easy modeling issue causing trouble
 

hello everyone.....

trying to accomplish a simple task thats causing me a bit of hangups.

so what i want is a shape created from a cylinder. the first pictures gives you an idea of what the shape is (curve projected in RHINO).

now, i want to make this shape in polys. (the final shape should have a thickness, just like a tube).

but i went ahead and tried a couple of different strategies with nurbs intending to convert to polys since that seemed the most straightforward.

1. i have the precise curve i want, so i tried projecting it in maya, and it gave me all sorts of issues like not being able to trim. i think this was because i was projecting a curve that would surround the surface completely by ensuring my curve was = to the diameter of cylinder and this was causing trouble the curve on surface or something...

after trying some other workarounds, i concluded that nurbs in this case was probably not worth it.... unless anyone knows what im doing wrong. again, such an easy task causing issues.

so on to polys..


2. the only way i can think to create this in polys is to create a cylinder with many vertical segments, and drag the CV's to align with the reference curve in a side view.

is this the only / best way to do it in polys?

and if so, is it correct for me to say that working with poly's will most of the time involve aligning things to a reference curve / image instead of having the precision of nurbs and things like projecting exact curve on the surface......

hope to get clear on this,

thanks!

Hi dzcube
I was not sure what I could do so I tryed project curve on surface tool this worked ( on a nurb cylinder), you need to do this from a side or top view not perspective...............dave

PS. sorry just leave a curve on the cylinder what use is that?

thanks,

i was projecting from a side view. i'm projecting so that i can trim....

thats where i'm getting the problems.... it won't trim for some reason

This is really not an "easy modeling issue".

Doing it all in nurbs within maya works; however, nurbs tools in maya are finicky. You can achieve a nice result though.

Converting it to polygons is trickery and has a lot of steps - each of which can cause problems if not done correctly. But in the end you can get a poly surface which you cannot get in Rhno since it's an all nurbs based modeling package.


Here is an outline of the process and some renders...Is this what you are trying to achieve?

http://i181.photobucket.com/albums/x...th_process.jpg
http://i181.photobucket.com/albums/x...reeQuarter.jpg http://i181.photobucket.com/albums/x...reeQuarter.jpg

Let me know if this all makes sense. If you are really confused I can try to make a camtasia video of the process for you.

Here is a similar thread on using booleans and surfaces to create a womans shoe...

http://srv01.simply3dworld.com/showt...threadid=33381

interesting indeed...

i didn't consider booleans because i've run into a heck of a lot of issues with them.

i never know when is an appropriate time or not. in general, i've heard best to stay away from them.

but yeah, i guess there are a lot of steps requiring a careful eye.

so after these suggestions i realized that my starting point will have to be a little bit different. attached are some images of the physical model.

i won't be able to start with a pipe since the top surface will be enclosed......

any ideas?

ah thanks for the actual physical model.

I will toss together something for you and upload the .obj.

Starting with a pipe will still work. I will just close off the top afterwards

Here is a modified version that is very close to what you need.

http://i181.photobucket.com/albums/x...r/th_v2_01.jpg http://i181.photobucket.com/albums/x...r/th_v2_02.jpg
http://i181.photobucket.com/albums/x...r/th_v2_03.jpg http://i181.photobucket.com/albums/x...r/th_v2_04.jpg

and here is the .obj file so you have a starting point. It contains the final object and all the master objects used to slice it up so you can make changes as needed. Best of luck.

Let me know if you have trouble figuring any of it out.

Well actually this is closer (lol).

http://i181.photobucket.com/albums/x...r/th_v2_05.jpg http://i181.photobucket.com/albums/x...r/th_v2_06.jpg

and just out of curiosity, what is the physical object you are modeling? I mean that tube, is it part of a larger overall object?

thanks man! really appreciate it.

it's a design for a plastic bottle in which a cartridge is to be dropped into the bottle, and filled with water (the opening has not be designed yet).... which is why there is a vertical spout at the top....

also, any comments about what i said about bool operations and how many say they should be avoided if possible?

As for booleans. I use them all the time. I have commented several times in this forum that booleans are very useful and powerful tools. They get a undeserved bad rap because folks just don't know how to use them properly.

Just in case you need it. I booleaned the other part of the cylinder.

http://i181.photobucket.com/albums/x...r/th_v2_07.jpg http://i181.photobucket.com/albums/x...r/th_v2_08.jpg
http://i181.photobucket.com/albums/x...r/th_v2_09.jpg http://i181.photobucket.com/albums/x...r/th_v2_10.jpg

and here is the obj.

Here are some smoothed wire frame images...

http://i181.photobucket.com/albums/x...r/th_v2_11.jpg http://i181.photobucket.com/albums/x...r/th_v2_12.jpg
http://i181.photobucket.com/albums/x...r/th_v2_13.jpg http://i181.photobucket.com/albums/x...r/th_v2_14.jpg

yeah, i guess thats the key. knowing how to use them properly.

a few follow questions:

1. in your original instructions on booleans, you say

"8. delete top and bottom caps, delete floating verts"

do you mean by deleting all the individual faces of the cap? if so, how do i easily delete all the vertices that were left behind?

2. and then in #9, you say to cut in half. cut what in half, and why?

3. for number 12, insert extra loops through the "insert edge loop" tool?

4. and as for .obj objects. im having some issues importing them in.
thanks!https://dl.dropbox.com/u/1515390/Scr...03.31%20PM.png

lets start with q4. The message you are getting is my fault I saved the obj file with groups selected. But don't panic all the objects are going to come in and be COMBINED so when you select it will appear as though they are one object.

To separate everything into individual objects pick the object and everything will turn green, from the polygon menu select Mesh>Separate and you should get a group containing all the individual objects.

You will also have a bunch of extra xxxsets in the outliner. You can just select all the xxxsets and delete them all but two will delete.

For questions 1 to 3 I think it will be easier for me to put together a camtasia video for you. This will not take me long and will be easier then trying to type up the answers. I really did not put a lot of detail in the process description so I am not surprised you are a bit confused. Not to worry. Check back here shortly...

Sorry for the delay in getting this uploaded I got side tracked last night.

Here are two videos showing how to use profile curves to make cutting planes to use to cut up a polygon pipe using booleans.

The first video is about 15 minutes and covers the creation of the top section and the second video is only 5 minutes and shows how to create the bottom section for a perfectly fitted completed part.

I dropped the step to split the model in half as it was not necessary.

I hope you find this helpful. Please feel free to ask any questions if anything confuses you.

I am not sure how much bandwidth I have remaining on screencast.com so if I run out and you cannot run the video I will put another copy of both on YouTube.com later today.

Here is what we make:

http://i181.photobucket.com/albums/x...inderTitle.jpg

Here is the link to part 1 - the top section...

http://www.screencast.com/t/YWVjODU5ZDk

Here is the link to part 2 - the bottom section...

http://www.screencast.com/t/NzIxODEyY2

Enjoy! I will post the .obj final file later.

you are the man. :bow:

you rebuild your curves. i hadn't thought of that.

is there any major difference to setting your loft tessellation controls to x number of U's which gives the resulting loft several points as well?

rebuilding the curve seems cleaner and better workflow though.
------

also, when i try to bridge, i get this twisted you see there. however, if i first bride one edge, and then follow with the rest of the surface edge it works.... any idea why?


thanks!

http://dl.dropbox.com/u/1515390/Scre...38.15%20PM.png

is there any major difference to setting your loft tessellation controls to x number of U's which gives the resulting loft several points as well?

Nah, I never really fiddle with changing the "per span # of iso params" to anything other then 1 in U and 1 in V so that it matches the number of cv's in my profile curves. I rarely have need to have more the 1 span in the V direction.

Even when I use this to convert nurbs to poly surfaces I tend to rebuild the nurbs surface with the number of spans in U and V that I want in my polygon surface and then once again convert from nurbs to polygon using general, quad, and 1 for per span # of iso parms in U and V.

I did not spend a lot of time editing the video and I did the narration in a single take just off the top of my head. So I hope you are okay with me sputtering and having occasional points where I had brain lock.

Overall how did you like the video? I am thinking of trying to make more of these if folks find 'em useful. Not sure I am the best of voice talent though. Need to work on my British accent so I can say "Chamfer" and "Al-U-Minium" alot! (smile)

If I get good enough at it I might take a stab at doing a full on modeling tutorial.

Not 100% sure, but I think when you bridge a large set of edges, it has to guess which edge to connect with which, and sometimes it guesses wrong. If you bridge a single pair, then it can use that as a reference for the remainder of the bridging.
In the inner workings, it's probably more due to something like how it sets up arrays containing edge nodes.:confused:

also, when i try to bridge, i get this twisted...

Yes, Stewart is correct. When bridging more then a single pair of edges Maya has to make an educated guess as to how to match the edges and more times then not it chooses poorly (smile).

Not to worry though I pointed it out two times in the video when it happened. Watch the part where I bridge the top cap of the top section and the part where I use "bridge faces" to make the hole in the surface on the top section. Both are in part 1. I record at 2x clip speed so things go by quickly but I figure it's easy to rewind and single step and that is preferable to listening to me chatter on for twice as long at normal speed (smile).

All you have to do is go to the history node for the bridge in the channel box and spin the "bridge offset" parameter until all the edges are paired correctly. Sometimes you have to spin this value to a very high number but it will always eventually line everything up correctly.

ctbram,

the tutorial was perfect. i had no issues following and i got going pretty smoothly.

i've watched many tutorials, and having a voice walk through is crucial. it makes things so much easier.

i look forward to anymore you have coming. maybe i can egg you on with more questions as i develop :)

Oh btw, that sequence of rebuilding curves first with curvature and then with uniform distribution is critical to working with nurbs and curves in maya.

Way back in maya 3 when I started nurbs modeling was the hotness and I spent a lot of time learning to model using curves and nurbs surfaces.

If there was a single word that was the key to the entire universe of using curves and surfaces in Maya it would be "REBUILD", with uniform distribution and 0 to number of spans for uniform curve and surface parameterization.

This one thing "I believe" is the reason so many people get frustrated with nurbs modeling in maya. Having the cv's normalized parametrically (a fancy way of say being numbered in equal integer intervals, i.e. 0,1,2,3...) is critical, essential, imperative, ..., when doing anything with nurbs and curves in maya.

Having non-uniform parameterization will crash fillets, joins, trims, you name it! Before you do any nurbs operation or when in doubt rebuild! AFTER you complete joins rebuild. Follow these two rules and you will have a lot less headaches with curves and surfaces in maya.

excellent,

so.... rebuilding with curvature, thats purely to create the minimum number of CV's right?

what if you forget to do that, but still rebuild it uniformly?


also, at around 9.47 in the tutorial 1... you talk about curve snapping.

if i understand correctly, you are moving that face to match the same Y level as the curve next to it right? now, i still couldn't figure it out. you say press the C key. i changed my mapping, so the C button does something else. however, the curve snapping button is at the top, and i selected it, and moving the selected edges in the Y direction did not snap it to any curves. this has never worked for me.

in your tutorial, i never saw the curve snapping icon pressed, so im not sure what the C key actually did.....

this is one part about maya i never figured out.

thanks

I rebuild with curvature first for two reasons. First it lets me know the minimum number of CV's I could get away with to hold the shape so I have a good idea how many cv's I should use when I rebuild uniformly. Second, there was an annoying bug in Maya and as far as I know it is still there where you would rebuild a curve and it would go all wonky! For some reason rebuilding with curvature first seemed to fix it.

Rebuilding uniformly is important because it ensures that the parameterization (which is a complicated topic) but in simple terms it has to do with the way maya keeps track of cv's internally is normalized, which affect nearly all operations on curves and surfaces. So it is always a good idea to rebuild before using the tools. It is so important that it is one of the very few things I actually dedicate a hot key for. Both rebuild curve and surface.


Ah yes I thought I did a poor job of describing curve snapping. It goes by so fast hard to spit out all the steps before the video is over.

There are three kinds of snapping that I use alot -

Curve (c), grid (x) and vertex (v)

They all work the same.

1. You first select component(s) - verts, edges, faces...
2. then press and hold c for curve, x for grid, or v for vertex snapping (there are icons at the top of the gui for these as well
3. now if you select the y-handle of the move control all movement is constrained to the y-axis, if you select the other handles movement is constrained to their respective axis as well.
4. finally for curve snap, still holding the c key just press the middle mouse button while gesturing over any curve(edge) and all the selected components will snap to the y-value of a point at which you gesture over on that edge.

So in the video I used it to move all the verts on three of four edges to the same y-value of the curve I middle mouse clicked on.

If you hold the v key you press the middle mouse button while gesturing over a vertex

If you hold the x key you press the middle mouse button while gesturing over a grid line

**************************************
THIS IS REALLY IMPORTANT and it's the reason this snapping is hard to describe. You cannot just middle mouse click on an edge you have to middle mouse click AND drag (what I call gesture) over the curve, grid, or vertex for it to work.

***************************************


Two additional notes.

1. You don't have to first constrain the movement by pressing one of the move control handles. In this case all the selected components will snap directly to what you middle mouse gesture over. If you had vertices selected they would all stack to a single point (which is not very useful).

2. There are 2 options that can get you borked if you don't check it. In the move options (double click the move selection icon or press the left mouse button while holding the w key) and be sure "world" is checked (all this snapping stuff only works right in world mode) and the other box is "keep spacing" in most cases I have this box UNCHECKED. If checked the components move but keep their RELATIVE spacing.

One place grid (x) snapping is useful is when you want to move all the verts along the centerline of an object so their x coordinate is at zero. This is important when mirroring objects. You select all the verts, make sure move options is in "world" mode and the "keep spacing" box is UNCHECKED, press and hold the x key, then press the middle mouse button while gesturing over the origin [0,0,0] on the grid and all the verts will .... snap on top of each other to [0,0,0] ...

JUST CHECKING TO SEE IF YOU WERE PAYING ATTENTION....

You have to click the X-handle on the move manipulator to constraint all the points to only move along the x-axis, then press and hold x key, then middle mouse gesture over the [0 0 0] origin on the grid and all the verts will only move to 0 in their x-coordinate and will be aligned on the origin.

exquisite stuff.

i figured out what the issue with the snapping was.

if i want to move a face, i select the face. i then go into curve snapping mode.

gesturing over an edge while middle-click didn't do anything because i had to get out of face mode and go into edge mode.

then, i can middle click + gesture of the edge i want.

slightly unintuitive... since by definition, curve snapping should know i want to snap to anything that is a curve.


also, concerning the "retain component spacing" the help file says :
"Turned on by default. This means that while Maya moves the component, relative spacing is maintained. Turn this option off if you don’t want to preserve relative spacing while translating and snapping polygonal components. "

this is still unclear, since when turned on and off, the result was exactly the same. referring to your tutorial, if i snap the face to the edge, then what relative space would be maintained, the space between the face and the edge? the face moves and the edge stays, so i don't see how anything is maintained.

indeed!

also, after close review, i discovered another subtle issue.

you recommended building curves for curvature first, THEN for unison.

i noticed that when i rebuild my curve for curvature, the shape of the curve changes and is no longer matching as shown from the before and after.... i verified my settings for the rebuild for curvature were identical to yours on the video.

any ideas why this might be occurring?

thanks

I only see one image so I am not really sure what was the cause.

Can you post two images so I can see the change?

I usually rebuild with "curvature" then "uniform".

Rebuilding with curvature gives me an idea of the number of cv's to rebuild uniformly with and fixes a bug in maya where sometimes the curve goes all wonky when rebuilding directly to uniform distribution.

its one image with 2 curves. i cut and pasted both the images onto 1...

let me know if you still don't see it

oh I see them now. I did not notice the scroll bar at the bottom.

Yeah, that happens sometimes and I really cannot explain why. There are very few cv's in the original curve. But I was not able to duplicate it, so a small number of cv's does not seem to be at issue.

When that happens I usually just manually recreate the original curve and that usually fixes it.

Maya nurbs tools have always been a little squirely. I still find them more easy to use then b-splines of other packages though. I really hope autodesk will revamp them and perhaps bring the more robust and "reliable" tools from what used to be studio tools into Maya.

i've heard many times that rhino is better than maya for nurbs. I can understand why, as its a program build for nurbs where as maya is not. Maya is good at lots of things, but not great at anything, apart from being great at being good at a lot of things... errr...


anyway, with the curve thing, wouldn't freezing the transforms and deleting the history before you rebuild the curve, fix that?

Fortunately its one of those things that is an annoyance and does not happen all the time. Usually just recreating the curve and rebuilding fixes it.

Just a heads up, sometimes rebuilding manually is the ONLY fix so don't get to wrapped around the axle fighting it.

It's definitely an internal thing because the only way I know to ALWAYS fix this kind of problem was to export in a format the Autodesk in their infinite stupidity took out of Maya so now you cannot fix it PERIOD without just starting over and building the patch manually from scratch (sigh).

I forget what the export format was but when autoedesk took over Maya they removed it. If you find some old Gnomon nurbs modeling tutorials it's one of the first things they show you - the problem and then the fix export and re-import the model in the magic format and poof the curves rebuild properly.

I guess since nurbs have fallen out of favor that no one at autodesk or alias before them felt it was worth putting any effort in to fix.