The Horizon Angle API returns a circular profile of angles to the horizon for a location at a given latitude, longitude point. The angles are calculated based on the surrounding terrain elevation from a 90m horizontal-resolution digital elevation model.

The angle returned is relative to due north, with negative angles eastwards and positive values westward . Varies from -180 to 180. A value of -90 means east, 0 means north, and 90 means west.

No, Solcast retrieves altitude information from our data source and takes this into account. Hence you do not need to provide altitude information for the Solcast Horizon Angle API.

Yes it does account for the height of buildings however the Solcast horizon angles product is designed for far shading / horizon shading and very local effects like a neighbours house won't be included.