What makes a great oblique mapping camera? Essential design insights
17 April 2025
Over the past few years, the aerial mapping industry has increasingly recognized the advantages of simultaneously collecting nadir and oblique imagery. This combination enhances advanced data products such as 3D textured surfaces and building models while also proving value for corridor mapping applications.
But what makes a highly efficient, reliable, and robust aerial oblique mapping camera? Our successful Osprey series—led by the recently introduced UltraCam Osprey 4.2—stands out with a thoughtfully balanced design that provides the ideal foundation for the seamless generation of datasets like building models and 3D city meshes. Why? Let’s take a closer look.
To ensure consistent product data quality, it is crucial that the Ground Sample Distance (GSD) in oblique images matches that of their nadir counterparts. Due to the scaling effect of the 45-degree viewing angle, the GSD naturally varies from front to back. The key reference point for measuring GSD is at the center of the image, as outlined in the ASPRS Positional Accuracy Standards for Digital Geospatial Data (Edition 2, Version 2, 2024, p.197).
To achieve this balance, the focal length of oblique cones must be 1.414 times (square root of 2) longer than the nadir focal length. Additionally, since light travels a longer path through the atmosphere at an oblique angle, a slightly extended focal length can further improve GSD in oblique images.
Well-aligned nadir and oblique footprint sizes
When meeting tender requirements—such as full oblique coverage or forward and side overlaps (e.g., 80/60)—camera design plays a crucial role in generating efficient, robust image blocks with the necessary overlaps.
Since current oblique cones typically feature a single sensor that predetermines the footprint size, optimization can only be achieved through the nadir footprint, which must be balanced to align with the oblique footprint. The schematic below compares a balanced design (as used by Vexcel) with an unbalanced one, where the nadir footprint is too wide relative to the oblique one.
As shown in the image, a large nadir footprint alone is not enough if the forward and backward oblique footprints do not provide sufficient sideward overlap. To achieve full area coverage, the lower edges of the forward and backward oblique images must always overlap. If the nadir footprint is too large, the nadir overlap is unnecessarily increased, leading to excessive redundant data without adding real value.
Optimized orientation of left and right oblique sensors
For left- and right-looking obliques, the longer side of the image sensor should always be oriented in the flight direction to maximize efficiency. Vexcel Imaging’s oblique camera systems further enhance this approach by incorporating a sensor shift in the left and right oblique cones. This design captures more content closer to the nadir footprint, resulting in improved GSD balance.
Sharp imagery at rapid capture intervals
A fast frame rate is essential for an aerial camera, ensuring high forward overlaps even at ground sampling distances (GSD) of 2.5 cm. To achieve high-quality data products, imagery must be crystal clear and free from motion blur. Vexcel’s proprietary Adaptive Motion Compensation (AMC) technology is a game-changer and the only solution on the market that offers multi-directional compensation, eliminating all translational and rotational motion blur in both nadir and oblique imagery. This software-based solution preserves full detail in well-exposed images and low ISO settings in a scale-adaptive manner, allowing users to fully leverage the high dynamic range of the CMOS sensor. The result is consistently sharp, high-accuracy imagery—even in challenging conditions. With AMC and an ultra-fast frame rate of up to one frame every 0.7 seconds, Vexcel’s Osprey systems enable aerial mapping professionals to capture high-quality data at super high flight speeds, maximizing efficiency without compromising image clarity.
The UltraCam Osprey series embodies Vexcel Imaging’s commitment to precision, efficiency, and sound photogrammetric principles in oblique aerial camera design. By balancing GSDs, optimizing footprint alignment, and integrating cutting-edge features like Adaptive Motion Compensation (AMC), the Osprey series ensures the highest-quality data capture—even at high flight speeds. Designed for seamless automation and robust image processing, it provides the ideal foundation for generating accurate 3D city models, textured building meshes, and other advanced datasets.
If you enjoyed this content and want to receive more insights like this, follow or connect with Marc Muick, Head of Applied Photogrammetry for Camera & Calibration, on LinkedIn.
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