Oblique photography, as an advanced photogrammetric technique, uses multi-angle image acquisition and 3D modeling to provide high-precision, multi-dimensional spatial data for applications such as geographic information systems (GIS), urban planning, and building monitoring.
Compared to traditional orthophotography, oblique photography can capture side-on information of objects, generating realistic 3D models. Driven by drone technology, its application scope and efficiency have significantly increased.
What is oblique photography?
Oblique photography involves capturing surface images at a specific oblique angle (usually 30°-60°) using a camera. These images, combined with vertical (orthophoto) images, create a 3D model with realistic textures. Compared to orthophotos, which only produce two-dimensional images, the core advantage of oblique photography lies in its multi-angle data acquisition capabilities, enabling the complete reconstruction of the three-dimensional form of buildings, terrain, and complex structures.
Technical Principles of Drone Oblique Photography
Oblique photography is based on photogrammetry. In drone photogrammetry, drone images can be used to generate 3D point clouds, digital elevation models (DEMs), orthophoto maps (DOMs), and other data, providing rich data representation.
Multi-angle Image Capture: The drone is equipped with a high-definition imaging camera gimbal, either a single-lens or multi-lens system, capturing highly overlapping images from both orthographic and 45° oblique angles, covering the target area.
Feature Point Extraction and Matching: Using the SIFT or ORB algorithm, feature points are extracted from the images and matched across multiple viewpoints to form a sparse point cloud.
Camera Pose Determination: Utilizing RTK or PPK data combined with the camera pose (pitch, yaw, and roll) recorded by the IMU, the precise position and angle of each image are calculated.
Dense Point Cloud Generation: Using multi-view geometry and dense matching algorithms, a high-density 3D point cloud containing spatial information about the surface and objects is generated.
Texture Mapping and Model Optimization: A triangulated mesh is generated from the point cloud, and the original image texture is mapped onto the model to create a realistic 3D model.
Georeferencing: The model is embedded in a global coordinate system (such as WGS84 or UTM) and exported in OBJ, LAS, or 3D Tiles formats for use in GIS or CAD software.
Advantages of Drones in Oblique Photography
The widespread adoption of drone technology has transformed oblique photography from traditional aerial photography to one that is low-cost and highly flexible. With the widespread adoption of drone RTK/PPK technology, small commercial drones can easily perform high-precision mapping tasks, creating key advantages for drones in oblique photography:
High Flexibility and Rapid Deployment
Flexible Route Design: Using Autel commercial drones for pre-set missions, pilots can plan complex routes based on mission requirements, covering target areas from multiple angles and adapting to urban, mountainous, or irregular terrain.
Rapid Deployment: The lightweight equipment allows a single person or a small team to take off and collect data in minutes. For example, covering a 1 square kilometer area takes only 1-2 hours.
Low-Altitude Flight Capability: The drones can fly at altitudes of 50-150 meters, acquiring high-resolution imagery and are suitable for high-precision modeling of small areas.
The Autel EVO II V3 series, EVO Lite Enterprise series, and EVO MAX series can be quickly deployed and launched in under a minute. Pre-set flight missions can be configured in the corresponding drone software, enabling large-scale aerial surveying and mapping.
Read More: Autel EVO II Pro RTK V3 Photogrammetry
High Precision and Multidimensional Data
Centimeter-Level Positioning: Drone RTK/PPK technology combined with GCP ensures absolute positioning accuracy of 2-5 cm for models, meeting engineering surveying requirements.
Multi-Camera Systems: Professional drones (such as the DJI Matrice 300 RTK and Autel Alpha) are equipped with five-lens cameras to simultaneously capture orthophoto and oblique imagery, generating complete 3D structures.
Multi-Source Data Fusion: LiDAR, thermal imaging, or multispectral data can be combined to enhance model detail and functionality, such as detecting building heat leaks or vegetation cover.
Cost-Effectiveness and Automation
Low Cost: Compared to traditional helicopter aerial photography, drone equipment prices and operating costs are significantly lower.
Automated Processes: Flight planning, data collection, and modeling are automated using the drone's own software or third-party software, reducing the need for manual intervention.
Repeatability: Supports regular, repeated missions to generate time series models, suitable for dynamic monitoring, such as construction progress or terrain changes.
Applications of Drone Oblique Photography
Oblique imagery has a wide range of uses. The intuitive 3D models it generates are ideal for large-scale topographic mapping and urban planning.
Smart Cities: Ground feature information captured by oblique cameras can be used to quickly construct 3D models, providing city planners with consistent, reliable data for visualizing projects and evaluating the short- and long-term impacts of any smart city initiative.
Open-pit Mine Management: High-resolution 3D true mesh models are an ideal starting point for engineering operations, construction, project planning, and communication activities. Using 3D models allows for better communication with stakeholders, showcasing completed work, ongoing work, and future plans.
Planning and Design: Oblique photography can also be used in planning and design. In bridge planning and design, combining BIM technology with drone oblique aerial photography can create a 3D model of the bridge structure. Furthermore, BIM modeling allows for real-time dynamic adjustments and 3D visualization of bridge design options.
Furthermore, oblique photography technology has a wide range of applications in land surveys, rural cadastral mapping, river and lake management, real estate ownership, engineering surveying, cultural heritage preservation, archaeology, infrastructure monitoring, construction, agriculture and forestry, transportation planning, BIM design, gaming and film, and GIS information systems.
Conclusion
Oblique photography, leveraging drone technology, enables efficient and accurate 3D modeling, revolutionizing traditional surveying and mapping. Its multi-perspective and high-precision capabilities provide rich spatial information for applications ranging from urban planning to disaster response.
Read More: What is The Difference Between NADIR Images, Orthophotography, and Oblique Photography?
