Camera Interface for Ufe

[williamkrick]

We're investigating adding Ufe::Camera to support communication of camera parameters (focal length, aperture, etc) from USD into Maya.

The addition of Ufe::Camera & its parameters raises an issue for Ufe that hasn't had much attention: units. Until now all Ufe interfaces such as Transform3d have worked in scene units, which is a behavior which matches how transforms work in most DCC apps.

Camera parameters are a little different. In Maya (and FBX) the camera parameters all have specific units which are independent of Maya's working units. Maya's camera has parameters expressed as inches, centimeters or millimeters, and the Attribute Editor for Maya cameras is similar, expressing values with their own unit type vs. expressing the parameters in working units.

USD is a little different. GfCamera expresses its parameters in either scene units or tenths of scene units.

Our current plan is for Ufe::Camera parameters to use fixed units like Maya rather than varying units like USD. Each Ufe::Camera parameter will use the same unit that the Maya camera uses for that parameter, meaning the Ufe::Camera parameters will be a mix of inches, centimeters and millimeters.

Does using fixed units (inches, centimeters, millimeters) introduce limitations on your workflows?

With this implementation the USD plugin to Ufe in MayaUSD will be responsible for converting from USD scene units into the fixed units that Ufe is expected to provide.