  Photogrammetry is a science dealing with obtaining reliable information about
physical objects using their imagery description. Recent advancements in the
development of Virtual Reality (VR) can help to unlock the full potential
offered by the digital 3D-reality models generated using the state-of-art
photogrammetric technologies. These models are becoming a viable alternative
for providing high-quality content for such immersive environment.
Simultaneously, their analyses in VR could bring added-value to professionals
working in various engineering and non-engineering settings and help in
extracting useful information about physical objects. However, there is little
research published to date on feasible interaction methods in the VR-based
systems augmented with the 3D photogrammetric models, especially concerning
gestural input interfaces. Consequently, this paper presents the PhotoTwinVR --
an immersive, gesture-controlled system for manipulation and inspection of 3D
photogrammetric models of physical objects in VR. Our system allows the user to
perform basic engineering operations on the model subjected to the off-line
inspection process. An observational study with a group of three domain-expert
participants was completed to verify its feasibility. The system was populated
with a 3D photogrammetric model of an existing pipe-rack generated using a
commercial software package. The participants were asked to carry out a survey
measurement of the object using the measurement toolbox offered by PhotoTwinVR.
The study revealed a potential of such immersive tool to be applied in
practical real-words cases of off-line inspections of pipelines.
