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Mike Pauza
02-20-2003, 02:03 PM
Someone told me that modeling cars with "Splines" allows for a lighter mesh than using "Subpatch Splines". Isn't it very much just a matter of preference, with luck/curvature determining how well one method compares to the other shapewise?

Lewis
02-20-2003, 04:51 PM
Hi Mike !

Can you explain me what is "subpatch spline" ???? I'am dealing with splines on daily basis (cars also) but i never heard for that spline :)? I use draw spline or Bezier spline but i never seen "subpatch spline" in modeler ?

luka
02-20-2003, 09:23 PM
maybe he's a secret LW8 beta tester?

faulknermano
02-21-2003, 12:10 AM
Originally posted by luka
maybe he's a secret LW8 beta tester?

that, or he could simply be meaning that the number of segments per patch is reduced so that the resulting mesh is intended for either subpatch (lower poly count) or 'frozen polys' (high polycount. of course, i hope i'm wrong. :D

Mike Pauza
02-21-2003, 10:48 AM
Unless I'm wrong (which may be) , subpatches are either identicle to, or the newest version of LW's old "meta nurb" technology. NURBS stands for "non uniform rational bezier splines". So it's very probably that LightWave's "splines" and "subpatches" are actually both splines and very similiar in function.

I'm not an authority, but I thought that all splines used polynomilas for thier shape ( a + bx + cx^2 + dx^3 + ...), and that the difference between different spline types is the number of polynomials terms used and how cv's are used to control them.

Yes, "LW Splines" have cv's on the surface (which is very nice for shaping them), and Subpatches have cv's typically not on the surface, but IMO the drag tool used with subpatches (on edge intersections) greatly minimizes that disadvantage.

I guess I want somebody with more modeling experience than me to either agree with or refute the statement that using "Spline" or "Subpatches" is completely a matter of preference. It just doesn't seem logical to me that one method is technologically superior to the other.

-Mike

Lewis
02-21-2003, 02:00 PM
Hi Mike !

Now i'am totaly lost in your question :)

IMO Spline is just mathematical line wich can be made from two or more points and she's nice and smooth curved if is BEZIER spline. But SubPatches are used term for POLYGONS IMHO. You can check my Spline patching tutorial for making Cars (all my cars are made with that techique ). Go to www.lwg3d.org

Mike Pauza
02-21-2003, 03:07 PM
Lewis:

I'm sure that huge tutorial will answer all my questions. Now I gotta find time to read it. Interestingly enough, I asked the Spline - SubPatch question in the first place because my brother Rob (the Velociraptor guy) wanted to model some cars and I was arguing with him about how to go about it. :)


Everybody Else:

For anybody that didn't know, Lewis/Elvis is one of the top car modeler's on the planet. When you have some major free time, check out his spline tutorial he mentioned above.

-Mike

Lewis
02-21-2003, 03:23 PM
Hehe Mike yes i know who is Rob ;). Ahh brothers "love" :). I also have brother but he is 6 years younger and not interested in computers so we aren't arguing about such things. But we do about everything else 'coz he is now in his 21 year and he is "smartass" now ;).

You don't need to check whole tutorial to see that teknique - just look at first 50 screengrabs where i finish splines and start spline patching. I'am sure you will understand it pretty quick and since you aren't begginer you will use it in no time :).

Thanks for compliments.

here is direct link for free HTML version of tutorial
http://www.lwg3d.org/forums/showthread.php?s=&threadid=4936

cheers

Castius
02-21-2003, 04:06 PM
I love that lw spines match very close to what sub-d results are. This alows you to combines them very well. What i think makes the differnce when modeling a car is not what to use but where. Some parts of your car might be better suited for sub-d and other might be better meshing it out with splines. So the answer to your isn't which one but where. In harder edged surfaces i try to avoid sub-d at least for a final result as it's to smooth. Using splines to layout the shape then moving on from there is a good way to go about it.

Hiraghm
02-21-2003, 06:26 PM
Ooh. So glad I read this thread. I've been trying to model an automobile car and am having trouble with splines. Also having trouble matching up the backdrop views. I'm going to visit Lewis' website and see if maybe I can learn how to do this. At the moment I'm feeling like a complete moron (with Splinegod cackling evilly over my shoulder...)


Oh no! I get errors. I can't read that page! Halp! :(

SplineGod
02-21-2003, 09:41 PM
For something like a car I would basically lay out the basic mesh with splines. Once patched the resulting polys make a great SubD cage to start detailing from. Since cars are made from discreet panels it isnt necessary to make a car a single seamless mesh. Create the splines along the panel lines.
Splines have a big advantage of not requiring nearly as much data as other methods. They also use less screen real estate and therefore dont cover over the reference. Splines not only define a form but the spline itself determines the edge loops for nice flow.
Splines and SubDs are basied on similar algorythms.

jin choung
02-22-2003, 11:46 PM
ACK!

there's NO SUCH THING as a subpatch spline in lw! actually, i don't think there's such thing as a subpatch spline PERIOD!

whoever wrote that probably got SPLINE confused with PATCH - and technically, i'm not sure if it's even technically correct to say that subdivision surfaces consist in PATCHES....

the splines that we have are the curves from which we can make cages and 'PATCH' to create networks of polys. we do not have any access to actual higher order, multiresolution patches (unlike say Animation Master)... it always results in polys, though we can determine how many polys we get.

METANURBS has nothing to do AT ALL with actual nurbs. and yes, NURBS stands for non uniform rational b-splines. but this is completely a distinct technology from SDS (metanurbs, subpatches).
ADVANTAGES OF SDS OVER NURBS - all nurbs geometry is essentially a SQUARE SHEET or "patch". anything that is not the topography of a deformed square patch must consist of MULTIPLE NURBS PATCHES. this can result in tearing along the seams, especially if you subject the model to a great deal of deformation. in addition, it's also almost impossible to paint a complex NURBS model without a 3d paint app. while it is true that the UV MAPPING is automatically incorporated in each patch, the layout of each patch is rectangular and not at all useful for generating a painting template - like with polys. SDS, like polys can be of completely arbitrary topography and can have as many branching structures as you can think of (and this achieved by simply beveling).
ADVANTAGES OF NURBS OVER SDS - you can TRIM AWAY and CUT APART a curved nurbs surfaces arbitrarily - either with boolean commands or by projecting other nurbs curves onto the surface. YOU CANNOT do the same with any other higher order surface - either SDS or bspline patches... you can also blend together multiple surfaces with a smooth join. this allows you to create a single part that has very complex curving components with radically varying curvatures that nonetheless join together seamlessly (but again, you will likely get a model that consist of multiple nurbs surfaces). this is more of an asset to the precision necessary for industrial design (car chassis, modern products) than it is for organic, natural structures like plants and animals.

the one relation that SDS has with bsplines is that if you allow an sds to become INFINITELY SMOOTH (this theoretical surface is called the 'limit surface'), it is the SAME as a bspline patch.

but once again, bspline patches don't enjoy the advantages that NURBS get (trimming and such).

jin

BTW,

if you've seen the car tutorials on KEYFRAME magazine lately, the advantages of real NURBS modeling something like a car body become INSTANTLY evident. for sections like a hood where you have to drill in details (like 'torpedo hollows' and such), you really have to jump through hoops to connect the joining parts. true, you end up with a single surface if you want but that is a profoundly unimportant 'advantage' in this example. with a true NURBS surface, you could just trim away a proper void for your torpedo hollow and either just join in the new part or blend it in.

but using splines to create LOW DENSITY PATCHES that are later used to create an SDS is pretty good construction method for most circumstances and as evidenced in the keyframe article, it's usable even for cars if need be.

Hiraghm
02-23-2003, 08:42 PM
I got part 2 of that tutorial in issue 27 of Keyframe.. haven't seen Keyframe at B & N since, and just yesterday went on their site and saw the current issue is 31. I was pist. I'm tempted to order the other parts of the tutorial, but I figure I'll be done with my auto by the time they get here. :(