All online tools use javascript to calculate the dimensions. Use at your own risk. If the answers look wrong then verify the answers with a calculator.

What is a Polygon?
A closed plane figure made up of several line segments that are joined together. The sides do not cross each other. Exactly two sides meet at every vertex.

What is a Bay Window Polygon?
Four walls that are joined together. The four sides of the Bay Window do not cross each other. Exactly two sides meet at every vertex. There are a least two Bay Window walls parallel to each other.

What is a Bay Window?
Bay window: A composite of three or more windows, usually made up of a large center unit and two flanking units at 30°, 45° or 90° angles to the wall.
Canted: with a straight front and angled sides.
Any window space projecting outward from the walls of a building. The bay must be square or polygonal in plan.

This bay window rafter script - calculator is based on the straight skeleton of a polygon with the bay hip rafters bisecting the bay window projection walls corner vertices. When the bay hip rafters bisect the corner vertices the rafter pitch is the same for both the face wall and the angled projection wall.

The script will return the bay window geometry angles and trigonometry rafter measurements for all types of equal pitch bay window roof framing. The script is not limited to 45° bay windows calculations. The bay window side projection walls can be at any angle between 0° - 90°.

 

Constructing roof geometry for complex polygons : Straight Skeletons straight skeleton of a polygon

baywindow.dxf -- auto generated DXF CAD file of baywindow drawing each time script is run
baywindow.pl source code for perl script that generates these baywindow calculations
dxf_header.txt DXF header text file used by this script