problem in understanding ''Feature Based Panoramic Image Stitching ''

I'm on studying the ''Feature Based Panoramic Image Stitching '' and I have 5 questions

the link: https://www.mathworks.com/help/vision/examples/feature-based-panoramic-image-stitching.html#zmw57dd0e3712

1.how should I fill these 2 lines if my images are in the folder on my pc { buildingDir = fullfile(toolboxdir('vision'), 'visiondata', 'building');

buildingScene = imageDatastore(buildingDir); }

2.why we use eye(3) for projective2d ?

3.in match features, what is the role of 'unique'?

4.in tforms(n).T , what do we mean by <.T> ?

5. what is the role of step and imref2d in this code?

tnx