Drawing a function or an aproximate of it.

Hello again. Today I'm having a question for drawing a project. This is a barrier, and it's composed by many different elements. there are some lines there, and those aren't a problem, also som circles and arcs. However, there is a small portion of the project that unites 2 element, but, it's shape it's defined by a function of x^2. So I was wondering, How can I draw an aproximate of a parable, or it's exact shape. Thanks a bunch for any help in advance.

Regards.

I am not sure if there is any exact solution, but you may try spline to draw an approximate curve.

1. Suggestion:

Parabola -see: http://en.wikipedia.org/wiki/Parabola

i.e. for the exactly solution : Make a cone and cut it by a plane (first do some math to get the parameters).

Explode the cutted cone and get the exact cutting curve.

2. Suggestion:

See for LWPoly-Approximation

http://www.cadtutor.net/forum/showthread.php?t=49670

Good luck!

Jochen

Another method is to use Excel. put your x in one column and your function for y in the second column. populate the y column by dragging down. Now you have set of x and ys representing your function. import these data to AutoCad and draw the points. If you select enough points, then you can get a rough curve representing exactly the function you have input. This is a mathematical approach and not an easy one for drawing.

If you select enough points, then you can get a rough curve representing exactly the function you have input.

It takes surprisingly few points to create a spline of the curve that is far more accurate than usual tolerance of manufacturing process.

Or use the conic section method.

It takes surprisingly few points to create a spline of the curve that is far more accurate than usual tolerance of manufacturing process.

 

Or use the conic section method.

Say for example I have 5 points, How can I use this as a spline? I mean I enter first point in (-5.3,707) then (-5.1,706) and so on, however using this in the command line makes it so the first point as exact coordinates and the second has -5.1 as x coordinate and 706 as a distance from that point. How can I make it so the second point is an (x,y) coordinate? That being set aside, I'm also having problems entering the end information. It asks for start tangent and end tangent. If I'm drawing 3(x^2) for example or another function with the square potency of x, which are the start and end tangents?

Thanks in advance for everything and to everyone that has posted.

Read Help on absolute and relative coordinates (you want absolute).

For the end tangents you don't need to specify anything in this case (Enter Enter).

Post the cartesian coordinates you want to plot.

Probably the easiest method for you to understand is create the points, then create the spline across those points (node osnap).

Read Help on absolute and relative coordinates (you want absolute).

For the end tangents you don't need to specify anything in this case (Enter Enter).

Post the cartesian coordinates you want to plot.

Probably the easiest method for you to understand is create the points, then create the spline across those points (node osnap).

Thanks for the quick response. I've been reading, about the absolute and relative coordinates, and then my command window. even though I've never inserted @ in the command prompt, when I look at this the 3 command lines are as follows.

Specify first point or [Object]: -5.77,704.28

Specify next point: @-5.53,704.7

Specify next point or [Close/Fit tolerance] : @-3.5,706.36

So, the @ symbol is being inserted without my consent I just press, number.decimals, number.decimals, enter, thus entering relative coordinates and not absolute coordinates as I meant it to be. And the @ is automatically inserted. How can I fix this?

So, the @ symbol is being inserted without my consent I just press, number.decimals, number.decimals, enter, thus entering relative coordinates and not absolute coordinates as I meant it to be. And the @ is automatically inserted. How can I fix this?

Are you really using 2004 version like it says in your avatar?

Enter # to force absolute coordinates.

Are you really using 2004 version like it says in your avatar?

Enter # to force absolute coordinates.

Nope, changed it to 2008 a week ago and forgot to change it in my avatar, sorry for the confusion, will make it right in a minute. And the problem is solved, I had Dynamic Input set "On" that's what was happening. Thanks for all your help, now I'm drawing very smoothly.

2008 (2007?) changed to relative (@) coordinates by default. Thus the # for absolute.

Here

Thanks for your help everyone, the drawing is complete and the work done.