What on Earth?

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Overview ​

What on Earth? introduces a small Domain-Specific Language (DSL) for working with 3D scenes. The DSL helps you create and control points, lines, and shapes to manage satellite positioning, orientation, and visualization.

Before proceeding, here are some useful things to know about how the app works:

Useful information! ​

Quaternions are in xyzw order ​

All functions that take quaternions expect a [number, number, number, number] and this should be provided in xyzw order! Functions that return quaternions will also follow this convetions.

App state is maintained across script executions ​

The app maintains the state of the 3D scene between consecutive script executions. This means any points, lines, or transformations you create will remain until you explicitly reset the state. To clear everything and start fresh, you can call:

javascript
reset();

Default Points and Lines ​

To make it easier to get started, the app initializes with these default elements:

  • Point: "sat"

    Represents a satellite positioned at a predefined location. It is an OrientedPoint with a local frame and can be used as a reference for orientation and transformations.

  • Line: "nadir"

    Represents the satellite's nadir, the line connecting the "sat" point to the center of the Earth. This line is helpful for visualizing the satellite's position relative to the Earth's surface.

Supplying vectors and positions by name or value ​

Most places that expect a point can either take the name of one that has been previously defined or a [number, number, number]. Similarly there is special rules for arguments that expect a vector. Most of the time one of the following 3 will be valid:

  1. A 3-element array representing the target vector.
  2. A string of the form "startPoint->endPoint" to define a vector between two points. The special name "Moon" can be used as either start or end point to reference the Moon's current position.
  3. The name of a previously created line. It's direction will be used as input.

Accessing and Modifying State ​

The entire state of the scene is accessible through the built-in state variable. While you can manipulate the state object directly, be cautious when doing so, as improper changes can cause unexpected behavior. Most of the time, it's better to use the provided commands for managing points, lines, and transformations.

DSL Overview ​

1. Point Types ​

Learn about the Point and OrientedPoint classes, which are the building blocks for representing objects in 3D space. The OrientedPoint extends Point to include orientation, enabling operations like attitude control and visualization.

2. Movement & Attitude Commands ​

Discover commands to manipulate points' positions and orientations, such as mov, rot, and mov2sat. Tools for quaternion-based attitude adjustment are also introduced.

4. Geometry Commands ​

Explore tools for creating and managing points, lines, and angles in the scene. Examples include addPoint, createLine, and angle.

5. Camera Commands ​

Learn how to manage multiple cameras in the scene, switch between different views, and work with cameras attached to points.

6. Utility Commands ​

Access helpful mathematical and satellite-related utilities, including coordinate conversions (geo2xyz, xyz2geo) and fetching Two-Line Elements (TLE) with fetchTLE.