Issue with Spatial Orientation subclasses

[cameronmore]

A Spatial Orientation is "A Relational Quality that is the angle of Rotation of an Object relative to one or more Plane of Reference or Axis of Rotation.". But Axis of Rotation is a Spatial Region, which cannot bear any qualities.

Shouldn't Axis of rotation be a subclass of Fiat Surface? The only concern might be that Continuant Fiat Boundaries are defined relative to Material Entities and I'm wondering if there would ever be a case where an axis might be defined relative to an immaterial entity.

[alanruttenberg]

This should not be relative to axis of rotation, because there are relative orientations between e.g. two vehicles. Axis of rotation would be a subclass of fiat line. Use a plain fiat line. Axes can be defined relative to immaterial entities, e.g. the normal to a surface. Also it is one or more angles (plural). E.g. the Tait-Bryan rotation consists of 3 rotations, one from each axis of a Cartesian coordinate system. Also an orientation can be specified by a vector and a twist.

[cameronmore]

What should spatial orientation be defined in terms of rather than an axis of rotation? And if they should be decoupled, shouldn’t definitely move axis of rotation out from under Spatial Region since those are not defined in terms of material entities, i.e. things which rotate / spin?

I am definitely not an expert in this area and am just thinking out loud

[alanruttenberg]

Generally speaking they are defined by rotations of one flavor or another between coordinate systems anchored in some way on the entities. The way I do it in my work is that I define relative orientation without reference to landmarks, because a) you've have to talk about coordinate reference systems and b) as with altitude I don't think it should be required to be defined in terms of fiat points. See here and here.

A relational quality that inheres in two independent continuants each of which has relative orientation to the other

Not a great definition - circular, but I didn't have a better one at the time. I give an example

the position and relative orientation of two rods attached by an articulating joint

and a note

the relative position and orientation, like all qualities, can change in time

Then I let information entities do the work, describing a relative orientation quality by one of the ways orientation can be defined - there are several, but all are equivalent to rotations in space. I mention one: Tait-Bryant. There are also Euler angles, quaternions, and vector+twist (one angle contra my statement that it is angles plural), or pitch, yaw, and roll.The quaternions are equivalent to 3 angles but are not actually angles). Time is noted by relation on the information entity - more specifically, value specifications both. If you haven't seen the value specification proposal I can send it to you.

Note that orientation is not always defined - there is no relative orientation between two perfect spheres. You have to have enough asymmetry to define a coordinate system on it. Between two cones there's only a single rotation needed, defined by the angle between two lines from apex to center of base. Between two cylinders are also an angle, but it is ambiguous because you can't give either axis of symmetry a direction. Ellipsoids are like cylinders but the symmetry is broken, when talking about planetary bodies, by choice of one end as north.

Maybe:

A relational quality that inheres in two independent continuants that can be rotated so that they are aligned in some way.

and add a note about spheres, cones, cylinders etc.

If you wanted to do the same treatment as they did with altitude it would be complicated, because you can define it wrt 4 points on each entity, or a surface and and two points, or a surface and a point and a direction.... And you have to exclude the cases where there isn't enough asymmetry (the spheres, cones, etc). I prefer to keep it simple. If someone wants to define fiat points or surfaces or lines in order to describe the rotations there's nothing preventing them from relating them to the relational quality with 'specifically depends on'.

There are other issues. Pitch, yaw and roll only seem to be defined for moving objects, but ask perplexity.ai: "are pitch yaw and roll only defined for moving objects?"