Crop view?

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Hi all, I'm not sure if this is the place to ask. I have downloaded a sketchup file from vray's website at a tutorial page: https://docs.chaosgroup.com/display/VRAY2SKETCHUP/Rendering+an+Exterior+Scene

In the file, one of the scene appears to have a 'cropped' feature in which the areas outside perhaps a specified rectangle are darkened (changes as I change my window size)

I tried to Google high and low as to see what this feature is but I cannot find anything about this. Anyone can shed some light?

See attached image

[Box]

Go to Tools/Advanced Camera tools and Reset Camera.

[2387581]

Thanks, this is something new to me.