RFC - Project / Unproject Improvements

• Author: Ib Green
• Date: August, 2018
• Status: Conceptual Draft

References:

• View Class Extensions RFC for deck.gl v6.1.
• View Class RFC for deck.gl v5.2.
• Multi Viewport RFC for deck.gl v5.
• First Person Geospatial Viewport RFC for deck.gl v5.
• Infovis Viewport RFC for deck.gl v4.

Summary

This RFC is intended to propose an enhanced project/unproject functionality for API for deck.gl that can handle the many considerations arising from advance features that have been introduced into deck.gl over time.

Considerations

This is a partial list of considerations that should inform the design of a new project/unproject API for deck.gl

Multiple Views

Picking already renders all viewports, so an object can be picked in any viewport. But pick info is not fully updated.

• Should the pickInfo object contain a view descriptor reference?
• Should relative coordinates be resolved within viewports?
• Ability to restrict picking to certain viewport?

Multiple Coordinate Systems

Now each layer can have its own coordinate system. Either LNGLAT or METER_OFFSETS, and every METER_OFFSETS layer can have its own center point and model matrix (the latter should also be true for LNGLAT).

Does it make sense to have a Deck level project/unproject function?

• Should it return values in all coordinate systems?
• Should it traverse the layer list to extract a list of coordinate systems?
• Or should there be an API to unproject towards a specific layer Id?

Custom Coordinate Systems

There is even the idea of supporting completely different, installable projections. Presumably these will be able to expose project/unproject functions to JS.

Can those "installable" functions be integrated into a generic project/unproject system.

Adjustable Ante-Meridian

Shaders are now able to dynamically adjust the "placement" of the ante-meridian, should JS functions also do this to ensure shader and JS rendered calculations and rendering always align?

Can layers use different ante-meridians? Does it matter, since we already have to deal with different coordinate system.

Model matrix inversion

A lot of model matrices, not exactly cheap to calculate inverted matrices? On demand?