Opened 15 months ago

#127 new enhancement

Map Editor: Replace angles with quaternions

Reported by: Carsten Owned by:
Priority: normal Milestone:
Component: other Version: svn-head
Keywords: Cc:
Platform:

Description

In the Map Editor and in the .cmap map files, we still use triples of angles (heading, pitch and bank) in order to describe the orientation of map primitives and map entities.

This however is fraught with problems: The use of angles suggests an intuitive and easy to understand method to specify the orientation of an object, but it turns out that that is a serious misconception.

Applying or using angles requires additional, implicit knowledge:

  • In what order must the rotations about the angles be applied?
  • Will a positive angle rotate clockwise or counter-clockwise?
  • Do all-zero angles correspond to the identity transformation?

That is, both humans who read a .cmap file in a text editor as well as all any code that converts to and from angles must be acutely aware of these details, and follow them in the exact same manner.

As a result, for specifying the orientation of objects, we should replace angles with the basis vectors of the objects local system, or quaternions.

The use of basis vectors / the 3x3 rotation matrix would be straightforward and simple, but also be overly verbose and give room for new questions, e.g. what if we find a non-orthogonal basis in a map file?

Consequently, using quaternions as a robust, easy to understand and unambiguous method to express rotations / orientations, and their unequivocal conversions to and from rotation matrices, seems to be a logical step.

Note that the use of quaternions should only be "internally" -- graphical user interfaces in the Map Editor should still present angular representations of rotation to the user, and convert to and from quaternions as necessary.

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