Can’t get sweep to follow extrusion

[Steve Bentley]

Are you using the same spline used for the extrusion? Usually its just an issue with which way your profile object is oriented. If you use a circle (for example) as a profile for the sweep, depending on which way your spline runs, the initial sweep can generate a deflated garden hose looking thing instead of a tube. If you change the circle to an XY orientation instead of the default XZ it usually fixes that right up. For non primitive profiles you can generate that outline in another view (left vs front for instance) or change the axis orientation
with the axis mod tool.
One other thing – if your extrude has rounded endcaps, that can change the overall size of the object and your sweep won’t line up. Just check the constrain button in the caps tab and that will bring the size back to line up with your spline.

[Sean Platt]

Hi Steve,

Thanks for your help. I am using the same spline used for the extrusion. I’ve tried different axis orientations and changing the roundness of the endcaps but nothing seems to be helping that sweep spline lay flush to the extrusion spline all the ay around. I’ve also tried changing the intermediate points options and their number/angle/maximum length to see if that would help but no luck.

[Steve Bentley]

can you upload the file as we’ll take a look?
Also remember that the origin of the profile (even if it’s offset from center) is what rides right along the spline.

[Sean Platt]

Hi Steve. Thanks for your response. The link to the file is here: 11581_sweepissue.c4d.zip.

The area of interest that is causing me problems is the only part with a sweep in this file. Thanks for your help!

[Steve Bentley]

Actually you are using two very different splines located in two very different places to make the sweep and the extrusion. I can’t help get the feeling that you are trying to achieve an effect for which there is a simpler solution.
Can you let me in on the purpose of the sweep? What happens in the animation?

A couple of things here. First, you have a very complex larger spline with a uniform spacing set to 28. You might be better off setting that to adaptive and bringing the number down from 5(the default) down to 1 or 2. that will make sure all the detail of the spline is captured and so you don’t get flat spots on some of the curves. A sure sign of low quality logo is facets on the edges, especially if it goes by close to camera. This is too complex a shape for only 28 knots on the bezier.

While there is nothing wrong with sweeping the way you are, there are a couple of gotchas that might crop up given your geometry. A sweep that comes back around to meet itself can sometimes have a kink at the end point because of the style of spline or because of the handles on that spline. That end point must have the same angle of handle as the start point or the sweep will come charging around on the wrong angle and the two tangents won’t match. With such a big profile compared to the spline shape you will have to watch out for that. And for the same reasons (big profile) when that profile goes around corners on the spline the sweep will often kink because the turning radius needed is smaller than the width of the profile. Usually these kinks (pie wedge shaped errors) are only seen on the inside of the shape or the ends so you might be ok here. A smaller profile width or a smoother more rounded spline is the answer here.

Finally if the outside wall of the sweep is in the same spot as the outside wall of the extrude and they overlap you will get flashing as the two surfaces compete for “who’s on top”.

I’ve fixed the spline to be the right shape, but I’m not sure where the sweep should live. I simply copied the big shape, selected the points I wanted, inverted the selection and then hit delete. Currently the sweep suffering from all of the above. (always they way!) You can move the shape in our out by moving the spline Z and you can adjust the “larger or smaller” than the extrude shape by either scaling your profile or moving the profile’s origin point with the axis modification tool. You can do all these things while the sweep is active so you can judge the effect.

Because the new spline is not in the spot as the non matching spline (in the Z) you may need to move it in and out.

I have a feeling this larger spline was pathed from an image and not drawn as a spline. From a motion graphics point of view, you should be warned that the logo will look “noisy” due to all the ins and outs of the outline. When you take something that was probably a brush stroke or sketchy and apply a hard edged structure to it (the extrude) you magnify the noisyness of the shape. Its kind of like drawing smoke with a marker – you have whispy stuff that you have to put a hard line to. It won’t have the same feel.
The logo may end up looking ragged. It might be better to stylize the shape and smooth some of that out. If you are going to make it reflective those little jaggies may end up making distracting pops and flashes of light instead of a smooth lovely gloss.

11582_11581sweepissuefix.c4d.zip

[Sean Platt]

Wow–thanks Steve for your lengthy response! I need some time to digest all of this since some of this is still sounds foreign to me. I really appreciate the time you put in to helping me with this. I don’t quite understand when and when not to use the different Intermediate Point settings for the Object Properties and what number to dial in just yet. Lots to learn!

[Steve Bentley]

Just think of it as more points means a smoother spline (more resolution)
For uniform, a higher number means more divisions and thefore more resolution- but those are spread out evenly or uniformly so sharp changes in the spline might not have enough points in that spot. You can crank it up to accomodate but the you are adding divisions in spots you don’t need them.

For things like Bezier’s and adaptive it’s about the angle between each point or knot so a lower number has higher resolution. Kind of like (this is over simplified ) whenever the angle between knots rises above 3 degrees stick a virtual point in to make the transition smoother. The adaptive part means if there isn’t enough sharp changes in the curve the system won’t any more geometry – it adapts and adds only as needed.
There is no right or wrong, the only down side is when you come to render the higher the uniform number or the lower the adaptive number means more polys for then render engine to consider.