* **Authors**: Ravi Akkenapally and Ib Green

* **Date**: August 9, 2017

Notes:

* Please add comments as reviews to the [PR](https://github.com/uber/deck.gl/pull/839)

* **Date**: Aug, 2017

* **Author**: Ib Green

* **Date**: August 10, 2017

References:

* The initial [Infovis Viewport RFC](../v4.0/non-geospatial-viewports-rfc.md) for deck.gl v4.

The map system typically locks in FoV (Field of view), viewing angle (always pitched downward) and altitude (camera height over the “ground”).

When rendering 3D environments on top of pre-rendered video (e.g. overlaying perception data on top of vehicle log cameras)

In deck.gl 4.1 only the WebMercatorViewport can handle layers with geospatial coordinates: it is the only viewport that can produce the uniforms required by the project module. But moving some properties from the `WebMercatorViewport` class into the base viewport, it is possible to extend cartographic projection to all viewpott.

The key insight is that through the addition of the "meters mode", we have already addedthe general capability of overlaying an arbitrary linear coordinate system (which is what all non-geospatial viewports use) on top of a geospatial coordinate system using an anchor point.

While METER_OFFSETS mode was initially introduced to solve a narrow use-case, the technique is actually very general, and there is no reason why we would not support geospatial anchoring and linear coordinates for all viewports (in addition to layers), including first person and orbit (i.e. third person) viewports.

In deck.gl v4.0, a viewport class hierarchy was introduced to support non-geospatial viewports. It separates between `Perspective` and `Orthographic` cameras (inspired by common WebGL frameworks).

Also, since the majority viewports will be used with a perspective projection matrix, if the `projectionMatrix` prop is not supplied, `Viewport` will try to create a perspective projection matrix using new `fov`, `near` and `far` props (note that `aspect` is automatically calculated from `width` and `height`).

New properties:

- `longitude` - (optional) anchor

- `latitude` - (optional) anchor

- `zoom` scale - This will be hardcoded to meter = unity scale by `FirstPersonViewport`

- `far`

New Methods:

* `Viewport.isGeospatial()` can be called to check if a viewport is geospatially "enabled". If longitude, latitude and zoom are supplied to a viewport, then that viewport is considered geospatial.

* `Viewport.isMapSynched()` offers an easy way for the app to determine if a base map can be displayed under the viewport.

* `Viewport.getMercatorParameters()` offers a way to get map props that include offsets etc.

Remarks:

* `modelMatrix` - A convenience to make the viewport API more similar to the `Layer` props. When positioning the camera in a scene with `Layer`s using a certain `modelMatrix` it is nice to be able to use the same coordinates and the same `modelMatrix` with the viewport.

* `projectionMatrix` - When supplied, the projectionMatrix parameter allows for complete application control of all **projection** matrix parameters - including field-of-view, near/far clipping planes, aspect ratios etc, e.g. using `new Matrix4().projection(...)` or `new Matrix4().ortho(...)` etc..

Extends `Viewport`. Creates a `Viewport` with a view matrix that is placed in the player's position, with a controllable direction and orientation:

- `direction` (`Vector3`) - player direction

- `up` (`Vector3`, `[0, 0, 1]`): specifies the camera up direction

- player `direction`

- camera `direction`, relative to player direction (additive to player `direction`)

- camera `distance,` from player

See comments under `OrbitViewport` below.

Creates a viewport with a special perspective projection matrix with a FOV that works with mapbox-gl, and a view matrix that follows mapbox-gl's undocumented internal bearing/pitch/altitude conventions.

`isMapSynched()` would return false for a `Viewport` (Note: not a `Layer`):

* If `position` is specified

We could also check zoom levels etc, potentially moving all mapbox limit checks into the `WebMercatorViewport` viewport.