Mapping a large nature reserve requires reliable aerial data, consistent image processing, and accurate spatial references for long-term environmental monitoring. Forested terrain, elevation differences, and limited ground access can make these projects particularly demanding.
In Heilongjiang Province, northeastern China, a UAV surveying project covered approximately 467 km², collecting 83,504 aerial images across 96 flight sorties. The project aimed to produce digital orthophoto maps and surface models to support ecological research, wildlife habitat assessment, and conservation management.
ICE CYPRESS Mirauge3D was used for aerial triangulation and digital orthophoto production, handling a large image dataset captured under challenging terrain and vegetation conditions.
Caption: Geographic boundary of the nature reserve in Heilongjiang Province, China.
Project Background: Mapping for Conservation
Located at the transition between the Greater and Lesser Khingan mountain ranges and the Songnen Plain, the nature reserve is an important habitat for the black-billed capercaillie (Tetrao urogalloides) and other protected wildlife.
Its landscape includes forests, wetlands, rivers, and gently rolling hills. Monitoring changes across these environments is essential for understanding habitat conditions, assessing vegetation coverage, and planning conservation activities.
To establish a reliable spatial dataset, the project adopted a UAV photogrammetry workflow designed around 1:2,000-scale mapping requirements. A Pegasus F200 aerial surveying system was used to capture high-resolution imagery, while Mirauge3D and supporting processing software were employed to produce the mapping deliverables.
The resulting orthophoto maps would provide a common geographic reference for ecological surveys, reserve management, and future monitoring activities.
Mapping Challenges Across a Complex Forest Environment
Large-area aerial mapping presents several technical challenges, particularly when the survey area contains dense vegetation and limited accessible ground locations.
The project encountered three major difficulties.
Limited Ground Control and Complex Terrain
The reserve’s remote location, extensive forest coverage, and unreliable network CORS signals made ground control point (GCP) placement difficult.
Elevation varied from approximately 300 to 600 metres across the survey area, requiring careful flight planning and reliable image positioning.
Image Variations Across Multiple Flights
Aerial photography took place during spring, when vegetation conditions were changing rapidly.
Differences in vegetation growth, lighting, flight altitude, and image texture introduced variations across the dataset. These conditions increased the complexity of image matching and orthophoto mosaicking.
Processing a Large Image Dataset
The surveying team collected more than 83,000 images over multiple flight sorties. Processing this volume of imagery required stable aerial triangulation, efficient data management, and consistent results across different survey blocks.
Maintaining continuity between adjacent flight areas was particularly important for producing a usable orthophoto map of the reserve.
Caption: UAV flight planning across the nature reserve, accounting for terrain and survey coverage.
UAV Survey and Photogrammetry Workflow
Aerial Data Acquisition
The surveying team used a Pegasus F200 UAV equipped with a 42-megapixel nadir imaging module.
The mission was planned with a target ground sampling distance (GSD) of 14 cm, approximately 75% forward overlap, and 70% side overlap.
The field survey was completed over 22 days, covering the reserve through 96 flight sorties and generating 83,504 aerial images.
Post-processed kinematic (PPK) positioning was used to obtain precise image position data, reducing reliance on extensive ground control point placement.
After collection, the imagery underwent quality checks, positioning calculations, distortion correction, and colour adjustments using the UAV system’s supporting software.
Caption: Position distribution of aerial images collected across multiple UAV flight sorties.
Large-Scale Aerial Triangulation with Mirauge3D
Following image preprocessing, Mirauge3D was used to perform aerial triangulation on the large-scale dataset.
The software supports photogrammetric processing under challenging conditions, including low-texture areas, sparse ground control points, elevation differences, and imagery acquired across multiple flights.
For this project, Mirauge3D enabled the surveying team to submit the dataset as a single project for aerial triangulation, avoiding the need to manually divide the task into separate processing projects.
This approach helped simplify project management and maintain a consistent processing workflow across the reserve. For technical background on processing very large image datasets, see ICE CYPRESS’s research on fully distributed bundle adjustment.
Digital Orthophoto Production and Mosaicking
Once aerial triangulation was completed, the project proceeded to digital orthophoto production.
The imagery contained visible differences in brightness, colour, and vegetation texture due to changing environmental conditions during data acquisition.
Mirauge3D’s orthophoto mosaicking workflow supported seamline optimisation and image integration, helping produce consistent mapping outputs across adjacent flight areas.
Seamline refinement was especially important in forested and uneven terrain, where visual discontinuities can affect the quality and interpretation of the final orthophoto.
Caption: Seamline optimisation during digital orthophoto production.
Project Results: Spatial Data for Ecological Monitoring
The integrated UAV surveying and photogrammetry workflow produced two primary spatial data products:
Digital Orthophoto Maps (DOM)
Georeferenced aerial imagery providing a detailed, consistent view of land cover, vegetation distribution, water bodies, and other surface features.
Digital Surface Models (DSM)
Elevation-based representations of the terrain and above-ground features, supporting spatial interpretation and subsequent geographic analysis.
Together, these deliverables established a spatial data foundation for ecological research and reserve management.
The project also demonstrated Mirauge3D’s ability to handle extensive aerial imagery within a unified aerial triangulation and orthophoto production workflow, despite challenges associated with sparse control points, low-texture surfaces, and multi-flight data.
Caption: Digital orthophoto map generated from the UAV survey.
Caption: Digital surface model produced through the integrated photogrammetry workflow.
Supporting Ecological Research and Conservation Management
The value of the mapping project extends into the reserve’s ongoing scientific monitoring activities. The orthophoto maps provide a consistent spatial reference that researchers can use alongside field surveys, wildlife observations, and environmental datasets.
Forest and Vegetation Monitoring
Orthophoto maps allow researchers to examine vegetation patterns, identify forest management boundaries, and support the selection of long-term ecological monitoring plots.
When combined with field observations, these spatial datasets can assist with forest resource surveys, habitat assessment, and vegetation monitoring.
Wildlife Habitat Research
The reserve conducts wildlife monitoring through field surveys and infrared camera systems.
Orthophoto maps help researchers understand the spatial relationships between monitoring locations, habitat features, and animal activity areas.
By integrating camera observations and tracking data with georeferenced maps, conservation teams can better visualise wildlife distribution and movement patterns.
Caption: Wildlife monitoring supported by spatial mapping and infrared camera observations within the nature reserve.
Conclusion
The Heilongjiang nature reserve project demonstrates how UAV photogrammetry and large-scale image processing can support environmental monitoring across extensive, difficult-to-access landscapes.
By processing 83,504 aerial images and supporting digital orthophoto production under challenging field conditions, Mirauge3D played an important role in developing the project’s spatial data foundation.
The resulting maps and surface models provide a practical reference for ecological surveys, wildlife habitat research, vegetation monitoring, and long-term conservation management.
For surveying organisations, geospatial service providers, and environmental research teams working with large aerial datasets, Mirauge3D offers a scalable photogrammetry workflow for aerial triangulation, orthophoto production, and 3D spatial data processing.
Explore Mirauge3D Automatic Image 3D Modeling System to learn more about its photogrammetry and large-scale mapping capabilities.
*Case material adapted from the original project documentation, with information provided in part by the nature reserve administration.
