Implement snap-to feature for //pose/@rotation_type conversion

[EricCousineau-TRI]

Desired behavior

Per proposal http://sdformat.org/tutorials?tut=better_pose_proposal&cat=pose_semantics_docs&, should allow conversion among rotation types (e.g. from `rpy_degrees

Alternatives considered

See proposal

Implementation suggestion

See proposal

Additional context

See proposal

[FirefoxMetzger]

@EricCousineau-TRI Is it possible to comment on proposals somewhere? Based on the motivation, I was wondering if the following alternative has been considered:

<pose>
  <value degrees="True">0 0 0 90 45 0</value>
</pose>

Making it degrees=False by default would make the entire thing backward compatible with 1.8.

[chapulina]

@FirefoxMetzger , those are hosted at sdf_tutorials, i.e. gazebosim/sdf_tutorials#37

[FirefoxMetzger]

@chapulina Thanks :) Would I create an issue there to comment on a proposal, or what is the preferred approach?

[chapulina]

Good question, I'd say it's best to open an issue here at sdformat for greater visibility. If you have specific suggestions, you could open a PR against the proposal.

[azeey]

FWIW, the option we're currently working in #589 is <pose rotation_type="rpy_radians/rpy_degrees/q_wxyz">. By default @rotation_type=rpy_radians so it would be backward compatible.

[FirefoxMetzger]

Thanks for pointing that out @azeey . I skimmed the PR and it does look like the better choice than <value degrees="True/False">.

[EricCousineau-TRI]

Closing given merge of #689