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ISM: I am busy with a round-tripping process between ISM and Strand7. Would you please explain how the orientation axis t is derived?

Trevor Dunn
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As I understand via section 11.3 of the ISM API 6.0, the R-axis is defined by the member location and would be the unit vector between the start and end nodes of the member. I do not see further information like this regarding the orientation axis t, but do see it under the orientation heading within the structural synchronizer of the ISM repository. Would you please explain how the orientation axis t is derived?

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    Here's some content from the help. 

    Coordinate System

    The coordinate system for a curve member is as follows:

    • R-Axis: Along the member from start to end along Location
    • S-Axis: Defined by R- and T- axes, such that R x S = T (right-hand rule); (for horizontal beams this is typically a horizontal vector)
    • T-Axis: Defined by Orientation property (for horizontal beams, this is typically vertical)
    The unit vector orientation of the member T-axis For curved (or kinked) curve members the orientation is modified along the member length by the "Parallel Transform Approach". The modification is the obvious correct modification for curves in a plane and is a reasonable modification for truly 3 dimensional curves.
    The programmer's guide has a picture. 



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    Hi Seth, Thank you for your response.

    I understand how the T-axis is defined, but would like to possibly rephrase my question:

    Our workflow is from Aecosim Building Designer <-> ISM <-> Strand7, where the arrows represent a back and forth workflow.

    I am struggling with the local orientation of the members within the strand7 model, but am aware of how strand7 implements local axis orientation. What I feel I am lacking is an understanding of how the T-axis is defined and transferred from Aecosim to ISM. Is it based on the geometry of the section, and if so, how? Is there vector algebra involved? I can see the T-axis, orientation vector in the structural synchronizer but would like to know how this vector is calculated.

    Any help would be appreciated!

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