How do I create a curve on a surface tangent to 2 other curves already

[lerxst]

How do I create a curve on a surface tangent to 2 other curves already on that same surface. The surface is a simple surface (surf1, curve, curve and the rads are the same). On that surface I have two circles created via Geodesic. Now I want to create a line atngent between those 2 curves on the same surface. How do you do it?

 

[Kapitan]

I've not been near v4 for almost 5 years and I don't remember much about Geodesic but I did find this in a search, see this URL,

http://www-306.ibm.com/software/applications/plm/catiav4/prods/geo/

Surely there is a capability within the Geodesic function to do what your're after. The next picture is a zoom of the Geodesic Menu, it's blurred but most of the options can be made out.
PT PT should give the geodesic path between the circle centres on the support, and PARALLEL or TAP(er) OFFSET will probably give the curves required. All this is from memory, but it should point in the right direction.

For my own interest and amusement I've done this by construction in V5, so that if it had to be done that way, the same method will apply in V4.

Two circles have been normally projected onto the Support and a line that connects their centres ( on the Support ) normally projected to the Support. This Curve is considered to be path of the centre of the tangential curves, which are Parallel curves offset on the Support, by the radius of the original circles, that were directionally projected onto the Support.

In the Thread question, the simple surface is a Surf1:Curve Curve where R1 = R2 and are on parallel planes, with their centres on a common line, so the required Curves can be considered parts of a Helix.

 

[1oldcaduser]

I have never using Geodesic but I would make a line normal to the surface put a normal plane on that and then 'curve1 combine your circles onto the plane. Then make your curves tangent in 2D as required and reverse the procedure to get the curves onto the surface. Check the tangency if you require great accuracy.
You could also try using your new curves to make surf1 cylinders and intersecting them with your original surface.
Have fun

 

[solid7]

That's way too complicated.

The geodesic method is absolutely the way to go.

How is it that you've never used geodesic? This is, according to my estimation, one of the fundamentals of advanced curves and surfacing in V4...

Just curious.




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[catiajim]

Probably because it's one of the more expensive, single functions within CATIA. That, combined with the fact that it's fundamental application, offsetting curves on a surface, should have been a basic part of CATIA in the first place. I mean, who in his right mind would expect anything to work like CATIA's "Euclidian" offset. (And our lofters tell me that CATIA V2 did "geodesic" offsets right out of the box - it wasn't until V3 that the "Euclidian" offset came into being)

 

[1oldcaduser]

I have used catia in many different places in the UK and Europe but have never seen this function anywhere. If ,as catiajim says, it is an expensive licence then that is why because most of the places I have worked are not that large. Maybe it is used mostly in Aerospace. Maybe somebody could tell me otherwise.

 

[catiajim]

I believe that it was originally packaged with a Composites Design license (not Generative Composites - this was way older). Enough people squawked that they wanted Geodesic without Composites that they separated it (circa V3.1.8 or so).

I'm thinking that it was about the same price as a whole design seat, so many folks didn't buy it, even though they were the ones clamoring for it.

 

[solid7]

I guess I'm spoiled. I've always worked on V4 running an "all in one mech" license. (mostly Boeing)

Guess I can chalk this one up to ignorance.




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[Kapitan]

I suppose I've also been spoiled by aerospace and race car companies, they used to have the lot, for surfacing. But in the beginning, for me, in August 1983 there wasn't much I didn't do with Law and Surf2. These two functions used together were very powerful, we did all sorts of developments (Flatwrap) by this method, and this particular case would have been done by setting up the law on a plane to offset the curve, and then creating a new surface on the support surface and keeping the appropriate boundary curve.

Over the years lots of new functions were written and became available, which did these jobs in a slicker way and made life easier. Today in V4, Law and Surf2 don't look much different to Version 1.

On a nostalgic note, this old photograph of the screen shows what Catia looked like in 1983. Black and White only, no fill or colour, no mouse, just a light pen which worked by indicating or selecting elements on the screen. The terminals were IBM3250 and Catia ran on a massive mainframe, alongside Cadam and various analysis software programs.

But, getting back to the Thread topic, Lerxst if you've got Geodesic then I'd be amazed if you can't do what you want, in that function. Perhaps you can let us know.

 

[1oldcaduser]

I cant see the 'burn' point in the middle of the screen.
you didn't need gym with those light pens although I was on CADAM back then. They built a special air conditioned room for the mainframe and had to piledrive the foundations because the site was boggy. We got monitered for performance by 'attentions per hour' and had to log off to take even internal phone calls!