Physical Cameras for USD

[meshula]

Physical Cameras for USD

On behalf of the Cameras in USD Working Group:

This schema usefully bridges the description of physical cameras to USD scenes.

rendered link:

https://github.com/usd-wg/OpenUSD-proposals/blob/physical-camera/proposals/physical-cameras/README.md

The physical camera is a primitive meant to be a target for construction of
a physical camera model through applied, and multiply applied schemas.

The physical camera is a GeomXformable, and thus inherits the transform
schema.  The physical camera also inherits the UsdGeomImageable schema,
which provides facilities for controlling visibility and rendering of the
camera.

The physical camera provides a number of attributes that are meant to be
authored by a user or by a DCC import process.  These attributes are
generally meant to be authored once, and then left alone.

The concept is that the PhysicalCamera is just like a real camera that may
be used and measure on a real life stage, and it's attributes recorded in
a usd file. A real camera is a body, with a lens, and a film back, all
interchangeable, and these concepts are reflected in the proposed schema.

Supporting Materials

n/a

Contributing

• I agree to and accept the Supplemental Terms.

[dennis-lynch-nv]

Why a float type for this value?

[meshula]

That follows GfMatrix where we see

    /// Returns the sign of the determinant of the matrix, i.e. 1 for a
    /// right-handed matrix, -1 for a left-handed matrix, and 0 for a
    /// singular matrix.
    GF_API
    double GetHandedness() const;

    /// Returns true if the vectors in the matrix form a right-handed
    /// coordinate system.
    bool IsRightHanded() const {
        return GetHandedness() == 1.0;
    }

    /// Returns true if the vectors in matrix form a left-handed
    /// coordinate system.
    bool IsLeftHanded() const {
        return GetHandedness() == -1.0;
    }

we find code like this throughout OpenUSD:

        // negate the angles
        *thetaSw *= -handedness;
        *thetaFB *= -handedness;
        *thetaTw *= -handedness;

usd files have it as a token

        uniform token orientation = "leftHanded" (
            hidden = true
        )

I agree that instead of a handedness float, we should match the orientation token usage.

[dgovil]

Link to Rendered Proposal for convenience