scan/slice effect problem

[Baldric]

Hello everyone,

 

I am trying to create some kind of "scanning" effect at the moment. For this I want to create a polygon ribbon that wraps around the "scan-object" and that I can move up or down.

Every method I try to do this has some problems though, and I have uploaded with this message a file that demonstrates this.

 

Method 1 was to use a cookie sop. This seems to not be a good method at all, as it appears to be too unstable.

 

Method 2 was using ray sops, projecting two circles onto my geometry, and then finding a way to create the ribbon. In my case I used a rails sop to do this. This method works fairly well. However, depending on the topology of the object, the distribution of points can get very uneven, resulting in areas with too high resolution on the polystrip, and other areas with too low resolution. Can this be fixed in some way? Is there a way to distribute those points along the curves better?

 

Method 3, using clip sops instead of ray sops solves some of the problems of method 2 insofar as it creates much better distribution of points on the curve. However, I haven't been able to find a way to create the poly ribbon with this method because it creates two curves with differing numbers of points, so the rails sop will not work. Is there a way to sample/resample the curves to ensure that I always get equal number of points? And what method is the best to ensure that I sort the points in the upper and lower curves in such a way that connecting them will give nice and predictable geometry?

 

I kind of like method 3, if it would only give me equal number of points... But what if I didn't want to have a straight cut, which is what the clip sop gives you? What if I wanted to have some sort of custom shaped curve to determine the "slicing"? Any good methods for this?

 

I would really appreciate any help!

 

Thanks!

 

Doug

scan_or_slice_effect_problem.hipnc

[edward]

Can you get away with just setting the width attribute on the curve and rendering it? Then you workaround the whole problem of creating the ribbon geometry.

[Baldric]

Thanks for your reply edward,

 

I don't actually think this is desirable in my case. I really want something that is more flexible in use. For example, with a poly ribbon, I could use it to add geometry to specific places, or displacement effects, or transferring attributes etc.. And it would actually follow the topology of the mesh. But for simpler things I guess your suggestion would work, yes.

 

Thanks,

 

Doug

[Rudinie]

Method 2 was using ray sops, projecting two circles onto my geometry, and then finding a way to create the ribbon. In my case I used a rails sop to do this. This method works fairly well. However, depending on the topology of the object, the distribution of points can get very uneven, resulting in areas with too high resolution on the polystrip, and other areas with too low resolution. Can this be fixed in some way? Is there a way to distribute those points along the curves better?

Sure, just resample the curve you got.

Or am i missing something here?

 

Cheers,

[eetu]

I've done something similar by wrapping/raying a nurbs cylinder around the target object and then creeping curves onto that.

A bit like your method #2, but with the nurbs surface you can see what the result will be and you can massage the surface to your liking, e.g. by smoothing.

With some repeated raying & smoothing your can even get your wrapper surface to tuck into nooks in the geometry, which can be hard to achieve otherwise.

[Baldric]

Hi and thanks for your answers!

 

@ Rudinie: Resampling the curve will not really work here. One problem with the ray sop is that the curves I am getting do not conform to the shape of the object properly, especially in those problem areas that has too low a resolution. Resampling after this does mean that I will get a better distribution of points, but the problem of conforming to the shape still remain.

 

@ eetu: That sounds like a novel and interesting approach to me. I will try it out and see what I get, although I am not quite sure if I understand you correctly. How to best wrap a nurbs cylinder around the object? Just with a ray sop, or are more nodes needed? Will this work on deforming objects? 

 

Does anyone else have some additional input?

 

Thanks

 

Doug

[Baldric]

Hello again:

 

@ eetu: I tried your approach, but it seems that I will get exactly the same problem as with my method 2, namely, that you will have certain areas that has too little resolution. Since the nurbs object is a tube there will inevitably be severe stretching in areas that does not conform  well to the topology of the mesh to be "wrapped".  Also, I have to up the resolution of my nurbs tube quite a bit before I get something useful. I'm not sure I understand what you meant by repeatedly raying and smoothing. Could you explain?

 

The images show the issue I am having with my method 2, and also with the method with the wrapped  nurbs surface.

 

Can anyone else help? Perhaps there is a better way?

 

Thanks!

 

Doug