Ortho-photogrammetry for prefabricated energy-efficiency retrofits

Panel-based prefabricated retrofits of existing building envelopes are considered a promising strategy for improving energy performance and reducing greenhouse gas emissions. These projects typically require some form of 3D model of the as-is building geometry, in order to construct the panels offsite, and, currently they tend to use laser scanning for this purpose, because of their accuracy requirements. However, laser scanners must be operated from a tripod, and producing drawings from scans is a largely manual process involving unwieldy amounts of data. We propose a line-photogrammetric approach that requires a small number of photographs (typically 8), that we call 'Ortho-Photogrammetry'. Ortho-Photogrammetry is parametrised by axis-aligned planes and produces rectified geometry suitable for panel construction. It does not require a calibrated camera or targets. We demonstrate that it is sufficiently accurate to support prefabricated retrofits, even when used with photos from a consumer UAV.