The Joint Parameters

Joint parameters control how the body parts adjacent to a joint are deformed when we move the joint. For example, if we bend the knee, part of the thigh and part of the shin will be deform. Most of the thigh should not move at all, most of the shin should make the full movement. In between, at the knee, should be a zone of transition between the two. This is the zone of deformation, because in this region the shape of the body parts is altered by the joint.

To edit the joint parameters I open the joint editor and select a body part. I usually work from the hips outward, but that is a matter of taste. Each body part controls the joint to its parent, e.g. the shin controls the knee joint.

The poser manual chapters about the joint editor are a good introduction; you should read them in detail before working wit this tool.

It is easier to see the joint parameter in the outline mode, but the shaded mode is better to control the deformations, so I switch the display mode often. It can also be useful to swizch between the main camera and the orthogonal (front, left, right, back, top and bottom) ones.

The first thing to do for each joint, is to set the joint order (or rotation order). The first axis should be twist axis, the one that follows the main axis of the body part. The last axis should be the most important rotation axis for the joint, the remaining one goes in the middle.

For the shin, the twist axis is the y-axis, the most important rotation for the knee is around the x-axis, so the shin rotation order must be yzx. The same is true for the feet, thigh, the buttock, the hip, abdomen, chest, neck and head. The toes use zyx.

The body parts of the arm (collar, shoulder, forearm and hand) are oriented along the x axis, so that will be the first axis. For most of these parts, the most important rotation is up-down (around the z-axis), so the rotation order will be xyz. The forearm is the exception with xzy, because the main rotation is around the y axis. The finger joints use xyz, with he exception of the first thumb joint, that uses zyx.

When the joint order is set, the next step is to set the center point for the joint. This is pivot point for the rotations and it is very important to set it right. I can not give any hard rules how to find the right spot. The only way to get a feeling for it is to study the movement of real limbs (a mirror helps), study setups made by other people and much experimentation.

Now I have to align the axes of the center point with the movement axes of the joint. In most cases, the auto Align button in the joint editor gives a good starting point; I use the sliders to fine tune. After that I try the joint and check that the rotation goes in exactly the right direction.

The dials in the parameter window will be named yRotate, zRotate and xRotate. Now is a good time to change that to better names. To do that, I double click on the parameter dial, and change the name in the dialog.

In the joint editor I change to the twist axis in the drop down menu on the top. This displays the handle bar control. It has a red bar on the parent side and a green bar on the child side. The deformation zone is between these two bars. I adjust the bars localize the deformation where I want it.

In some cases, it is not possible to get good results just with this control, because it can only limit the deformation in one dimension. In these cases, I need to activate the spherical falloff zones. That will display the green inner zone and the red outer zone.

These spheres will limit the deformation zone: Anything that is included in the green inner zone will make the total movement and nothing not included in the red zone will move at all. So the deformation is limited to the geometry in the red and not in the green zone.

The interaction between the zones and the handle bar is a bit confusing: To my best knowledge, geometry included in the red zone but upwards of the red bar will not deform, but geometry in the red zone and downward of the green bar will, unless included in green zone. Geometry in the green zone will do the full movement only if downward of the green bar.

So: With spherical falloff zones, any geometry that is upward of the red bar or not included in the red zone will not move at all. Geometry that is in the green zone and downward of the green bar will do the full movement. All other geometry (in the red zone, downward of the red bar and either upward of the green bar or downward of the green bar and not included in the green zone) will be deformed.

But it gets even more complicated: Only geometry belonging to the body part of the joint and its direct parent can be deformed. Children of the body part will always do the full movement and the parent of the parent as well as all other children of the parent will not move at all.

This has some important implications for the joint setup: To get smooth transitions, the border between the body part and its children must be downward of the green bar, if no spherical falloff zones are used. With spherical falloff zones, the border can be either downward of the green bar and inside the green zone, or upward of the green bar and not included in the red zone.

Borders between the parent and its own parent or other children must be upward of the red bar or not included in the red zone. They must not be in the green zone. If I not follow these rules, it will result in bad deformations at the borders.

To get good results with spherical falloff zones, it is often necessary to scale or rotate the spheres.

The other joint directions (Usually named Bend, UP-Down, Front-Back or Side-Side) will two red and two green lines forming a cross instead of the handle bar. These are the inclusion and exclusion angles. The deformation zone will be between the red and the green lines. Everything between the red lines will not move and everything between the green lines will make the full movement.

If the spherical falloff zones are active, they work the same way as with the handle bar. The same rules for the borders apply.

I sometimes find it necessary to adjust the center point at this stage. If I do that, I usually have to adjust the parameters for the other directions of the joint, too.

The eyes are a special case: I have to make sure that the center point is exactly at the centre of the eyeball. That works best in the wire display mode. The eye movements should not deform the head. I donít know any way to prevent tis from inside of poser. Instead, I open the cr2 file in a text editor, make a backup copy under a different name and search for a line like that:

actor head:1

A bit lower there will be channel entries that look like that:

		twistY rightEye_twisty
			{
			name rightEye_twisty
			initValue 0
			hidden 1
			forceLimits 0
			min -100000
			max 100000
			trackingScale 1
			keys
				{
				static  0
				k  0  0
				}
			interpStyleLocked 0
			algorithm 0
			otherActor rightEye:1
			matrixActor NULL
			center -0.0195846 0.550069 0.0119436
			algorithm 0
			startPt 0.550069
			endPt 0.550413
			flipped
			calcWeights
			}

There should be 6 of these blocks where the otherActor line reads rightEye:1 or leftEye:2 . I delete all that blocks and save the file. When reloaded in Poser, the eyes will work as expected.

That is everything I know about rules for the joint setup, everything else is trail, error and experience.

Sometimes, it becomes clear during joint setup that the borders of the body parts are not ideal. In these cases, I save the figure to the library, go back to my Wings file, change the assignment of the body part materials and reexport the model as described at the end of the previous tutorial.

When the joints are done on one side of the figure, I use the symmetry tool to copy them to the other side.

Now is the time to do some poses to test the setup. I usually need to make adjustments during the creation of a number of poses, before I am satisfied with the joints. An ambient occlusion render is very good to show up bad deformations.

The parameter for scaling body parts can also be set in the joint editor. I have to confess that I usually donít work much with them, so my figures donít scale very well. Therefore, I can not write much about them, maybe sometimes in the future.

In the next installation will be short, just some finishing moves for the poser.