ROLL OFF ROOF OBSERVATORY GEOMETRY CALCULATOR
All input dimensions must be in decimal inches. Horizon angles calculate once all required variables are input. Use the up and down arrows for any variable to change its value and the horizon angles will update dynamically. The critical point for calculation is the intersection of the RA and DEC axes and measurements are based on this intersection. It is not the same as the center of the pier in the north-south direction and varies with both mounts and latitudes. You will determine the pier offset manually by measuring at the mount when it is set for your latitude.
The example below shows a square observatory with the RA-DEC intersection centered in both directions. Rectangular observatories and offset mounts are modeled by inputting the various actual distances to walls. If the roof in the open position adds obstruction height above a wall, increase the wall height by the increased obstruction height and note the horizon angle for that wall while ignoring the others.
Angle of North and South Horizon Access is determined when the counter weight bar is horizontal and altitude is just about to put the top of the wall in the FOV.
Angle of East and West Horizon Access is determined with the OTA pointing due East or West.