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Unkinking IK

Author: 3Don


Sometimes Inverse Kinematics can surprise you with odd results when working in Poser. Here are some common kinks and what to do to fix them.

Step 1 - Flip Out


Have you ever applied a hand pose to a figure and then see the body suddenly flip out? The body looks like the result of a judo flip. Inverse Kinematics (IK) is the cause.

Most likely the hand pose was saved to a Library with IK turned ON for that hand. Applying such a pose, with your own IK on or off, will distort the figure.

It depends on the combination of IK settings which were ON for the original body who's hand was posed, as to how to remedy this. Which IK settings were ON cannot be determined for an imported pose.

First, try to Undo the application of the hand pose. If that works, dump the pose from the Library and find or make another. Never save hand poses with IK turned ON.

Sometimes, undo won't undo….

Next, try this. Be sure IK is OFF for every limb of your figure. Reset all Twist, Bend, and Side-to-Side Parameter Dial (PDs) settings to zero for the hand which caused the distortion. It should appear normal, without mesh warping. Then set all Body Rotation PDs to zero.

At this point the figure and hand should appear almost as it was. The body or hips may need some rotation adjustment to be set right.

If this latter method works, re-save the hand pose over the distorting one.

In the image “Hand Flip” you see a right hand pose (saved with IK on) applied, flipping the body.

Step 2 - Bad hands to glad hands


Have you ever turned IK on to fine-tune hand placement and then, when IK is turned off for that hand, it appears distorted? What has happened is the placement of the hand, though it is in a natural position, has distorted the collar-shoulder-forearm relations to that hand. It is actually those body parts which distort. That hand, at the end of that chain, only shows the distortion. You may notice that all of the Twist, Bend, and Side-to-Side PDs have much higher numerical values, and different than before IK was turned OFF.

Turn OFF IK, and reset all Twist, Bend, and Side-to-Side Parameter Dial (PDs) to zero. The hand will look normal again, but not quite in place as it was. Most of the time you only have to tweak the Bend PD to reposition that hand. You may have just a little tweaking to do with the other dials to get it all right.

The “Hand Twists” image shows a hand that was posed then moved with IK on. When moved, the distortion starts to happen, seen on the left. When IK is turned off, the hand appears as in the middle image. When hand PDs are re-zeroed and the hand is then bent a little, it appears as the image on the right.

Step 3 - Good hands and sore shoulders

Sometimes using IK to place a hand does not result in extreme distortion. However, the collar-shoulder-forearm looks un-natural. Leave IK ON for that hand. First, select the collar and try adjusting its placement to see if it will look more natural and smooth out the hand mesh. The hand will remain in place as the collar moves. It may take a little experimenting to do this. You may get closer to a natural look, but maybe not quite.

Then try the same thing with that hand's shoulder. It should get you closer. The collar will move most with IK on for a hand. The shoulder will move less, and the forearm practically, not at all.

Step 4 - On Bended Knees

Have you ever tried to lower the hips of a figure with IK turned ON to lower the body and bend the knees and have the result look like it is extremely knock-kneed? Straighten things out this way.

Before lowering the hip with IK on, save the pose in the Pose Dots area for quick re-application of the original pose if needed.

IK works about the same for the legs as it does the hands. Adjusting the buttocks-thigh-shin chain is similar. Moviing the buttocks results in some movement, the thigh results in the most, and the shin almost not at all.

First, try moving a thigh left or right to see if the leg starts to look more natural. Or, try the twist or bend dials. If one does not seem to work, Undo and try another. What works depends on the placement settings of the hip, which can vary greatly in poses.

If the first method does not seem to bring the results expected, select one of the feet and with the Trans PD move the foot in whatever direction looks logical (in your pose) to see how it affects the knocked-knees.

Sometimes using some of both methods is necessary.

Step 5 - Bent Outa Shape?


This is one that I thnk has happened to all of us. You move a figure by the Hips (rather than the body) and the hand(s) or feet stay in place, distorting the figure. IK was ON for whichever body part did not move. Undo, if you'released the mouse button. Or, re-apply the original pose, to get your figure back to where it was. Turn IK OFF. Move the figure.

You can move a figure with IK turned ON if you select the Body and move that, rather than the hips.

In the image “IK Hip Movement” you see where IK was on for the left hand and right foot when the hips were moved. The arm goes through the head and the foot keeps its X and Z positions, but raises along the Y axis.

Step 6 - Coddling IK

Inverse Kinematics is a wonderful tool to use. It can be pretty finicky sometimes. I constantly turn it on and off for different limbs as I pose figures. Generally I use IK only to fine tune hand and leg movement. I DO NOT use IK to bend, twist, and side-to-side the hands or feet.

To understand why, try this.

Load a figure and a pose. Use a pose where the hands are somewhat bent, twisted, and/or moved side-to-side. Be sure IK is OFF to start with. Select a hand and take note of the Parameter Dial settings.For instance, say the hand is bent +10 degrees, twisted +5 degrees, and moved to the side -12 degrees. Now turn ON IK. Note again the PD settings for that hand. All have changed value. Usually the number values are much higher. It could now read =160, +20, and -45. I do not know why that is, but it happens.

So, try bending that hand with IK on in a logical direction. Often what seems right, is not. The hand will go the wrong way, or appear to twist instead of bend. Poser must assign some other value ratio to the hand placement with IK on.

Another odd thing about IK is that when a hand or hoof is moved with IK, parts of the hand or hoof can become somewhat distorted. What happens is that IK can alter settings for the fingers or parts of an animals legs.For instance, moving a hand can bend or twist some finger joints away from where they were set. The hand may not look too far off, but enough to look strange. After you have used IK to position a hand jor animal hoof, check the finger settings to be sure no 2nd or 3rd joints are moved side-to-side or twisted. If they are reset them to zero. These parts of the fingers do not move this way, (unless broken!) even though Poser has settings for them to do so.

To save time and aggravation, only use IK to move the hands. If you need to tweak it a little with a bend or twist, turn OFF IK and bend or twist. Turn it back ON to move again.

Once the hand pose is right, turn OFF IK and save the hand pose to the Library.

IK is tricky, but manageable. Knowing when and how to use it will enhance your posing skills and allow you to work faster.

See my Tutorial on this site about placing props in hands and using shadows to guide you.