28 Replies Latest reply on Oct 14, 2008 11:42 AM by 1-8MMYCK

formulas of curve

when we draw any compound curve such as two or three circle that are tangency coincident we obtain any curve,

i wanna learn that new compund curve formulas;

my first message in this forums so may be i cant explain exactly but if any body help me i will be soo happppy,
• formulas of curve
A series of tangent arcs can not be described with a single formula due to discontinuities. It would require a set of discontinuous formulae.
• formulas of curve
i have seen a friend of mine take points off a series of discontinuous arcs from "MATLAB" and create an array.

Once those points are found you can easily import them to solidworks via a design table creating points then use Spline to connect them.

It is not exact but the standard deviation is minimal depending on how accurate you need the curve to be. It is lots of work to do especially if your curve doesn't need to be exact.

Im sure someone else can provide easier alternatives.
• formulas of curve
Roland Schwarz and Ricky Gutierrez thanks for interest,

i will wait another ideas,

and that compound curve is continuous curve (not discontinuous)
• formulas of curve
Selcuk,

I'm not sure if this is of any help to you, but SW has a function called a "Fit Spline" that fits a single spline to a any geometry that you choose. You can control the accuracy of the fit spline. It's in Tools/Spline Tools.
• formulas of curve
I've written macros to go from formula to curve, but curve to formula is more complicated. Like Roland pointed out, you can't describe a series of tangent arcs with only one equation. It is indeed discontinuous in that your curve is given by a series of separate circular equations that share continuous slope (1st derivative), but discontinuous 2nd derivative. However, you can use one formula to describe a spline that approximates those arcs. After forming your arcs, try going over it with a spline that is close to the same shape. After that, extract the XY coordinates of the spline's control points. You might be able to find or write a macro that does this automatically. Using the coordinates of the control points and the TREND() function in Excel (or whatever other software you have available) you can calculate a regression for those known coordinates. If you use Excel, you will have to fit to a function of the form y = m1*x1 + m2*x2 + ... + b, where m1, m2, m3 correspond to x, x^2, x^3 as used in a spline's polynomial equation.
• formulas of curve
Hmm... didn't know about that one, Jerry. Thanks.
• formulas of curve

but i cant send any file;

can anybody help me to send a file to explain what i want;
• formulas of curve
Selcuk,

You have to zip the file before you can attach it. The process to attach a file is tedious. It seems like you have to click a number of buttons to get it done. As I recall, you have to upload the file and then you have to attach it.
• formulas of curve
I would like to see SolidWorks provide a curve-driven equation feature as it already exists in Pro-E, and it would be helpful if SW added this to SW 2009. I believe other SW users have been requesting this feature for a few years.

In Pro-E, datum points from excel can be imported, than a curve can be routed through these points in the X, Y, and Z directions. I assume SolidWorks can do this as well, but I have not tested it. Perhaps the 3D Curve allows the creation of a spline through 3D datum points.
• formulas of curve
Chris, SW is taking baby steps towards the equation driven curve feature. SW2009 has the ability to create 2D splines of the form y=f(x). It's nowhere near as flexible as Pro-E's equation driven curves, but at least it's getting there. If you're looking for similar 3D curve functionality now, you can try this thread.
• formulas of curve

Chris,

You're referring to "TrajPar" (Trajectory Parameters?)

Yes I have asked and I have complained and I have touted the fact that Pro/E had this capability from Day-One, so what's the problem?

Got Me!!!
• formulas of curve
Jerry can you tell me how can i send a zip file as a reply please. i m new user of this forums so please write step one step please if you want to help me;

thanks for everything to everyone

sorry may be this isnt related our question but i have to learn to give more clue in our question and answer
• formulas of curve
1. Click the Attach File(s) button at the bottom of the Reply window.
2. In the Attach File(s) window that comes up, click the Choose button and select the file you want to upload (zip, png, jpg).
4. Now select that file in the file listing and click the green Attach File link.
• formulas of curve
thanks Mahir Abrahim i understood that i use quick reply so i dont see attach button thanks for interest
• formulas of curve
You can email me the file, if you wish, and I will post it for you.
• formulas of curve
thanks for interest charles, now we are in ramadan holiday so i dont have that curve we will start 0n monday. i can send on monday.
• formulas of curve
as others said, you cant get mathematical formulas out of the software, automatically. for the case you have posted, it's easy to obtain the equation manually. if you need the equation of this curve only, i can help.
• formulas of curve
tim, i only need that compound curve equation (formulas) such as y= ax4+bx3+cx2+dx+e . sure starting point is 0,0 it means that e=0

thanks for interest
• formulas of curve
tim and also can you explain how can i obtain that formulas;
i will be soo happy thanks
• formulas of curve
as the curve is compound, the equation is compound too. see below. is this what you are looking for?
• formulas of curve
Tim, you go above and beyond. I like being helpful, but I don't think I'd go as far as doing someone's algebra homework for them
• formulas of curve
Tim,
By the way, what is your avatar? It looks like some Persian flag.
• formulas of curve
yeah thats a persian symbol called Farvahar, which dates back to thousands of years ago. i've seen that in bistoon, http://i16.tinypic.com/4q51pvr.jpg http://www.izadmehr.com/bistoon.katibe.jpg the symbol is carved on a mountain 70m above ground (700 BC) and in persepolis,takht jamshid (515 BC). http://www.bestirantravel.com/...s/shiraz/p_symbol.jpg
• formulas of curve
Does anyone know if its possible to create a curve from an aspheric equation?
• formulas of curve
tim;
firstly thanks for interest and answer,

but i need only one equation so we changed (fit) that single curves as coumpound curve and we obtain a curve called spline,
now i have to learn that spline equation
• formulas of curve
well, you have to search the web to find the general equation of splines. the equation depends on several factors such as selection of degree, knots and spline points, knot weights, and other stuff which i really don't remember now.
that's an interesting problem (for a student).