Scale Bars vs GCPs

[James]

I recently scanned an interior space using photoscan's coded targets (which are amazing and all detected perfectly, but beware of reflections in windows and mirrors!) and a tape and handheld laser distometer to measure between them to generate a 'network' of 'triangulated' scale bars. After optimising the errors were very low, comparable to when using a total station to get full xyz coords for each target.

Assuming my scale bars were accurate to within a few mm, is there any reason why this approach would be less robust than acquiring full xyz coords for each marker? I assumed that by obtaining measurements between 'triangles' of markers, the network would be constrained to optimise to a fairly good solution.

I understand that this approach will not give me a good 'up' direction, but if i'd thought of it i could have helped this by using three markers on the floor.

Any thoughts? Thanks!

James