Expressing orientation

Reference to item: 

This issue came up when looking at the documentation for Blikk. It is a recurring issue for complex modern and contemporary art installations. In particular it is not clear how to describe the direction that an object points to, i.e. orientation of a physical thing. Relevant issues or messages about this in the SIG list or CRM website are not obvious. Rob also explained how this information is important for identifying positions of photographs and deduct position of depicted objects.

Solution 1
Direction/orientation of an object requires an axis. Defining the direction axis of an object may not be obvious in many cases, but it is obvious when we are dealing with projectors, cameras, or objects featuring a central visual item or decorative motif. The axis is a line on the object which can be defined using P59 has section.
Direction is an angle (or two angles for 3D directions), so it can be expressed as one or two instances of E54 Dimension. This requires a line from which to measure the angle. The line can be defined using P59 has section on something (e.g. the gallery floor). Not sure if it needs P157 is at rest relative to, probably not.

Solution 2
Following further discussion and thinking, this appears to be possible to encode using CRMgeo. I.e. the coordinates for the position of something will include x, y, z, φ, θ, i.e. three-dimensional coordinates plus two angles for latitude and longitude. Further discussion on the exact spatial primitive structure may be needed for such coordinates but a diagram explaining how this work alongside the relevant CRMgeo properties can be found in slide 30 of the presentation below (for 2D). This solution is a better approach to solution 1.

Relevant links

Presentation link: https://www.slideshare.net/avelios/linked-conservation-data-crmsig-prese...