Abstract
Abstract. This study highlights the benefit of precise aerial position control in the context of mapping using frame-based imagery taken by small UAVs. We execute several flights with a custom Micro Aerial Vehicle (MAV) octocopter over a small calibration field equipped with 90 signalized targets and 25 ground control points. The octocopter carries a consumer grade RGB camera, modified to insure precise GPS time stamping of each exposure, as well as a multi-frequency/constellation GNSS receiver. The GNSS antenna and camera are rigidly mounted together on a one-axis gimbal that allows control of the obliquity of the captured imagery. The presented experiments focus on including absolute and relative aerial control. We confirm practically that both approaches are very effective: the absolute control allows omission of ground control points while the relative requires only a minimum number of control points. Indeed, the latter method represents an attractive alternative in the context of MAVs for two reasons. First, the procedure is somewhat simplified (e.g. the lever-arm between the camera perspective and antenna phase centers does not need to be determined) and, second, its principle allows employing a single-frequency antenna and carrier-phase GNSS receiver. This reduces the cost of the system as well as the payload, which in turn increases the flying time.
Highlights
1.1 MotivationThe majority of today’s micro aerial vehicles (MAVs) employed for ortho-photo production, for example, use indirect sensor orientation
Though the technological capabilities of the MAV system allow airborne calibration, the global navigation satellite systems (GNSS) observations are not used as additional observations in the self-calibrating bundle adjustment since they are not of sufficient quality to positively contribute to the adjustment
The first case is focused on the indirect sensor orientation approach, which is the dominant method of sensor orientation when mapping with MAVs
Summary
The majority of today’s micro aerial vehicles (MAVs) employed for ortho-photo production, for example, use indirect sensor orientation This method is very popular and effective whenever the surface texture allows for automated observation of (a large number of) tie-features. At the same time it is very well known that the precise observation of the camera perspective centers via global navigation satellite systems (GNSS) practically eliminates the need for GCPs in a block configuration of images, while improving its robustness and accuracy (Colomina, 1999) This so called AT-GNSS approach is often completed with a few GCPs to improve the redundancy and identify possible biases in GNSS positioning (Ackermann, 1992; Heipke et al, 2002). This motivates the presented investigations into removing the need for GCPs and/or reducing their number to a strict minimum
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