Problem solving ceiling geometry

Grainchek in the office: When I’m working from home I use Grainchek similar to when I’m in the field. The day starts with pressing the big green “START” button. Then I use task camera icons to take photos of my computer work at different stages in the process. Finally I use feeds to share, collect and quantify the time spent. Now I need to find the radius of the ceiling at a given location, with a given ceiling pitch and given ceiling height. c=1/2e