Hi martinb,
yes, I would like to orient it to an existing local coordinate system.
On the other hand, I would want to have some metrological basis.
The way you suggested ist the standard process - stick targets to the object, measure them and then take the images.
There are a number of difficulties though: for one thing in my field (buildings) it is very often very difficult if not impossible to get targets everywhere you want (or need); secondly, they can sometimes obscure features or it ist not possible to attach them (colour coats or tapestry); and thirdly, it is just one more thing to do (and plan ahead) and since control points are often necessary anyway, i might as well use them as my personal markers.
Just an idea…