# defining ellipses or parabolas using equations

• posted

I have a requirement that needs me to input an ellipse and/or a parabola via a particular set of equations, is there any way to do this in solidworks? does solidworks allow the user to input geometric data via equation?

thanks

• posted

Do a search in the SolidWorks Help file for "equations" and "curves, through XYZ points". The later allows you to import data created in Excel.

John Layne

• posted

Yes. Since ellipses and parabolas are governed by simple equations.

What form of ellipse and parabola equations are you trying to use? Ellipses are easy to govern by major and minor axes. Parabolas have control poits for focus and apex. Also, you can constrain an ellipse or parabola curve to be coincident with predefined points (with positions controlled by dmensions driven by equation).

As for the generic equation control, SW can control any individual dimension by equation. SW is ow also capable of using constants/variables for use in other equations.

• posted

Why not use the equations for an ellipse to find the major and minor diameters and then adjust the dimensions. Plotting points to get built in geometry just doesn't make sense.

• posted

I would add the data directly to the SW database using a simple VB interface, possibly even create an add-in if you do it enough.

Check out the VB calls for parabola and ellipse, then create your VB equations in VB with the appropriate inputs. This would allow you to easily create exactly what you need without worrying about the subtleties of XYZ point splines.

At a minimum I would do what That70sTick and TOP suggested.

Use real geometry not splines when you can.

• posted

Ken

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A good bit of programming, but not always fit for drawing conics (parabolas, ellipses).

Experiment: use eqcurve to draw a y = x^2 curve from x=0 to x=5 with intervals of 1.0 (6 points). In another sketch, overlay a parabola, match spline endpoints and put the focus on the line x=0 (= right plane). You will see that the spline points are in the right place, but the spline curve weaves back and forth across the parabola. Also, the slope of the spline at any given point is not correct (slope of y=x^2 parabola at point x: dy/dx = 2x).

• posted

I wasn't going to post a link to my macro because I didn't think it was appropriate, but someone else did, so I'd better chime in.

As always, there are appropriate ways and times to use tools, and it's not fair to just plug something in at random and say "see, it sucks" and leave it at that.

Splines interpolate between points, and the macro gives you the option to set point density. A spline plotted by points will never be as accurate (particularly at the ends) as the real curve type itself, but the accuracy can be improved by increasing the point density and building it bigger than it needs to be.

Still, I'd draw a regular elipse or parabola and use native SW equations or Excel to locate the axis points and/or center, like other people have already suggested.

Matt

• posted

Defintiely not trying to slam Matt's program. I was 100% sincere when I said it was good work.

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