How to Draw a Parabola in Autocad 2016

1. 2005-01-22,10:21 PM #1

   drawing a parabola

   I am trying to draw a parabola w/ specific dimensions, namely length, maximum width and basepoint width. I've found 2 routines online that might be of use. One, parabola.lsp, can be found at http://www.cadresource.com/library/lispps.html the other, qc.lsp, can be found at http://www.planet-source-code.com/vb....asp?lngWid=13

   However, I have yet to produce the desired length and widths due to my unfamiliarity with the command prompt terminology (e.g., qc.lsp prompts user for 'half focus chord length' and 'centrifuge rate'). So far, I am able to only approximate the desired dimensions by playing around with input values.

   Does anyone know of how I can more accurately draw the parabola?

   Also, please let me know if you are familiar w/ the parameters requested by qc.lsp. I think I can achieve the exact dimensions once I have an equation relating the terms.

   Hi

   Sorry for the *edit* but I believe it would best if the file "quadratic_cv.lsp" was *not* posted on the AUGI web site unless the author has given their permission, please respect the intellectual property of the author.

   "quadratic_cv.lsp" can be found at the following location -

   Plant Source Code

   I have left "parabola.lsp" attached as there is no copyright notice within the header of the file, personally I would rather you remove it, then post the link to where the file can be downloaded from the web.

   AUGI can not take chances with regard any Copyright infringements that might exist + It would be only proper to get the author's permission before posting their work.

   Thanks for your understanding,

   Mike

   Forum Moderator

   Last edited by Mike.Perry; 2005-01-23 at 03:03 PM. Reason: copyright infringement

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2. 2005-01-22,10:29 PM #2

   Re: drawing a parabola

   Hi

   Please note I've *moved* this thread from the New Users Forum to this one as I believe it would be better served here.

   Below snippet is taken from the small print found on the Forum General page ( Click HERE to see a screen capture )...

   <snip>
   New users: Please experiment here with forum features and commands.
   </snip>

   Thanks, Mike

   Forum Moderator

   Last edited by Mike.Perry; 2006-08-07 at 01:36 AM. Reason: Attachment removed.

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3. 2005-01-23,03:00 PM #3

   Re: drawing a parabola

   Originally Posted by ftjaa

   Hi "ftjaa" (sorry I don't know your real name)

   Thanks for removing the AutoLISP files and replacing them with links to where they can be downloaded from the web.

   Thanks, Mike

   Forum Moderator

   Last edited by Mike.Perry; 2005-01-23 at 03:02 PM.

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4. 2005-01-23,04:07 PM #4

   Re: drawing a parabola

   What do you mean by basepoint width?

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5. 2005-01-23,11:51 PM #5

   Re: drawing a parabola

   AKA the width at the center point or origin. I think I wrote 'base point' because that is the term used in qc.lsp. It lies along the line of symmetry in a parabola, near the vertex.

   This is assuming you are using a tangential equation to draw it, though. The origin can also be at the vertex if you are using another equation (e.g., y = x^2^).

   Is that any clearer?

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6. 2005-01-24,02:32 AM #6

   Re: drawing a parabola

   Originally Posted by ftjaa

   This is assuming you are using a tangential equation to draw it, though. The origin can also be at the vertex if you are using another equation (e.g., y = x^2^).
   Is that any clearer?

   Oh. Sure. It all makes sense now. Assuming that you take into account any phase variances of the space time continuum to ensure proper alignment of the tertiary adjunct which would be coplanar to the tangent tangent radius of your parabola you would have your solution.

   Sorry, I just had to do that. Something about math that makes me a little crazy. Actually, I noticed that there is a disscusion board on the site Planet-Source-Code. Have you tried to post a question there too? http://www.planet-source-code.com/vb....asp?lngWId=13

   Either that or perhaps this should be in the Autolisp forum here where this would get more exposure to those that work with lisp? I guess thats where those SUPER Moderators come in handy.

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7. 2005-01-24,03:25 AM #7

   Re: drawing a parabola

   I sent a message to the author of qc.lsp, but I hadn't noticed the discussion board. Thanks for pointing it out.

   This is my first posting and I was not sure which forum was appropriate. I will try moving it to Autolisp if I don't receive much feedback here.

   And sorry for sounding overly complex. What meant was that there are different ways of drawing a parabola, and I was referring to one where a tangent equation is used (x = -y/tan(2pi*y)).

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8. 2005-01-24,04:54 AM #8

   Re: drawing a parabola

   As far as I know, every parabola has a "focus" point and the vertex. The one I think of widens upwards with vertex bellow the focus point.
   What dimensions are those you want to limit this indefinite curve, oriented this way?
   The lisp I wrote some time ago is asking for focus-vertex distance, maximum height and it has adjustable "x" direction increments. It usually goes a bit higher. You just trim it to get the exact height.
   Let me know, if that is what you could use. I am still not quite sure.
   Paul.

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9. 2005-01-24,06:24 AM #9

   Re: drawing a parabola

   Hi,

   alongside the first Figure in this reference:

   http://www.du.edu/~jcalvert/math/parabola.htm

   is a description on how to generate a parabola with a series of tangents which may be useful. (You could automate it with Lisp if you have many to draw).

   FWIW the "centrifuge rate" you mentioned is the eccentricity (e) which equals 1 for a parabola and the "half focus chord length" is a scaling factor dictating where the generated parabola crosses the x-axis , but qc.lsp always draws a parabola in the arc from 45 to 315 degrees which may not be what you want.

   Finally it's possible to APPROXIMATE a parabola with a small portion of an ellipse near either axis if all you want is a smooth curve -or try dragging splines.

   HTH

   Hugh Adamson
   Cadro Pty Ltd
   www.cadro.com.au

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10. 2005-01-24,06:57 PM #10

    Re: drawing a parabola

    Yes, if I am understanding you correctly, those bounding parameters sound as though they match my needs. I am looking for a program that allows me to specify the following:
    1. maximum height
    2. maximum width
    3. focus-vertex distance
    4. width at the focus

    As you suggest, the height can be achieved through trimming, so it is not of great concern. Specifying the width of the parabola at the focus is what might be difficult. I'm not familiar w/ lisp, but when plotting the parabola myself, say in Excel, I use the following equation:
    x = -y/tan(b*y)

    where b is a constant. Using this solution, the focus width depends on b, which makes it easy for me to control. Does your routine use a similar equation? If not, what do you mean by 'adjustable "x" direction increments'?
    Julie

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Source: https://forums.augi.com/showthread.php?13663-drawing-a-parabola

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