How to make fine curve for trail?

[jungjaehwa]

Hi,

Now I am going to make the Trail a weapon.

Please look at the Attached files.

_Trail.zip

[dbukovec]

hi!

emit particle from a point and use the add SOP to connect them as a line, then use the convert SOP to convert it to nurbs curve, add width attrib to control the width.

[kgoossens]

You could use a polySpline node for this. Spline type to cardinal & double start and end point.( else the spline doesn't go to the begin/end of the curve), but this will not give you a good result. You need to make sure you have higher sampling.

Edited October 19, 2012 by kgoossens

[michael]

or use a trail SOP on a point at the tip - then an add SOP to build your line

HTH

[jungjaehwa]

Thank you ALL so much for your help and support.

As your advise, I am going to try it again and talk more.

I will upload file tested as soon as possible.

Have a great day.

[jungjaehwa]

Hi,

Good morning. It's raining.^^

I spent fine weekend. But I can not solve this problem yet. Oh...My God!

From frame 12 To frame 16, The wand move so fast.

As you can see, In particular frame 13 ~ 15 too fast.

To caculate with polyspline SOP is the key to solve, not exactly.

So I fall in mass how to...

I'd love to find out solution.

Help me please.

trail_v02.hipnc

[kgoossens]

Here is how you can solve it.

TrailExample.hipnc

[jungjaehwa]

Thank you very much indeed.

I have got a idea as looking your attached file.

That is POPnet SOP > source ; Accurate Births.

In my scene, I did not solve that I want to be.

I guess a main problem that between frame 13 and frame 16 so fast moving.

So I tested with ghostTrail plugin on 3DMax.

But the same result.^^

Keep doing untill finding out.

Edited October 22, 2012 by jungjaehwa

[old school]

The issue is so easy to spot once you toggle off Integer Frame Values in the Global Animation Options dialog window and drag the play bar about with sub-frame values.

You can see that the sword is blending linearly between frames. This is a very common issue when you don't have the original motion paths available to you but just the baked out geometry. This linear sub-frame interpolation for fast moving objects is the bane of many RBD, FLIP, Smoke and Pyro, wire and cloth sims where geometry is imported as a sequence of files. This is why we have to take Kim's solution in reservation, but he has the correct idea: You need motion paths! You need to re-construct the proper motion paths for your sword and then re-apply those transforms.

The two tools you will use to re-construct the transforms and do the subframe resampling is the Rivet Object and the Resample CHOP respectively. Rivet works by picking any one, two, three or more points on your target geometry object and it builds object based transforms for you. Fantastic. Sure you can write intriguing Python functions, hscript expressions, vex routines but all will pale in performance compared to Rivet. Use Rivet. Period. Done.

The Resample CHOP works after the Object CHOP fetching the Rivet transforms and providing a fixed cubic sub-frame resample that is rock solid. Most SOP curve reconstruction techniques suffer from popping as the curve is built on-the-fly. Not this method.

If you select one point with Rivet interactively in the viewport, you just get the position transforms. Two points gives you position and direction. Three points or more gives you the full on TRANSFORM (t, r, and s). When selecting three points with rivet, you now get three weight channels to position the rivet pivot where you wish within the plane defined by the three points and beyond the plane.

If your sword has N and up attributes applied at the first frame and the topology is changing but can fix just one point, you only need to select a single point and enable the "Use Point Vector Attributes For Rivet Frame <Of Reference>". You won't get the scale transform with N and up though. Choose whatever as it really doesn't matter for most things.

So this is a four step process (with all kinds of options for tweaking afterward):

1) Geometry object with the File SOP fetching the geometry file sequence off of disk

2) Rivet Object grabbing three points on a part of the model that is topology frame consistent and add the CHOP network to resample the Rivet motion paths.

3) Second Null overridden by the CHOP resampling with a Geometry Object parented and a File SOP only fetching the first frame of the geometry parented to the Rivet Object.

4) A third Geometry Object with an Object Merge SOP to fetch your sword geometry parented to the Rivet Object and then do your monkey magic on the curve at sub-frame intervals how ever you wish: POPs, CHOPs, etc. Your POP solution will work as expected but hopefully not with subframes at 40. Perhaps 3-4 will do.

See the attached file for a working example from your original file/geometry complete with notes as I am sure there are quite a few others out there that don't know about this set-up. It's far easier to see the hip file. Once you get this, there is ample opportunity to streamline things and turn this in to a Houdini Digital Asset or just collapse in to a sub-net.

If the geometry was bending and deforming, then the CHOP network would have to reference in the thousands of points to resample which is also do-able but heavier to handle. Rivet works well for rigid transforming geometry.

----

The Resample CHOP has been used to do sub-frame resampling for raw driven objects as is this example, geometry sub-frame calculations all the way to volume re-timing. The volume re-timing will require you to cut up your volume in to pieces as CHOPs does have an overhead limit (around 40-80k channels but with enough memory...) but I have seen volumes re-timed down 30-60x or more using this technique where each voxel value is sub-sampled and represented by a chop channel with the simple lowly Resample CHOP.

trail_with_rivet_frame_of_reference.hipnc

[jungjaehwa]

Dear Old School,

Oh, Thank you! I am grateful from the bottom of my heart.

Sorry I do not know who you are and your name. Old school...Jeff Wagner?

But I must say "Thank you so much."

I have been doing this issue.

So carefully I read through a lot of views on your professional advice.

I do not know enough CHOP but I am going to study right now.

Let's keep talking about it.

Have a great day.

Jaehwa,Jung