Action Cams and Low-cost Multi-Frequency Antennas for GNSS Assisted Photogrammetric Applications without Ground Control Points

In civil, architectural and environmental fields photogrammetry is one of the most common solutions for deriving geometric information about many kind of objects of interest. Photogrammetric surveys suffer for the need of ground control points (GCPs), well distributed over the survey area, to scale and georeference the produced 3D data. The placement of GCPs is both time-consuming and sometimes infeasible because of environmental constraints, such as vegetation on river sides. For aerial surveys with unmanned aerial vehicles (UAV), several studies have been proposed to use the UAV GNSS antenna to reduce or eliminate the need of GCPs. This technique, called GNSS-aided photogrammetry, has been little explored for terrestrial applications despite its potential in reducing surveying time, or for integrating terrestrial and aerial surveying. This gap has been partly caused by the high cost of topographic-grade GNSS, but in recent years the market has offered receivers, such as the ublox ZED-F9P, which can achieve high accuracy at low cost. In this work we propose a simple and fast GNSS-aided methodology for terrestrial photogrammetric surveys using low-cost GNSS and image sensors. The final aim is to create a general procedure to minimize survey costs and time, and derive a scaled and georeferenced 3D information without GCPs.