Motion Path weirdness

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Old 12 December 2005   #1
Talking Motion Path weirdness

Hi Guys have a problem with what i assume is my motion path. Basically the problem is;

I have createrd a motion path and have attached my character to this all correctly and it moves along it great apart from one minor problem. When My character gets a few frames in his orientation changes and he rotates 180 degrees, This stays this untill the last few frames where this changes back so he is the right way.

Basically what i have done is tested it on a straight motion path and this is fine but when i make the path curved of any sorts it has this problem. Incase it makes any difference my character is moving verticaly like a helicopter.


Last edited by galeru : 12 December 2005 at 03:25 PM.
Old 12 December 2005   #2
You have to setup the correct front/up-axis values in the motionPath node. For example, when using a simple cone, set front to Y and up to Z to make it travel along the path in a rocketlike fashion.

Of course these settings depend on the design of your character and path. You might also consider using a different World Up Type.
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Old 12 December 2005   #3
i have it working thats not the problem the problem is that after about 12 frames it suddenly turns the oppositye direction and then 12 about 15 frames before the end it turns back apart from this i everything is fine.

so basically i see the characters face and then suddenly he does a 180 degree turn and then at about 36 frames he turns back the right way again

any ideas??

Old 12 December 2005   #4
No ideas. Sure you didn't accidentally key the transformations? :P
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Old 12 December 2005   #5
I know exactly what you're talking about... pretty freaking frustrating. Here's what you could do...
go to the first frame in your timeline where your character starts flippin' out on you, select your curves and haves the CV's visible. Grab a CV and start moving it around. The reason (as far as I know) that your character is changing directions like that is because the CV's aren't in a "clean" position and therefor the curve is interpolating the tangents in a funky manner.
Hopefully that gives you a start to fixing it.
Old 12 December 2005   #6
Had the same problem. Here's how to fix. Using your original path extrude a nurbs surface along it so you bascially have a ribbon like plane following the direction of path. Delete the original curve. You might be able to see the problem areas in the surface, if not no worries. If you do see problems smooth them out to your liking. Now make the surface live. Using the EP curve tool make a curve down the center of the surface by curve constrain clicking once at each end of the surface. You should have a curve similar to your original. Now make the surface not live and hide the surface. Attach your character to the path with "World up" type set to "normal". This will make sure your character will orient to the surface's original normals and eliminate random rotating. You will still have to set your front axis and up axis to suit your needs. I had a project where i had a camera following a long windy path and this is how i fixed.
Old 12 December 2005   #7
Quote: extrude a nurbs surface along it so you bascially have a ribbon like plane following the direction [...]
Well, this sounds like unnecessary hassle to me. Usually rebuilding the curve should suffice. This way you are given a lot of control about how the components of the curve will be distributed.
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Old 12 December 2005   #8
Originally Posted by lowkey: Well, this sounds like unnecessary hassle to me.
It is absolutely necessary and that’s the only way to prevent a camera from flipping on a motion path that has loops in more than one dimension.
You can make such path by just drawing a curve with a complete circular loop in one orthographic view and then finish the curve in another orthographic view by drawing another loop there. Now it is very easy to imagine how the camera will flip at one point or another when you apply any of the orientation options available for the World up Type.

At first look the most useless option is the Normal type. Maya doesn’t display curve normals like it does for polys and nurbs surfaces but you can easily visualize it by imagining the line that connects each EP to its corresponding CV, which in other words means the camera will travel along the curve and at the same time keeps its orientation towards the hull. This will result in a camera flipping all the time on every turn of the curve. You can visualize this by just drawing a simple S curve and displaying its hull which will reveal how the hull crosses the curve on every turn.

The trick to avoid the flipping is not so obvious until you read the online help for the Normal option. They say that if you use a curve on surface instead of a curve in the world space, Maya will use the normals of the surface for the orientation of the camera. This now not only gives a option to avoid the flipping but building a nurbs ribbon for the curve also gives a very intuitive way of controlling the orientation of the camera.

Hope this helps

Last edited by Emil3d : 12 December 2005 at 04:39 PM.
Old 12 December 2005   #9
Aha, now that's very interesting indeed. Thanks for clearing things up!
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Old 12 December 2005   #10
Oh and Just for the record. Emil I believe you were the one to show me this fix a few months ago. So thanks again.
Old 12 December 2005   #11
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