Iterating over the faces of a component - without exploding

[talig]

Chris - that's what I said: I get the correctnumber of faces. But I make some calculation about them, and I get a different result when I use explode - though I should get the same one. Even a plain box is not working properly.

Fredo - I'm a female
About the coordinates: What you're saying is interesting. I assumed I get the absolute model coordinates in any case. That's obviously true in the exploded case, but possibly the cause of the problem in what I'm trying to do. I'll check it out. Thanks! (and thanks for the to_a tip!)

I already have everything else up and running, so thanks for trying to help - but really, no call for that.
All I need is an array of faces equivalent to that of an exploded component. Nothing more, nothing less.

[Chris Fullmer]

@talig said:

Chris - that's what I said: I get the correctnumber of faces. But I make some calculation about them, and I get a different result when I use explode - though I should get the same one. Even a plain box is not working properly.

Heehe, yeah, I noticed that after I was re-reading some of Fredo's posts. I went back and re-read your post and realized that you already were getting the number of faces correct. My mistake.

@talig said:

All I need is an array of faces equivalent to that of an exploded component. Nothing more, nothing less.

I see what your saying now. Makes sense.

So what is the calculations you're trying to run on the faces? Or maybe you've already got it working with Fredo's great explanation?

Chris

[thomthom]

Have you checked that the list of faces you get is the same as if you exploded them? Not just the number.

[talig]

thomthom - I don't know how I can check that they are the same.
I mean, I can work something out and save the array before explosion, then explode it and compare, but will the object comparison be good enough? Do I need to compare certain fields? I'll obviously need to sort them both to have them in the same order - which may also be non-trivial...
Ideas?

[thomthom]

The .to_s method of entities returns something like: #<Sketchup::Face:0xae3ce28>
You could sort the results of each method, exploded and un-exploded, and write it out to two files. When you have your array just use the .sort method. Then you can compare them for differences. For short lists you can do it yourself. For larger lists if you need to test more complex models you can try with some software that compares two files.

[Chris Fullmer]

I don't think you can .sort a selection set. It always comes back with undefined method '<=>' so I'm guessing they have not built in a way to compare the values of faces to know how to sort them. Even if they implemented sort to work with just the ObjectID string would suffice.

Chris

[Chris Fullmer]

@chris fullmer said:

Even if they implemented sort to work with just the ObjectID string would suffice.

Oh, that works to do that: selection.to_a.to_s.sort

That will sort it by turning all face ID's into a simple string. Then it can sort them. That will come in handy,

Chris

[thomthom]

@chris fullmer said:

Oh, that works to do that: selection.to_a.to_s.sort

I was thinking more like selection.to_a.sort
Is there a .sort method for a string?

[talig]

Thanks thomthom, but who promises that that string is a good identifier, when you run different instances of the program, possibly different files (same model saved under different names), if you have the same component twice in the model? Is it documented anywhere what that hex sequence is? (I'm guessing hash, but even so it matters what it takes into account)

[thomthom]

You're right. Didn't think of that. The Hash, and .entityID changes, also if you explode the groups.

But, another method: You could make a list of the areas of all faces and compare them. Mind you, if any of your groups/components are scaled you have to take that into account.

[talig]

Yeah, I think I've tried that, though only visually.
I'm not sure they match, but visual testing counts for nothing...
I'll give it a go, we'll see what the conclusions are

[Chris Fullmer]

@thomthom said:

I was thinking more like selection.to_a.sort
Is there a .sort method for a string?

Yeah, but that's the thing. There is no selection.to_a.sort method available. But you can sort them alphabetically if you turn all the array items into strings selection.to_a.to_s.sort. Then it sorts them alphabetically.

But of course it was decided this won't help here. But maybe elsewhere in the future.

Chris

[Chris Fullmer]

I'm stilll curious Talig, are looking to find all the face normals? OR looking to find square areas? As Thom and Fredo have mentioned, the different rotation and scale of each group and component need to be taken into account.

Chris

[thomthom]

@chris fullmer said:

Yeah, but that's the thing. There is no selection.to_a.sort method available. But you can sort them alphabetically if you turn all the array items into strings selection.to_a.to_s.sort. Then it sorts them alphabetically.

hmm? .to_s returns an array. And for array objects there's a .sort method. I'm sure I've used this.

[Chris Fullmer]

But it depends what is in the array. Sketchup does not define a heirarchy for how to sort entities like FaceObjects, Component Objects, etc. So the .sort method breaks when put on an array full of items that ruby can't decide how they should be sorted.

I thought that Sketchup.active_model.selection.to_a.to_s.sort would turn the selection into an array, and then turn each objectID into a separate string and then alphabetize all the strings. But thats not quite right. It turns the whole returned array into a single string, and therefore .sort doesn't change anything anyhow.

So to get around it, you have to make an array of all entitiesID's turned into strings. Something like:
sel = Sketchup.active_model.selection selection_strings = [] sel.each do |e| selection_strings << e.to_s end puts selection_strings.sort
That will effectively create an array of strings, instead of unsortable ObjectIDs. The strings can then be alphabetized by .sort, which makes it much easier to compare - even though the entire idea was thrown out a few posts ago. But if you wanted to sort them, this does work.

Chris

[fredo6]

@talig said:

Fredo - I'm a female
About the coordinates: What you're saying is interesting. I assumed I get the absolute model coordinates in any case. That's obviously true in the exploded case, but possibly the cause of the problem in what I'm trying to do. I'll check it out. Thanks! (and thanks for the to_a tip!)

I already have everything else up and running, so thanks for trying to help - but really, no call for that.
All I need is an array of faces equivalent to that of an exploded component. Nothing more, nothing less.

Sorry for the confusion. I missed your splendid avatar.
What I wanted to say is that if you have instances of a component, each containing one face, you will always get the same face object for each one when scanning the model: this is the face which is stored in their Definition. The only way to make a distinction is to use the transformation property of each instance (when you explode you have 2 components, each with its own definition). So, in short, don't expect to get a list of faces alone, but rather a list of couple [faces, transformation].

Fredo

[talig]

Fredo,
Can't I just apply the transformation and save just the transformed face?
Because that's what I thought I'd do

• Tali

[thomthom]

But then you'd apply it to all instances, won't you? Since that face belongs to the definition. This could be what's throwing your calculations off.

What kind of calculations is it that you do?

[AdamB]

@talig said:

Jim - Thanks.
I'm using raytest. But I need a fine-grain detail.
See, if I have a component - raytest will return the component as an answer for the ray hitting any of it's faces. I need to know which face in that component was intersected. More accurately, I need to know that a certain face that should have been intersected, isn't - because it's shaded.

Thomthom - any thoughts?

Thanks again guys,

• Tali

So I've been lurking on this thread and the bit I don't understand is that Model#raytest does return the Face you pick (along with the Component/Group parts hierarchy). Isn't that what you want?

[talig]

AdamB,
No, the calculation that I'm doing is in the reversed direction. I do not want to raytrace the whole model and see what I hit,
I want to select a face (or a few faces) and say how much of it is lit. (i.e. out of the set of rays that should hit it, how many actually hit it first)

This is working great, as already stated, for non-grouped/componented selections...