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Thread: What format are In and Out Tangents in?

  1. #1
    Junior Member
    Join Date
    Aug 2006
    Posts
    4

    What format are In and Out Tangents in?

    Using ColladaMax 1.06:
    I am getting 3 x,y pairs for every point. What values do i want to use as tangents?


    <source id="Box01-node-translation_Box01-node_translation-input">
    <float_array id="Box01-node-translation_Box01-node_translation-input-array" count="3">0 1.000000 2.000000</float_array>
    <technique_common>
    <accessor source="#Box01-node-translation_Box01-node_translation-input-array" count="3" stride="1">
    <param name="TIME" type="float"/>
    </accessor>
    </technique_common>
    </source>

    ...

    <source id="Box01-node-translation_Box01-node_translation-intangents">
    <float_array id="Box01-node-translation_Box01-node_translation-intangents-array" count="18">0.999792 -103.899780 0.999792 -70.887299 0.999792 0 0.666700 7.041927 -0.196099 231.755829 0.666700 0 1.666700 101.453033 1.666700 -63.101410 1.666700 0</float_array>
    <technique_common>
    <accessor source="#Box01-node-translation_Box01-node_translation-intangents-array" count="3" stride="6">
    <param name="X" type="float"/>
    <param name="Y" type="float"/>
    <param name="X" type="float"/>
    <param name="Y" type="float"/>
    <param name="X" type="float"/>
    <param name="Y" type="float"/>
    </accessor>
    </technique_common>
    </source>

    Thanks,
    Mark

  2. #2
    Senior Member
    Join Date
    Jul 2004
    Location
    Santa Clara
    Posts
    356
    Those look like sources of an <animation><sampler> ?
    What does the sampler tell you ?

    Regards

  3. #3
    Junior Member
    Join Date
    Aug 2006
    Posts
    4

    Yes

    They are from the <Animation> and <source> and <sampler>. I'm just trying to figure out why I have 3 sets of X, Y for a single time point.

    Maybe I'm just confuzed by bezier curves...

    Between any two time points I have a Bezier Curve Segment using the 3 given tangents as the 3 parts of the 4 control vertices that represent that curve? But then why would I need 9 total tangents to represent a 3 point curve? Shouldn't I just need a single In tangent XY pair and a single out tangent XY pair for each of the points?

    And since its in 2D how does that flow over to the 3D shape the movement represents?

    Thanks for your help

  4. #4
    Senior Member
    Join Date
    Jan 2006
    Location
    Foster City, CA
    Posts
    540
    Unfortunately Collada animations are in a somewhat confused state right now since they don't match exactly what the DCC apps do. There's a long, boring thread about this issue here. It seems that some DCC apps (Max, Maya) have chosen to start exporting animation curves in the DCC-style instead of the standard piecewise cubic curve format that's described in the Collada book.

    That's one issue. Another issue is that Max stores independent curves for X, Y, and Z translations, but (in some cases) merges them when exporting to Collada. The six values you're looking at for a control point are timeX, valueX, timeY, valueY, timeZ, and valueZ.

    See this for more info.

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