# Constraints In Action

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Constraints | Constraints in Action

Constraints at their most basic are controllers, controlling how one item relates to another. Constraints can serve many purposes, and when used in combination with each other can create very complex controllers and motions. Rich explains, by example, each and every one of modo's available constraints, providing an in-depth look at the fundamentals of automation in the rigging process. The 'Constrains' page goes over the constraints themselves, while the 'Constraints in Action' page shows some actual usage scenarios of constraints (selected above).

Users can jump ahead to a specific section by using the Chapter selection widget on the right side of the player or by directly clicking any of the Chapter Title links below.

Tab | Time | Chapter | Description
1 | 0:00:44 | Wheel Example | Demonstration of constraints used for a rolling wheel.
2 | 0:19:26 | Normal Example | Demonstration of constraints used to attach an object to a point aligned to its normal.
3 | 0:41:03 | Turret Example | Demonstration of constraints used to control a gun turret assigned to a curved path.
| 1:11:29 | Total Video Time |

Frequently Asked Questions--

Q.) I see that some of the locators have description text displayed in the 3D view, how is that done?

> A.) In the Display properties for that locator there is an option called "Label" just fill that in and a label will show up. Check out the Locator Mesh Display section for more information.

Q.) Wait, he said that you shouldn't plan for EVERY possibility when building a rig?

> A.) YES! This is a big trap new riggers fall into, trying to make an "unbreakable" rig. Not only is that task impossible, it forces you to spend more time on a problem than is required. This does not mean you should not make your rigs robust, just that seeing it in context, using common sense and talking to you client is important when decided how much it too much.

Q.) "Remove Channel From Assembly"? I thought he was working in the Schematic view?

> A.) In modo, the Schematic 'Workspace' is really just a special Assembly Group, so when you are adding and removing things you actually are working in an Assembly. Check out both the Schematic and Assembly Groups section for more info.

Q.) Isn't it spelled "Axle" and not "Axel"?

> A.) Shh! Rich can't spell, but he knows his rigging... so let him teach.

Q.) When moving an item sometimes he grabs one of the circles instead of the handles, what are they for?

> A.) Those allow you to move an item in just the "plane" of an axis... so in the case of the red circle it would only move in the YZ plane. Its just short hand to help you move something flat.

Q.) When he connected the locators to the sphere's vertex's they look like they are floating in front of the geometry and not actually on it, why?

> A.) That is because the sphere is a "SubDivision Surface" (or subdiv) and the vertices constraints connect to the "cage" point that defines the subdiv, not the limit surface (the smoothed one).

Q.) Sometimes the scene's basic channels show up in the properties and channel editors, why?

> A.) When you click on a scene's name to jump to it in the item list you are in essence "selecting" the scene item (yes, even the scene is technically an 'item' in modo). To remove these channels just 'Ctrl' click on the scene to deselect the scene item's channels.

Q.) Wait! You told us to never offset a rotation in a constraint by more than 90 degrees, and you used 180 degrees?

> A.) Yes. Yes he did, and like all things in life there are always exceptions to every rule. In this case, since the scope of what needed to happen was limited, over rotating that offset was not going to be a problem. The lesson here is to judge how quickly you can achieve a rigging result against possible complications down the line. So for instance, If he needed to gang more constraints on top of this items rotation he might have changed his approach but since he didn't, he was able to make a quick fix to solve the problem at hand.

Q.) He clicked on the cyan cylinder around the turret's base and the channel haul tool just popped up, how did he do that?

> A.) Using the "item.channelHaul" command in the assembly tab... head over to the Assemblies and Rigging UI section in the training to learn how to use that and other nifty controls.

Q.) You can have more than one "Position" on an item?

> A.) Yes, you can have as many as you would like. This one of the most powerful tools in modo's rigging toolbox. Check out the Transform Items section in the training to learn more.

Q.) He keeps talking about a channel being a "float" what does that mean?

> A.) A "Float" means a Floating Point number... or simply put any number that has a decimal place. So a value of 1.004 could have its decimal point moved to change its value to 10.04. Its decimal point can 'float' to different positions in the number to change its value. See the Channels section for more information.

Q.) Why is "World Position" a matrix4 and not a collection of XYZ position channels?

> A.) Modo stores an items "World Transformation" as a matrix4, the "World Position" then just extracts the XYZ coordinate that it needs and passes it on as a "filtered" matrix4. Internally it's storing the accumulation of any transform items or constraints' input that are affecting it. There is not always an easy way to extract these values as XYZ channels (especially in rotations case). Also to be honest, it's just the way Luxology intended to handle these kinds of tools and problems.

Q.) He keeps mentioning a "Matrix4D" channel but I only see a "Matrix4" what's the difference?

> A.) There is none. Matrix4 and Martix4D are just terms for a 4x4 matrix. So just ignore him when he adds that silly "D" at the end. If you want to learn a bit more about what a matrix is, check out the Channels section.

Resources--

Links to the modo in-line help system
Docs: Locator Display Options
Docs: Constraints
Docs: Schematic

Links to other pages in this training
Training: Locator Mesh Display
Training: Constraints
Training: Schematic
Training: Assembly Groups
Training: Assemblies and RiggingUI
Training: Transform Items

Files--

Links to the modo scenes used in the video
(click to open in modo)
File: ConstraintsInAction_01a.lxo
File: ConstraintsInAction_01b.lxo
File: ConstraintsInAction_02a.lxo
File: ConstraintsInAction_02b.lxo
File: ConstraintsInAction_03a.lxo
File: ConstraintsInAction_03b.lxo

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