Sweeps a grid across the whole sky and checks whether each point clears the walls, the parked roof, and your local horizon — not a dome shutter, since a roll-off roof either fully opens or fully closes.
The whole assembly is rigid and rotates about the mount's pivot — so each telescope's farthest point stays a fixed distance from that pivot no matter which way it's pointed. Plan view (looking straight down): the building outline to scale, with one circle per telescope at its actual swing radius against the walls, floor, and ceiling. Circles are spread apart by each telescope's lateral position on the mount so they're readable as separate telescopes, rather than stacked on one exact point — the radius (not the exact placement shown) is what the wall-clearance check actually uses. A separate check below catches telescopes hitting each other, which wall clearance alone can't.
Measured from the building's true geometric center on the floor (not magnetic north). Positive North offset means the mount is closer to the North wall.
Most buildings are a simple rectangle — the width/length above cover that. Non-rectangular buildings (angled corners, an extension, an irregular footprint) can be described directly as up to 6 walls, each its own distance and angle from center.
The roof rolls off past one wall and parks there — that parked structure is its own obstruction, not just an open gap.
Mount type changes the OTA's swing in the 3D preview and how pier side affects it. Doesn't change the wall/roof obstruction math itself — that's driven purely by true Alt/Az.
Telescope 1 uses the OTA length/aperture and GEM Axis / Dec Offset entered above. Enable up to 3 more for additional scopes riding along (guide scope, wide-field rig, etc.) — each with its own offset along the main axis and lateral offset to the side, for both wall clearance and scope-to-scope clearance. See the Swing Clearance panel at the bottom of the page.
Drag to orbit, scroll to zoom.
Terrain beyond the building — trees, other structures. Layered on top of the wall/roof obstruction; whichever blocks more at a given azimuth wins.
Drives the live obstruction calculation and the 3D preview.