How to connect objects like this?

Hi there - I'm trying to figure out how to connect objects to create a moving elastic/spider-web-like motion as seen in the following video:
vimeo.com/28135438 (starting at 0:04) wherein the "web" lines are following a motion-tracked point on the spider. I can make the center object (circle) that tracks the video; I can make a bunch of lines that connect to it (web), but I cant figure out how to make the lines stretch and retract from a fixed point like the web in the video. Can anyone help me figure out how to pull this off in motion (without keyframing each transform value, that is)?

I could easily be very wrong here, but I believe there may be a specific behavior for that. That's the only way I would see Motion being able to handle something like that.

It looks like the spider is being motion tracked and a line layer is anchored at the fixed point from where it begins to the spider itself. Being unable to open up Motion at the moment, I can't exactly give you a surefire method of how to do that. Best of luck.

I think it was made with an AfterEffects plugin called Plexus.

Darn - thanks guys. I figured it was AE + some plugin (like Plexus), but I was hoping Motion could pull off a similar behavior without having to keyframe.

I've done that in Motion with tracking, super easy.

Okay, but how to do you apply motion tracking to just one end of a line while the other is locked in place?

In Motion, set the Anchor Point to the static end of the line.
For the moving end of your line, apply:
Behaviors > Shape > Track Points
Mega easy...

He can do camera projection in Motion, too! Mega easy. :lol:

No idea why you would want to move your anchor point, but you can simply draw your line(s), apply the "Track Points" behavior without any anchor point moving, analyze for the needed motion and "attach to source". But if you want to connect more than one point then I'd use the "Analyze Motion" on the moving layer first to extract the tracking data and use THAT as the source for ALL points. That way you're only analyzing once and not once for every layer/point.

The anchor point for lines is the center by default. Tracking will move them from the anchor point. Thus you have to move the anchor point to the end of the line shape. Then the tracker will effect the opposite end. Otherwise it rotates around the center.

I have a free tutorial about how to do this exact same effect coming out at macProVideo.com/hub in the next few weeks. My tutorials there are on really long delays, just the nature of publishing companies. I write something today, it goes live in six months. But hoping this one gets out really soon.

You can do the procedure as described without moving a single anchor point.

How?

Andie, what's going on? Seems like you only joined this forum to question or bash Bens advice. Any special reason for that? It was the same in the only other thread I ever saw you answer to?

I merely call people on their false statements, regardless of who they are. If you want to make one I can take you into my repertoire also... If you feel you see a certain pattern in that, that may give you reason to think...
But I'm not sure which part of "do the procedure as described" is confusing. Simply try it and see if I'm so off base. Because I'm not. I've done it many times over.

I'll answer my own question, then.

There are two techniques.

One is that when using the "Track Points" shape behavior, you are given tracking targets for each Control Point of the shape. Be sure they're set properly, when the Source is a Motion Analyze behavior, and you don't have to change the Anchor Point of the shape.

Two valid techniques, neither is a false statement, they both work fine, everyone play nice.

Okay... "faulty" claim. Since by your own admission moving the anchor point is not necessary (in either cases btw), yes. And that was the answer I gave you before you asked the question, correct.

When you apply the Track Points behavior, by default, the points are assigned tracking points the OPPOSITE of the direction we naturally draw a line of this type. As it is natural to draw from the furthest point, to the point nearest the target. In my classes I have see dozens and dozens of students to this for many, many years now.

Thus when you apply it, you have a choice.
A- Swap out the tracking point assignments in the Track Points behavior.
B- Move the line's anchor point.

Either is valid, both achieve the exact same behavior, no "faulty" claim was ever made.

Best of luck.

No idea what you're doing, but I simply apply the behavior to my "naturally drawn line" (whatever that is), set the points to where they need to track, analyze, done. I can't think of any reason why I would want or need to mess with the anchor point of all things at any point along the way...