How to model properly (newbie)

[Anonymous]

I've been wondering is it alright of polygons overlap each other I've been practicing modeling and I've seen tutorial in which they don't overlap polygons but there are times when I view some exercise files especially environment architectural like houses, polygons are overlapping. What if I'm trying to model a house then selling the model online is it alright that they overlap or should I avoid overlapping polygons.

[Anonymous]

Hello,

There are times when it can happen, but the real answer is NO! Never overlap polys!!!!!

A major reason why is that if you render two polys, say a yellow and a blue, you are either going to get yellow or blue showing on the render, or perhaps green (with major luck). two pieces of geometry should never overlap, or share the same space.

Most likely what you have seen are polys that are close, but not quite on top of each other.

Please let me know if this helps, or if you can provide an example that I can help clarify.

[Anonymous]

Hi Matt I really appreciate your reply. Here I have an example Roof Image

In this roof image I overlap the objects and ofcourse polygons will overlap. Should I model the roof as one object or is it acceptable to just overlap the other part of the roof?

[Anonymous]

I've seen plenty of models online with floating geometry like you've demonstrated with this roof. Subscribed to see other people's answers - I'm genuinely curious.

[Anonymous]

@Anonymous

What you are referring to is called intersecting geometry, which is also a bad idea. In my previous comment I was referring to a surface such as two polys that are overlapping on a 2d plane, XY, YZ, etc, it sometimes occurs in rigging, blend shapes, etc... Intersecting geometry is more and more common, but is still a bad idea.

In the case of your roof you will most likely not run into a major issue, but it can happen, and may not be noticeable to most people.

I advise to cut the geometry at the roof intersection. It's very easy to do on a surface like that, as you can do a simple cut and snap to face. There are two reasons for this in your case; first would be that you avoid potential render problems with both your current render and in the future (ideally all artists reuse models), and that then you can fillet your geometry to the roof and make a more accurate model (in roofing the intersections like that are covered by a small tile that keeps the drips out of cracks).

I do like the fact that you are using quads, which is generally a good modeling techinique, but there are a couple points where you should either add a loop, or make a triangle (the roof peaks at either end).

Hopefully you find this useful. It's easy to intersect geometry, but it can cause major problems later, and if you are working in a studio and multiple people rely on your work it can become a nightmare very quickly. Or, in the case of referring back to prior work (houses/roofs, etc are great for this) its easier/better to resolve it now vs later on.

matt

[Anonymous]

@Anonymous

The intersecting geometry is very commonplace. Some studios would accept it, but it's a very lazy modeling method that makes the lighting and rendering more difficult. If you are doing your own animations, A-Z then your will be the one to deal with the errors when/if they occur, but if you pass it off to someone else, then you're going to have a group of people mad at you for the extra work. Is it worth it in a case like this? Not really, it's a simple vertex snap... on a character or blend shape it may be unavoidable.

[Anonymous · Accepted solution]

I posted a response that apparently didn't take... I'm going to abbreviate it, please ask if I skip some points.

What you are referring to is called "intersecting geometry", nor overlapping (faces). Overlapping faces occurs when two faces take up the same space in 2d space (two planes created directly on top of each other). The problem with overlapping faces, which applies to your situation is that the render solution you choose may have a problem determining which piece of geometry is on top. No two render options will react the same....

Intersecting geometry is a "no, no" too. particularly when it's as easy to solve as a roof, which is a straight line... Sure, plenty of tutorials, etc show it, but it's not the correct way of modeling. It happens all to often when you rig a character and move it, etc, and it's always an error. If you were dealing with some crazy curved surface you may get away with faking it, but in this case just do snap to face and move the verts.

In addition, nature, and your roof, will never look correct with a straight edge. Roofs have a tile that covers the sections in question it's curved, in the case of a fillet between the two surfaces to prevent leaks. That effect is easier to achieve if you model it without the intersecting geometry and maybe put an extra edge loop on one, or both surfaces that can be removed later.

Save the intersections until you deal with something complicated! It will happen soon enough. Practicing good technique on simple items like a house will make you the expert when you come up to something complicated later on. Trust me, it seems silly to do it at times if your render looks ok, but it makes the difference between you starting into the industry as a novice vs experienced.

Best of luck! hope it helps!

[Anonymous]

@Anonymous

I wasn't aware of these facts. Thank you for a swift and coherent reply! I'll take note of this for the future but I'm currently a 1st year student where absorbing knowledge about the workspace is paramount. Again, cheers.

[Anonymous]

Hi Matt Thanks I really want to model properly so that I can avoid any issues later on. Here with regards to what you said here in the images so these are overlapping faces? the bottom of the red box and the top of the yellow box is what you called overlapping faces and which is bad for modeling am I right?

[Anonymous]

Here I have another a different version of the roof model 

In the second image you can see that I detached the other part of the roof to reduce poly count is it a good practice?

and in the 3rd image I detached it again because there's no need for detail there.

and lastly the last image is this the fillet that you are referring to?  Again thanks Matt for your replies.

[Anonymous · Accepted solution]

Yes, in this example the bottom face of the red cube, and top of the yellow cube would be overlapping, as they are taking up the same xyz coordinates. You can often see the issues that it can pose when you duplicate a piece of geometry, and don't move it (often seen while rotating the camera).

In the screenshot and render attached I have duplicate geometry that has not been moved, and have highlighted the artifacts caused. In this example I have a piece of road and applied a grass texture to one piece of geometry, and a dirt texture to the other. As you can see, both the viewport, and the render have artifacts caused by the geometry overlapping. This is an unpredictable effect as you can see in the render, as one of the medians rendered just fine, and the other has random faces rendering causing odd triangles and artifacts. These problems would be accentuated in a animation.

[Anonymous]

I wouldn't detach them personally, as it clutters your scene editor and creates more work later on in texturing.

As for the fillet, I used Maya terminology (oops!)... The basic idea is in the screencast I made for you. Obviously I would clean it up more if i were working on this model, but as a quick example... Hope it helps.

Matt

[Anonymous]

Yeah I get it now but what you did in the video why did you separate the chamfered part of the roof? shouldn't it be better if it is one object? and I get it what you said about texturing. I've been practicing a single project and I have like two approach as to how I did it and now I'll do another again. In addition if I'm going to model something if it's going to be one texture then it should be a single object like for example if I'm going to make walls. all the walls should stay as single object? which is proper and will avoid issues?

[Anonymous]

It all depends on what the object is and what the end texture should look like. In the case of roof construction, the main slopes are all tiled the same. Where the edges of slopes meet is usually tiled after the roofers do the flat surfaces, so the texture for those tiles wouldn't line up with the flat surfaces exactly (Google roof ridge/valley). Of course there is a lot of variation in construction, so the modeling technique and texture would vary, but you get the idea.

When determining the proper modeling technique, consider whether or not a texture seam is acceptable, and if the parts are going to be animated. In the case of the walls in a room, either one piece or four pieces would work (walls are an example of detaching geometry to lower poly count; ex. a window on one wall, not the other). For the roof, two pieces would work, so long as they are not the same side. In your example, image #2 creates a texture seam that has to be stitched in the UV editor in order to make a seamless texture. By leaving that side of the roof as a single piece you avoid the stitching step later on in the process. Image #3 would work just fine, as the texture would be expected to start freshly on that side, and not necessarily line up at the peak.

[Anonymous]

Hi Matt you really enlightened me. I even enrolled in some school hoping to learn some do's and don'ts in modeling but well you provided me a concrete answer. Also, with regard to the roof. I totally didn't know, that roof valley and roof ridge thanks for that info. Kudos and accepted solution 🙂 Well next time I believe I'll be having problem with texturing but that's for future problem 🙂

[Anonymous]

Hey Jet, glad I could help, and congrats on the decision to take some classes. Creating geometry can be a fun and challenging process and correct terminology, a bit of research and study of the subject can go a long way. I wish you luck in your endeavors and feel please reach out in the future if you need some more assistance.

[Anonymous]

I think we are here a bit generic about what is or not correct. Techniques should be adapted to the specific needs of the project: engine used, polycount limits, etc. What is OK for a project could be wrong for other. If you decide to avoid any kind of overlapping/intersections regardless of the project it can mean a large amount of extra work. 

For example a very professional technique as modular projects where all is created with libraries are going to need lots of times intersections. Also productivity plugins that create automatic geometry (roofs, plants etc) have plenty of intersections.

For parallel overlapping some projects that can not use layers use it for alpha effects as long the distance between geometries is correct and rendering engine allows it.

[Anonymous]

This is a good point, KarlAkimor, I am guilty of intersecting geometry, and have worked on multiple artist projects that have plenty... It really is about what you can get away with. In the example Jet provided, I have been taught, and learned, that intersecting geometry is not appropriate as it can be easily avoided. Modular projects often have intersecting geometry as the assets are often not created by a single artist, or maybe even team.

[Anonymous]

So you're saying it depends on the project and sometimes you can get away with intersecting geometry? and/or as long as you get the result with no issues that's ok?

[Anonymous]

Hey Jet,

It happens often. I was relating to your project vs more expansive projects. I would never do it on a roof, as its a super easy problem to resolve now, and I would put that model into my files as a "typical" house for use in other projects. Solving the geometry issues now, particularly since it's a simple shape to correct solves not only issues now, but potential future issues when I have a job that I can throw that model into. 

As Karl mentioned, in modular projects, and larger scale, say a neighborhood all of the houses may intersect the ground plane a bit and be ok. That being said, knowing that my house model is ok, the only artifacts I have to look for in a render are at the intersections of the ground plane and the houses, vs every roof, every wall, etc.