NVil Forum
General Category => Community Help => Topic started by: Tiles on October 05, 2012, 05:45:32 pm
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What does Select Edges In Empty Faces select? What is an empty face?
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Hi Tiles,
It is based on triangulation and/or the underlying triangulation.
Some pics needed for simple example:)
Created a segmented box:-
(http://i.imgur.com/aElij.jpg)
Selected one of the corner vertex and moved/snapped it to the adjoining vertex.(not welded)
(http://i.imgur.com/RS4WV.jpg)
In sub_object edge mode > "Edges in Empty space" highlights edges:-
(http://i.imgur.com/JO1sj.jpg)
To understand the result, you need to check the underlying triangulation (vertex order/windings)
If I triangulate the object(which shows the underlying triangulation), moving the vertex along the blue arrow to snap it to the adjacent vertex, the 2 edges also move along the red arrows, which cause those 2 moved edges to overlap the other 2 edges.
(http://i.imgur.com/gE0fD.jpg)
That causes 2 triangles to have an edge of zero length, and it can then be said that those 2 triangles are empty, with no visible polygon. The edges selected by "Edges in empty spaces", are the remaining edges of those triangles.
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Thanks Steve. So that`s micro tesselation. The names in Nvil are really killing me :)
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I wouldn't choose the phrase "empty space". At first I had an association of edges from outer space. :)
For me it's more comprehensible if it was called "zero face area" instead of "empty spaces". But then again: if the mesh is not triangulated like in the example with the cube, there are no polygons with zero area, just an edge with zero length.
The more important question for me however is: What is this selection actually good for?!
If I have vertices and edges overlapping I most likely would want to merge/weld them. So what do I do with a selection like this? I'd like to be enlightened, because I can't think of a practical use.
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And it doesn't work for a simple plane or a basic cube?
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But then again: if the mesh is not triangulated like in the example with the cube, there are no polygons with zero area, just an edge with zero length.
The triangulation I made was to show the underlying triangulation that many applications use. Although just about all 3d applications show quads/n-gons, many still have a need for underlying triangulation that they make, usually from the vertex order/windings. It is why it is usually advisable to avoid concave quads (although NVIL uses the term for concave quads for something different)
because I can't think of a practical use.
Then do not use it.
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And it doesn't work for a simple plane or a basic cube?
Just checked on a basic 6 sided cube, and appears to be working correctly.
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Then do not use it.
:D
When i don`t know what a tool is good and meant for, how can i use it then? :)
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Then do not use it.
When i don`t know what a tool is good and meant for, how can i use it then? :)
Did I reply to you, or to your original question of the tools function with "Then do not use it"? No.
My reply was to a specific statement of "I can't think of a practical use" after being shown the use/function of the tool.
So, if you know how a tool functions, but cannot think of a practical way to use it, then do not use it.
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Did I reply to you, or to your original question of the tools function with "Then do not use it"? No.
Huh? Did i attack you? :o
So, if you know how a tool functions, but cannot think of a practical way to use it, then do not use it.
No. The logical conclusion is to ask what this tool is good for then. Which Vaquero did. And which is something that i second. Somebody must have asked for this tool in the past. So there must be a need for it. A case where it is useful. And i am curious in what case this is useful.
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No one asked this tool. It's my own idea. I think it provides a way to check the mesh if you suspect that it may have this kind of geometry and want to find them and fix it if needed.
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I see. Thanks :)
For me it makes no sense to explicitely select this trouble geometry first. You may want to fix it directly. In Blender this does the Remove Doubles Tool. In trueSpace this job does the Heal Vertices Tool. They hunt through the vertices and fix exactly those cases that you select with your tool here, by welding the involved neighbour vertices together.
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The logical conclusion is to ask what this tool is good for then.
Huh?
It is a selection tool that selects what it was implemented for.
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Yes. But what is this selection good for? You cannot work with this geometry in any way.
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Yes. But what is this selection good for?
For doing what it was intended for.
You cannot work with this geometry in any way.
But it is possible to get such geometry inadvertently, possibly as example, when using such tools as "Tweak>move". Would you really want to possibly change poly flow by blindly welding[remove doubles] instead of checking for such bad geometry?
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I see. Thanks :)
For me it makes no sense to explicitely select this trouble geometry first. You may want to fix it directly. In Blender this does the Remove Doubles Tool. In trueSpace this job does the Heal Vertices Tool. They hunt through the vertices and fix exactly those cases that you select with your tool here, by welding the involved neighbour vertices together.
It is not vertex overlap thing so welding may not be your choice to fix it but instead rewinding/optimizing the polygon if you want to keep all the vertices and the shape of the polygon.
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For doing what it was intended for.
I can easily create a ton of tools without any sense or need. They do their job as intended. But they would still make no sense or be any useful. And i would still ask what they are good for.
But it is possible to get such geometry inadvertently, possibly as example, when using such tools as "Tweak>move". Would you really want to possibly change poly flow by blindly welding[remove doubles] instead of checking for such bad geometry?
Simple answer: yes. When vertices are this close that they overlap and build a zero dimension face, then there is already no poly flow anymore. Weld them. And create your needed vertices and edges again. Thats ways faster and accurate than to sort the involved vertices away by hand. This special selection tool doesn`t help you with that anyways.
The point is, why should i explicitely select the trouble geometry with this tool? What can you really do with this selection? For me the answer is: nothing.
As it is now, this tool is a tool without any sense or need for me, wasting space in the menu. That`s why we asked for the useage. For a special case where there is a benefit from it. Not if it does what it is intended for. I have already understood this part very well.
When there`s trouble geometry then i want to remove or to fix it. As fast as possible. So i would simply hit the heal vertices button or the Remove Doubles button. Troublevertices welds away, the zero dimension faces disappears, everything is good again.
It is not vertex overlap thing so welding may not be your choice to fix it but instead rewinding/optimizing the polygon if you want to keep all the vertices and the shape of the polygon.
Hm, a zero face means that all vertices are at the same location. So it is a vertex overlap thing. Else the dimensions of this face wouldnt be zero.
Shape of the polygon is also zero. Why should i want to keep it?
Could you please provide a practical case for this tool?
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When vertices are this close that they overlap and build a zero dimension face, then there is already no poly flow anymore.
Yes, there is still the original poly flow there. Maybe you should check within NVIL before making such a statement.
Weld them. And create your needed vertices and edges again. Thats ways faster and accurate than to sort the involved vertices away by hand.
So you inadvertently create bad geometry, and your way to fix it is to make that bad geometry permanent, then try and find that bad geometry to fix it. Good workflow lol.
As it is now, this tool is a tool without any sense or need for me, wasting space in the menu.
So if a tool makes no sense to you or you do not need it, then it should be removed? Wow!
.
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Hm, a zero face means that all vertices are at the same location. So it is a vertex overlap thing. Else the dimensions of this face wouldnt be zero.
Shape of the polygon is also zero. Why should i want to keep it?
Could you please provide a practical case for this tool?
That's not true. Imagine you have a triangle shape ngon with one vertex at top and the four vertices at the bottom lining up in a horizontal line. If the winding starts from one of the vertices at the bottom, at least one of the faces will have zero area because two of its edges parallel to each other. If the winding starts from the top vertex, problem solved. You may not have the problem before and might never happen to you, but it is a possible thing and some one may need it.
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Could you please stop being so agressive here and put your feelings aside? This doesn`t really help. Thanks.
Yes, there is still the original poly flow there. Maybe you should check within NVIL before making such a statement.
With zero edge lengths. Which means the flow is gone. A mesh flow is defined by the visible faces and edges. Zero dimension faces are not visible anymore. Zero dimension faces are bad geometry.
So you inadvertently create bad geometry, and your way to fix it is to make that bad geometry permanent, then try and find that bad geometry to fix it. Good workflow lol.
No. I remove the bad geometry with one click, and fix the problem by that. That`s what i call workflow.
So if a tool makes no sense to you or you do not need it, then it should be removed? Wow!
Never talked about removing here. That`s your guess, not mine. I ask for a explanation, a user case here. I ask what i can do with the tool. Because the useage for me is zero at the moment.
My answers are still unanswered: What is this tool good for? What can i do with the selected geometry then? Does it help me in any way that i can select this geometry? A practical example please :)
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That's not true. Imagine you have a triangle shape ngon with one vertex at top and the four vertices at the bottom lining up in a horizontal line. If the winding starts from one of the vertices at the bottom, at least one of the faces will have zero area because two of its edges parallel to each other. If the winding starts from the top vertex, problem solved. You may not have the problem before and might never happen to you, but it is a possible thing and some one may need it.
I start to get the idea behind this tool, but this makes still no sense to me. May i again ask for a practical example please? What does it help me here that i can select the trouble geometry? And how do i separate this trouble geometry from possible other zero range faces in the mesh?
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With zero edge lengths. Which means the flow is gone. A mesh flow is defined by the visible faces and edges. Zero dimension faces are not visible anymore.
You are going off an assumption that all polygons are visible, when polygons are defined by the internal geometry database.
As you have not checked, here is an example:-
Elongated segmented box. 2 edges highlight I will move
(http://i.imgur.com/TsiZD.jpg)
There are now 2 quads with zero size faces (blue arrows). I have pre-selected 2 polygons for poly-loop select
(http://i.imgur.com/E5qVB.jpg)
Loop selection then selects all the loop.
(http://i.imgur.com/UYcwl.jpg)
I then weld all overlapping vertex, make the same poly pre-selection and loop select again. This time the loop is limited due to the weld.
(http://i.imgur.com/j6qr0.jpg)
Zero dimension faces are bad geometry.
Yes, and with that tool you can find the edges that belong to those faces.
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I start to get the idea behind this tool, but this makes still no sense to me. May i again ask for a practical example please? What does it help me here that i can select the trouble geometry? And how do i separate this trouble geometry from possible other zero range faces in the mesh?
I can't give you any practival use sample as I am not an artist. I created this tool from theory point of view and imagination.
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I can't give you any practival use sample as I am not an artist. I created this tool from theory point of view and imagination.
There is this little difference between theory and practice as we find out at the moment. That`s why i ask for a practical example. It doesn`t need to be artistic. Programmers art would be enough :)
Isn`t it interesting that even you the programmer cannot provide an example for the use of the tool?
Yes, and with that tool you can find the edges that belong to those faces.
And you can select it with the tool. So far so good. I have long understood this part. But to do WHAT with it then?
That`s the part i still question, and the part where i search for a solution. what is the result of this tool good for? Your images gives a clear picture about the problem. But i still cannot see what the Select Edges In Empty Faces tool could be good for here.
I think we need a break at this point. We go in circles.
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And you can select it with the tool. So far so good. I have long understood this part. But to do WHAT with it then?
That`s the part i still question, and the part where i search for a solution. what is the result of this tool good for? Your images gives a clear picture about the problem. But i still cannot see what the Select Edges In Empty Faces tool could be good for here.
The tools function is to simply highlight the problem area. It is up to you as to what you want to do.
Going from the example I posted above. If a similar problem was on a complex model, the problem may not be easily seen. Your workflow for removing such possible bad geometry would be to weld overlapping vertex(which removes geometry), which could then corrupt polyflow. You would then be checking polyloops visually for any problem, then if found, remove/add geometry to correct.
With using the [Edges in empty Faces]selection first, you can easily see from the readout if any edges have been selected, then edit to correct.
I think we need a break at this point. We go in circles.
Yes, time for me to exit thread.
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The tools function is to simply highlight the problem area. It is up to you as to what you want to do.
So the only real benefit of the tool is indeed just to hilight the trouble areas. Thanks. That`s at least something :)
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Phew, I didn't know this had become such a heated discussion. As it turns out, I couldn't get the selection to work with a simple 6-sided cube due to inaccuracy with the snapping tools. I will post a bug for it.
I get, why this function in general is useful. As I tried to explain, but I guess my point didn't come across: If I have a quad for example, and move two of its vertices together, from the look of it, I now visually got a triangle and the face still has area to be displayed. So this is NOT a zero face area, but bad geometry. Just some "sub-triangle" of the face has no area. I think this is, where the tool in question comes into play. I thought by selecting the edges, that are not of zero length would bring some benefit other than just highlighting. If the edges with zero length would be selected, I wouldn't be able to see them unless I convert them to vertices, but I could decide whether to collapse them, or to smooth them. This seems more practical to me. But from the looks of it, NVIL doesn't have the ability to select edges with zero length (yet).
In a SubD modeller such as Nvil it can happen by accident, that such cases arise (e.g., when working in a higher subdivision), even if it's rare.