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# Drawing curves with equations (epitrochoid)

## Drawing curves with equations (epitrochoid)

(OP)
I am trying to create a shape know as an epitrochoid in CATIA.  I have a few possible approaches: 1) I have created a spread sheet that contains all the X and Y coordinates needed to create the shape (360 points).  How could I use the Excel spread sheet to generate points that I could connect using a spline without have to manually type all the points in?  2) I also have the parametric equations that are used to generate the shape.  How do use these to generate a curve.  The second approach is the preferred.  If it helps to know what the shape looks like please visit http://mathworld.wolfram.com/EpitrochoidEvolute.html

### RE: Drawing curves with equations (epitrochoid)

Hi,
Are you using V4 or V5 ?
If it's V5R9 or above on a PC then the task is simple, check the Help Documentation for "Creating Elements from External Files" and follow it through. It will create Points,Splines or Loft Surfaces from coordinate data.
You will have to write a VBA macro to calculate all the points on the curve that is described by your equation. In this case you have the parametric equation for the evolute of an epitrochoid which is a function of 1 variable (t). I've done this for 0<t<2pi and various values of a,b and h.
Z = 0 will have to be specified in the Excel file.
This has been covered indirectly before in my reply to Thread 560-39970 for calculated surfaces.
If you need the example Excel file and macro it can be sent to you. Then it can be altered for virtually any other curve function that may be required. Even if you are using V4 then the macro shows the method of generating coordinates from the equation.
Cheers,
Dave

### RE: Drawing curves with equations (epitrochoid)

(OP)
Hello...I'm using CATIA V5R7
I would really apprecate the files that you are refering to.
If you could send them to me via email at otx12@hotmail.com I would be very thankfull.

### RE: Drawing curves with equations (epitrochoid)

Hi,
Files sent as requested.
The Catia model is of half a complete Epitrochoid as the limits of (t) have been set at (0,pi) in the macro to illustrate what is happening. For the complete curve edit the limits of (t) in the For Next loop.
I'd like to know if V5R7 supports this method of element creation so please inform me of the outcome.
Cheers,
Dave

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