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Confused about choosing Interpolation and Extrapolation methods in the PWS


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Hey Hashers,

Didn’t think I would be back so soon with another question (s). I tell ya, I was doing just fine breezing through this book until I got to Action Basics. This is deceptively the shortest chapter in the tome, yet it’s the one that’s caused the most head scratching.

Ok, so I tried to scan the part of the book that's befuddling me and upload it here, but that's just not working out for me. I will retype it:

   “Each driver has it’s own setting for it’s default interpolation, located in the PWS next to the name of the driver. There are actually three pull-down menus located under that image, the first and last of which look ghosted out and are for extrapolation methods (which we discuss next) while the center is for the interpolation of the channel in question. Changing the interpolation method affects the entire channel. If you do not want that, change individual points or groups of points to any interpolation method by bringing up the contextual menu for a selected group or a single control point in the Channel view and choosing a method from the interpolation method heading”

Underneath this text is an image showing a "Hips" bone in the PWS. The bone has been selected and has three pull down menus, marked "Transform.Translate X*", "Transform.Translate Y*" and "Transform.Translate Z*". Text under the image reads "The three icons indicated here are actually pull-down menus that give access to a channel's interpolation and extrapolation methods"

OK, wow, where to start here…

Let’s start with what I understand. I pretty much get what the different interpolation (and extrapolation, for that matter) methods are supposed to do, and I understand the last part of the paragraph - In fact the ONLY WAY I see how to apply these different methods is by doing so in the Channel view of the timeline, by selecting individual points or groups of points and bringing up the contextual menu.

As for the rest of it:

1. The names, “translate X”, “translate Y” and “translate Z” (my own version also has a “translate W”, and some other bones/channels have additional letters not mentioned). I understand what the X,Y, and Z axis are but don’t see how that relates to anything that is being discussed here. Are these adding interpolation and extrapolation methods to actions that only happen along certain axis’ (just what is the “w” axis, then?), if so, I can grasp that, but why the statement “center is for the interpolation of the channel in question”. The center? The Y axis? Why does that and that alone translate everything that happens to the bone? Are these in fact the “three pull down menus” being referred to? The image certainly would seem to suggest that.

2. “There are actually three pull-down menus located under that image, the first and last of which look ghosted out and are for extrapolation methods”. No, actually, they’re not. They aren’t even in the image used for illustration, unless I’m looking at the wrong thing, which I kind of suspect that I am.

3. When I click on any of these “translate whatever” pull down menus, I only seem to get different options when I click on the curvy shape - which allows me to chose different sorts of shapes, but I see nowhere to chose different interpolation or extrapolation methods. For that matter, those options that I DO see are explained nowhere in the text.

OK, I think that covers my quandary here. Thanks to anyone who can make this clearer.

 

- Mike

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I do not have much time right now, but just as a headsup for the pre- and post-interpolation stuff:
You can do it for one axis only and stuff like that but you do not have to.
Just click on the "Bones" folder and then select everything by pressing "CTRL + A". Now right-click on the selection and choose the pre- or post-interpolation you want to have there.

In general I do not use it very often... in general I just repeat the action itself not in the action itself, but yes you can of cause do it.

Best regards
*Fuchur*

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On 10/18/2020 at 1:27 PM, Kaijubait said:

 In fact the ONLY WAY I see how to apply these different methods is by doing so in the Channel view of the timeline, by selecting individual points or groups of points and bringing up the contextual menu.

 

If you drill down far enough to expose single channels in the PWS, a small symbol of a "curve" becomes visible that is really three drop-down lists.

image.png

 

The middle one sets the default interpolation for the channel and has itsy-bitsy icons representing the behavior of the four choices...

image.png

 

The first and last drop-downs contain choices for pre- and post- extrapolation, again with icons representing the behaviors.

 

image.png


 

Quote

 

As for the rest of it:

1. The names, “translate X”, “translate Y” and “translate Z” (my own version also has a “translate W”, and some other bones/channels have additional letters not mentioned). I understand what the X,Y, and Z axis are but don’t see how that relates to anything that is being discussed here. Are these adding interpolation and extrapolation methods to actions that only happen along certain axis’ (just what is the “w” axis, then?)

 

 

By default, A:M uses "quaternion" representation/interpolation of bone rotations. Among other advantages it never creates the "gimbal lock" which plagues other systems.

However, it does invoke the mysterious "W" channel which is not intuitive to edit. For most small edits that character animators might do in the curve editor, the W channel can be ignored.

As an exercise, keyframe a bone at 1:00 to rotate one complete 360° rotation from from where it was at 0:00 and play it back. Nothing will happen!

Quat always picks the shortest path between two bone rotations, regardless of the internal numerical representation.

However if you keyframe the bone in successive one-third rotations it will indeed animate in a full turn. If you want to be really weirded out, look at the curves after you have done this. :D

I've never read a comprehensible explanation of Quaternion representation, but by eliminating gimbal lock it greatly simplifies the 3D animator's task.

"W" is rarely an impediment since Characters almost never need to rotate a bone as much as even a half a rotation at a time, but for mechanical animations that do, Euler or Vector interpolation can be opted for instead.

Quote

 

2. “There are actually three pull-down menus located under that image, the first and last of which look ghosted out and are for extrapolation methods”. No, actually, they’re not. They aren’t even in the image used for illustration, unless I’m looking at the wrong thing, which I kind of suspect that I am.

3. When I click on any of these “translate whatever” pull down menus, I only seem to get different options when I click on the curvy shape - which allows me to chose different sorts of shapes, but I see nowhere to chose different interpolation or extrapolation methods. For that matter, those options that I DO see are explained nowhere in the text.

 

 

I'd have to see more clearly what you are doing to understand your question better. Posting a screen cap would be clarifying.

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Your post was a huge help Robcat. The book did not explain this well AT ALL. Part of the confusion is in both the way they explained it and the illustration (which did not show the appropriate drop downs) but I'd also have to say a failure on A:M's part to label what these drop downs are rather rather just using cryptic symbols. At the very least I think the name of the interpolation/extrapolation method should come up when you hover your mouse over the icon.

The only thing I'm still not that clear on is "translate W", but I seem to be hearing that's mostly a superfluous item so I'm not going to worry about it.

As for attaching screenshots. Well, I wanted to, but it only seems that I can attach images that are already uploaded to webspace. I tried uploading a scan of the book with the text that was confusing me to flickr, but when I entered the URL, the site didn't like it. I see now an option to drag or attach files, but I didn't see that when I created the topic, only something that called for web links.

Just for the heck of it, I'm going to attach the text that was confusing me now.
 

anmation_master_book.jpg

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I've never seen a "Translate.W"

Can you show a PRJ that has one?

 

As a person who used to be a teacher and still dabbles in instructional media, what i would say in David Rogers' defense is that it is hard to get the trade-off between clarity and conciseness right for every student.

I look at that picture and see three icons, but maybe not everyone will.

A:M is a full-featured 3D animation program fully capable of professional workflows and results. That means there is a lot to know and explaining it all in one book may be hopeless.  https://brilliantisland.com/images/sisyphus.gif

So we have the forum, where you can ask follow up questions and know-it-alls like me will try to answer. :D

 

 

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but I'd also have to say a failure on A:M's part to label what these drop downs are rather rather just using cryptic symbols. At the very least I think the name of the interpolation/extrapolation method should come up when you hover your mouse over the icon.

They do.

Make sure you have View>Toolbars>Show Tooltips checked

image.png

image.png

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