Write a guide on spatial coordinate systems

[niksirbi]

This issue is branching off #69, because we decided it would make sense to introduce coordinate systems as a standalone guide/page, complete with schematics, similar to what we have for movement datasets.

It could also necessitate adding some additional terms to the glossary, which can be cross-references in this guide.

Contents

A rough list of concepts we'd like to cover:

• Center pixel-aligned systems
• Cartesian vs Polar space
• Image / Camera / World coordinate systems
• Allocentric vs Egocentric systems
• Static vs moving reference frames?
• right hand rule
• Linear algebra:
  • linear transformations
  • origin
  • translation
  • rotation
  • scaling
  • right-hand rule
  • (free) vector

Useful resources

• SLEAP's center pixel-aligned system
• The right hand rule
• free vector
• Freya Holmér's schematic on 3D space and handedness
• Geometry of image formation
• Zulip topics:
  • on coordinate systems and reference frames
  • on movement metrics