have not fallen out so soon after I joined here!

 

and I was not aware it is exam time either, maybe if I had used cad at art school I would not be asking this now!!

 

but yes, I do find the spline topic very interesting, everytime I have previously asked about it people have skirted round the topic,

 

this seems a great site for lots of aspects of autocad which is great after using microstation for a long time,

 

I am passed the dark side now I think!!:-)

[rkent]

My response was not hostile, I guess I should have used an emoticon:) . After seeing three fairly basic questions asked by three different posters it felt like it was homework time again.

 

To all the students out there, if you have any questions to clarify all things AutoCAD this is a great, welcoming forum. What most don't like to see are questions that sound like they are straight out of a text or test. We want people to learn the program as well as how to draft, and not simply pass a test with answers provided.

 

Some simply ask for something to be drawn for them when they should post what they have and ask "how do I draw that angle?", or "how do I draw tangents between those arcs?", etc.

[muddbutter]

I can't express enough my love for splines! I am a drafter for a land surveying company and I use splines all the time. I mainly use them for pools, ponds, creeks, winding sidewalks, etc. It works like a charm...and makes my dwgs look nice and clean. When I come across older dwgs from other people their pools and stuff look nasty compared to mine! I've got SPLINES' back 4 LIFE! lol. yeah im nerdy.

[br0604bom]

rkent,

 

thanks very much for your input, maybe 'hostile' was a bit strong,

and maybe it was because other posts added to it,

 

we are sound,

 

as far as exams times are concerned, not applicable!!

 

very curious on something which seems very obscure but very interesting,

 

mudbutter, you sound a good source for spline questions, I shall be in touch!!:wink:

[ica_cici]

I use spline to draw jewellery design, but I have to trace with 3D pline so I can extrude/sweep it into 3D solid. If there's a tutorial that dig more about spline that will be very helpfull. I guess other beginners agree with me.

[SEANT]

As a visual aid for my earlier posting, the image below shows three splines constructed from the same control points.* Each spline has a different Degree (Order), and a Curvature Graph is displayed to show relative curve intensity at that point – the larger the curve graph spike, the tighter the radius.

 

One trait that may not be so obvious (certainly in the Degree 2) is that when the basis function shifts from one set of points to the next, that juncture is tangent. The change in curvature, however, is extremely abrupt.

 

A car in an open parking lot, driving that path shown in the image, serves as a good analogy. In the degree 2, a change in course would require an instantaneous change in steering wheel position – partial left turn immediately to hard right turn. You can imagine how tough that would be on a passenger.

 

The Degree 3 would be like the steering wheel were sent from it’s left turn position to the right turn position at a constant rate – 90 degree steering wheel turn per second, perhaps. I suspect that is how most of us drive.

 

The smoothest drivers, the high price chauffeurs with any luck, would plan each turn in such a way as to slowly accelerate the steering wheel, giving a lot of feedback to the passengers and allow them to brace accordingly. That would be the Degree 5 track.

 

Even though I claim that an analogy, that does come into play with road and rail design. No doubt “banking” the track allows for a higher degree of abruptness without causing as much disruption to passengers.

 

Rates of change in curvature play a huge role in any Aero/Hydrodynamic application where reduction in turbulence is critical. Splines are not necessarily meant for artistic purposes only.

 

* Note: AutoCAD’s native Spline command creates curves based on FitPoints. The Pedit-Spline then Spline-Object sequence of commands is the only available option for ControlPoint driven spline creation.

ThreeCurves.dwg

[Ryder76]

I do electrical and have never had a need to use spline. The only time I have ever used it was for a survey map I did in school back in the dark ages. We had to do it on the board and in CAD. Preferred CAD!