How to not "blimp" while LOFTING?

[COMJAX]

Why does lofting not do what I want it to do?

I mean if I pick constraints for the command to follow why does it insist on going outside said constraints?

I posted this post in the general section and it was suggested to me that I post a similam thread in this section, so here it is.

How do I control the loft command? (cheese, beer, money; what does it want?)

I need to find out how to connect my rails without the blimping.

It seems once I go over three vertex points thins go all funny.

As an example I'll toss up some pics as I make them tonight.

Example #1

Drawn according Benson Shaw's suggestion in the prior thread with two alterations. 1) I use the Bezier control point option and 2) used 5 pick points though you'll see 7 vertices.

To be continued... more drawing.....just one minute.

[COMJAX]

Next step..Lofting Birail Sweep. I Picked Blue, Red, then Green (Keeping with the direction it has)

Looking at it from the left side everything looks fine.

But when viewed from the front or the top ...............it looks like I'm trying to build a Zeppelin.

Edited September 3, 2007 by COMJAX

[COMJAX]

If I do blue, green, red.

Things look like this.

Top , left , front

Any help would be appreciated.

Thanks.

[Benson Shaw]

Comjax - Looks like you are not gettng any more responses. This will at least put your question back at the top of the list. I thought of a couple more things to try if you know enough about your shape:

Create two or three intermediate rails and loft the whole bunch of them - standard loft, not rail/profile loft.

or

If you have the VW Landscape module, and you know some of the points on your desired surface, you could create a series of rails or 3d loci, like survey topo lines or boat hull strakes (or ribs) and make a terrain from them. Convert that to mesh and manipulate the points if needed.

Or

Compose your three nurbs (two rails and profile) into a single Nurbs curve. Convert a copy to nurbs surface. Add weight and manipulate the intermediate verticies (those not on the rails) to puff it out. You will want to limit the number of verticies. You may have to convert the surface to mesh for your CAM work. Look at the recent thread in this 3d Solids forum on Create Pillows as an example.

or

Hope for some of the 3d wizzards to comment here.

Good Luck

[islandmon]

Check out this kool java tutorial:

http://www.math.ubc.ca/~cass/gfx/bezier.html

The problem of "blimping" is a problem of flattening. VW assumes "normal" NURBS surfaces based on 45? bi-rail controls. What you require is a surface with a flat shallow loft similar to a chamfered chime which does not exceed the bi-rail perimeters. Therefore, high frequency Bezier arcs will need to be replaced with lower frequency 'flat' segmentations. Or a flatter third control curve set at 45? angle prior to lofting. This will reduce but not entirely eliminate the blimping. The more controls the greater the degree of flat.

Example of 2 curves + 1 @ 45? polyline flat rail: