Is there any api for get projection matrix of camera?

Developers Ruby API
1

For other SDK, projection matrix is a property of camera:

How to get it from ruby API of Sketchup？

2

I think SketchUp doesn’t expose its internal projection matrix directly to users or the Ruby API, but you can check Camera properties like FOV, aspect ratio, and perspective/parallel … etc.

You can also check the View class and its methods to manipulate the current point of view of the model. (like e.g. #screen_coords method transforming 3D coordinates into 2D screen coordinates)

You can get camera using the view.camera, so you can manipulate these camera parameters for current view.

3

You can get it using a C Ruby extension via the C API:

SUCameraGetViewTransformation()