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Question about modeling cylinder caps


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I just saw a technique for converting the triangles of a  cylindrical caps to quads that I hadn't seen before. Specifically, the modeler used the technique pointed to by the red arrow in the image below to convert the central triangles into quads. He basically created a zig-zag starburst pattern, which cut the number of radial edges in half and created quads as a result.

quads-center.png

Usually, I see people creating quads by just removing every other edge from the radial edges that go to the central pole. The image above could be converted to this form by taking those points around the central point that are closest to it and pushing them away from the center until they are the same distance as the next farthest set of radial points, producing something along the lines of the image shown below.

quads-center-conventional.png

What are the pros and cons of these two modeling approaches with respect to each other - a starburst like pattern as in the top image vs a more conventional circular arrangement as shown in the bottom one.


 

 

 

 

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First of all the top of this cylinder is flat - fully planar, so it doesn't matter if there are triangles or complex poles, even under subdivision.

 

There is no functional difference between the 2 quad options you have shown - they are all kite quads at the centre, and either is an equally acceptable solution for quads on a planar surface.

 

However, both of these ways are rubbish under subdivision on a curved surface - in that case neither will do because you can't be having the complex pole that remains at the very centre, which will result in artefacting during render. In that case then this is the answer for quad solving - it can cope with curving in any direction, and has not a single complex pole anywhere ...

 

image.thumb.png.58e39c122922bacbdd29b24f023ca001.png

 

CBR

 

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Yea to be honest I wouldn't use either of the techniques you provided examples of above flat surface or not, mainly because they're ugly:) one would prefer a nice quad patch like the example @Cerbera provided:D

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1 hour ago, Freemorpheme said:

Why doesnt C4D come with a quad capped cylinder as standard? This would be a monumental upgrade.

Yes that would be nice, although it should have options for both standard and quad caps, as both are useful in certain contexts.

In the meantime we do find that gap in the toolset admirably covered by the HB Modelling bundle, which anyone serious about modelling in Cinema almost certainly will have...

 

CBR

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On 5/23/2020 at 11:16 AM, Freemorpheme said:

Why doesnt C4D come with a quad capped cylinder as standard? This would be a monumental upgrade.

I think it's pretty easy to do this yourself without any plug-ins, although you get a pattern different from the one Cerbera showed. I use a technique that works when the number of Rotation Segments of the cylinder is a power of 2 (i.e., 8, 16, 64, 128, etc...):

1) Create a cylinder making sure that the number of Rotation segments is a power of 2 and Caps turned on with 1 segment. Convert it to an editable object and Optimize if you have an old C4D version to make sure that the caps are attached to the rest of the cylinder (!). For a 16 segment cylinder, you now have something that looks like this from the top, which by now you are quite used to seeing (I selected all of the points in point mode for better visibility):

quad-cyl-caps-img1.thumb.png.4a3624e3e4b25b0605cabd7f94b5a632.png

2) Now, we want to get rid of all but four of the radial edges but keep that central point, as illustrated in the following image:

quad-cyl-caps-img2.thumb.png.62549f6c8ca7e2268f239bcb6d8fd340.png

The quick way I go about doing this, which is especially helpful for cylinders with very many Rotation Segments is to go into Edges Mode and simply use Live Selection with a reasonably sized brush to select all of the edges stemming from the center, by clicking on the point at the center of the cap. You can also just select any radial edge and do a ring select (U~B) on any other radial edge, to select them all, if this way is easier for you.

Then, I just Ctrl-Click the four segments, in Live Select, that form the cross shape I don't want selected (the edges going in the up, down, left, and right directions from the center) which are always constant in number (i.e., exactly four). Finally, the the edges that remain highlighted (as shown in the above image) should now be dissolved (i.e., M~N, Ctrl-BS/Del, Right-Click menu, or however you like to do dissolves).

 

2b) OK, if your cylinder only had 8 Rotation Segments, you're done (congrats!) and you can skip the rest of the steps.

 

3) For cylinders with Power-of-two Rotational Segment counts >=16, we're left with a cap Full-O-NGons at this point, as indicated by the reddish NGon lines in the image below. I've gone ahead and selected the central point in Point Mode for the following step which does most of the remaining work of creating the quad topology:

quad-cyl-caps-img3.thumb.png.fe616b4634d3b38ee4a5bf312b0d5e2a.png

4) In Points Mode, with the central point (and only the central point!) selected we want to do a Bevel operation (M~S) with the settings shown below:

Tool Option

Offset Mode: Proportional

Offset: 100 %

Subdivision: 3 {See Note}

Note: Type a value that is the following function of N, the number of Rotation Segments you started with:

Subdivision=N/4-1.

Since I used 16 segments for this example, 16/4-1=3 for the Subdivision count. (For 32 starting segments, it would be 7, for 64, 15, and for 128, 31) - just divide the starting number by four and subtract one.

Depth: -100 %

Limit: Unchecked (but doesn't matter, int his case)

Shaping

Shape: Round

Tension: 100%

Topology

You can leave all of the Topology options unchecked...

5) We now have the following almost complete topology and I've gone ahead and once again selected all of the points to improve their visibility in the demo image below:  

quad-cyl-caps-img4.thumb.png.c6f7ee384068bb634f440f6c27f2b389.png

6) Unfortunately, NGon lines remain. This is because the Bevel tool slightly "missed" the existing points by a tiny offset, so we are left with doubled points along the cap's circumference that are very close to the points they should be right on top of. It is important to note for the next step that the bad, misaligned points, are the ones that have at least one edge stemming from them and going into the cap and connecting with another point in the interior of the cap. The good original points, are the ones along the circumference of the cap with both edges coming off of them forming said circumference.

7) To fix things up, you can go one of several ways here. These include the fast, easy, but not very accurate optimize operation to help merge all of the duplicate points, all the way to welding each pair of points by hand using the Weld Tool, Stich-n-sew, the Polygon Pen tool, or whatever floats your boat. Personally, I prefer the "by-hand" methods for smaller numbers of rotational segments in order to make sure that the Bevel created points get repositioned and merged to the correctly positioned pre-existing points. For larger Rotation Segment counts, Optimize is you more prudent and pragmatic pal.

Going the Optimize route will tend to merge points at the midpoint between the original, correctly positioned circumference points and their Bevel Tool created pairings. This will slightly shift the original points in the process. On the positive side, the result of this is that the NGons will be gone in a single broad stroke, but the points in the top cap may not line up perfectly with the points in the bottom cap, which may or may not be OK, depending on how this object is used/modeled going forward.

I will describe more specifically my welding approach when precise point positioning is desired, which is often the case for low Rotational Segment counts and/or scenes that require very accurate placement.

I start by switching to Polygons Mode, select all of the polygons in the cap being worked on and then do a "Hide Unselected" command to hide all other polygon geometry of the cylinder and to in effect solo just the polygons of the cap whose points I will be manually optimizing.

Then, in Points Mode, I weld all of the misplaced duplicate points using the Polygon Pen tool (don't forget to check Auto Weld from the Poly Pen options in the Attributes Manager!) to their properly positioned points along the cap's circumference. As previously mentioned, the misplaced points are the ones with edges going into the cap, either towards the center or towards a point int the cap's interior. It would be a good idea to zoom in for precision.

Whichever of the above methods you choose for cleanup, the result is a relatively nice Quad based cap topology, as shown in the image below:

quad-cyl-caps-img5.thumb.png.5bc4f06aa97149c9e7b1b89d35d36cc8.png

I will now include additional images that demonstrate the resulting topology for 32 and 64 Rotational segments, just to give you an idea of what you will get:

32: quad-cyl-caps-img6.thumb.png.951fa0231c70ad3e8c6abc23f895e6c3.png   64: quad-cyl-caps-img7.thumb.png.d3a5b3db30a9c1aa1099699cbc85fcf9.png

It is important to bear in mind that the above images represent flat cap surfaces (and not spherical ones). If there are any negatives to this topological quad-based layout it is the fact that the resulting quads tend to get slightly larger towards the center and smaller towards the original points that made up the initial "cross shaped" edges (i.e., the quads get progressively smaller towards the top, right, bottom, and left edges along the circumference of the cap). You can resize from the center with soft selection turned on to equalize things a bit, but I won't go into that here, since it is a process that would require an article of its own.

 

I hope the above steps help you out, at least until MAXON adds some quality Quad Cap options to cylinders.

 

 

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