Rendering is driven by a JSON render parameters specification that contains one or more tile specification elements that describe the source images and transformations for the canvas to be rendered. Each tile specification element contains location information for a source image and (optionally) its mask along with zero or more transform specification elements that describe how the source image should be transformed.
Here is an example of a simple render parameters specification:
The render database is a MongoDB document store that supports large scale persistence of tile specification and shared transform specification data. Access to the document store is managed through the render web services. Stored specification collections are grouped by stack as follows:
To reduce the storage footprint, we've introduced an unorthodox relational element to the document data structure. All shared transform specification documents (e.g. lens correction transforms) are stored in a separate collection and can be referenced by id from individual tile specification documents. The render web services handle resolution of the references before returning specifications to clients.
Here is an example of how the relationships are used:
