What Is Aerial Photogrammetry?

Aerial photogrammetry refers to the continuous capture of images on the ground with aerial photography equipment on an aircraft, and the operation of drawing terrain maps by combining ground control point measurement, adjustment mapping, and stereo mapping.

The basic principle of aerial photogrammetry is:

Aerial photography has the following advantages:
(1) You can observe from the top;
(2) Aerial photos can objectively record various ground features observed at the same time;
(3) Recording dynamic phenomena;
(4) The aerial film is a permanent record of the status quo, and there is enough time to study it carefully, and the field scene can be moved to the room for discussion;
(5) Improve spatial resolution. ^[1]

The subject of aerial photogrammetry is the ground

Since the 1930s, there have been three main methods for aerial photogrammetry, namely

Aerial photogrammetry requires field and

Since the introduction of photogrammetry in China, domestic theoretical research in the field of digital photogrammetry has also made great progress. Under the guidance of Mr. Wang Zhizhuo's Full Digital Automated Mapping System Concept in 1978, the two sets of DPW, JX4DPW of Beijing Siwei Vision Company and VirtuoZo of Wuhan Shipu Company, passed the appraisal of the National Surveying and Mapping Bureau in 1998. These two systems integrate most of the work of photogrammetry data post-processing, and the production of aerial three surveys, 4D (DEM, DigitalElevation Model; DLG, Digital Linear Graphy; DOM, Digital OrthoPhotomap, DTM, Digital Terrain Model) products, etc. Done on that system. The emergence of digital photogrammetric workstations at home and abroad has greatly promoted the application of photogrammetry in various aspects.At the same time, these digital photogrammetric workstations have provided a variety of image processing methods after digitizing film images, which have absorbed a large number of images. Advanced technologies and theories in the processing field, such as image detection and image matching, have greatly promoted the development of photogrammetric systems.

China's theoretical progress in digital photogrammetry workstations and other aerial photogrammetry cannot hide the backwardness of aerial photogrammetry. China still has a long way to go in terms of airborne POS system, optical imaging lens, CCD production process and level. Therefore, an important content of the development of aerial photogrammetry in China is the development of digital aerial photography equipment with independent intellectual property rights. Without its own digital aerial camera, the most front-end product of aerial photography, all aspects of digital aerial photography, such as the formulation of photographic specifications, fully automatic / semi-automatic digital photogrammetric workstations, and the application of digital aerial photography will be limited. The Optical-Mechanical Research Institute of the Chinese Academy of Sciences, the Chinese Academy of Surveying and Mapping, and Wuhan University have all done a lot of fruitful research work in this area. It is with the support of these scientific research results that in 2007 the domestic digital aerial camera SWDC-4, jointly developed by the China Academy of Surveying and Mapping Science, Beijing Siwei Foresight Company, Capital Normal University and other units, passed the products organized by the State Bureau of Surveying and Mapping The appraisal meeting ended the status quo of China's lack of domestic digital aerial cameras.

SWDC-4 wide image format digital aerial camera has made breakthroughs in technical indicators such as elevation accuracy, side angle of view, weight-to-volume ratio, interchangeable lenses, and reduction in altitude. The adopted large field of view angle, elephant element angle, and large base height ratio technology have significantly improved the mapping efficiency and elevation accuracy. When SWDC was flying at 5000H, the lateral coverage width was nearly 9 kilometers, the course coverage was nearly 8 kilometers, and the 60% overlap time-to-height ratio was nearly 0.59 / 0.89. SWDC-4 has higher operating efficiency and accuracy than DMC and other foreign digital aerial cameras. SWDC-4 has higher practical value when it is used for aerial photography of small and medium scale mapping. SWDC's unique component self-powered structure and the presence or absence of photographers can work on a variety of flight platforms with great adaptability. SWDC-4 can perform aerial photography at a scale of 1: 500 to 1: 10000. Its working accuracy is much higher than that required by national standards, and its altitude accuracy reaches 1/10000 altitude. ^[3]

1. Integrated digital aerial camera

Although digital aerial cameras can overcome the disadvantages of conventional aerial photography, eliminating the recognition of high spatial resolution sensors and LIDAR technology will replace aerial photogrammetry. However, with the gradual completion of national basic terrain data and the gradual diversification of aerial photography data applications, a single black-and-white or true-color aerial camera cannot fully meet the needs of such diverse aerial photography applications. Digital aerial cameras outside the country, such as DMC and UCD, already have full-color and color infrared bands, which are typical representatives of this situation. However, this band composition is only an integration of the color infrared camera and the black-and-white camera of conventional aerial photography, which does not meet the requirements of multispectral aerial photography. The digital aerial camera integrates multispectral sensors into the digital aerial camera on the basis of continuously improving its basic functions and performance stability, so that digital aerial photography can not only meet the needs of traditional mapping, but also provide continuous in-depth remote sensing applications. Richer on-board data.

2. Automatic or semi-automatic full digital photogrammetry workstation

The application of digital aerial camera and its near-ground lightweight digital aerial photogrammetry system will have a huge impact on the photogrammetry workflow and subsequent data processing, and may have revolutionary changes. After the digital aerial camera is applied to the entire photogrammetry process, photogrammetry and other non-photogrammetric remote sensing data acquisition will be more integrated. Considering the high geometric accuracy of photogrammetric images, acquiring remote sensing data for non-mapping together with it may avoid remote sensing data processing, such as mismatching with space vector data accuracy, position mismatch between 2SWDC-4 digital aerial cameras, etc. Problems encountered. The cost of digital aerial camera image acquisition and the cost of image storage will be greatly reduced. The course overlap of more than 60% and the side overlap of more than 30% required by conventional aerial photogrammetry will not be a constraint for digital aerial photogrammetry. Highly redundant aerial photogrammetry with lateral overlap of over 60% will likely replace conventional aerial photogrammetry with low overlap. The same feature points will be reflected by more images, the number of stereoscopic image pairs of photogrammetry will be greatly increased, and the image processing methods of conventional digital photogrammetry workstations will be replaced by more automatic and semi-automatic processing methods. Full-automatic digital photogrammetric work station will become the next stage of development of digital measurement workbench. A large number of new technologies and methods will be applied to the full-automatic digital photogrammetry work station. The adoption of digital aerial photography systems and the introduction of a large number of image matching, pattern recognition, computer vision technology, parallel computing technology, and grid computing technology enable a large number of tasks that originally required human-computer interaction to work fully automatically, which will greatly enhance aviation Efficiency of photographic data processing. The development of a fully automatic digital photogrammetric workstation based on a high-performance desktop computer will become another focus of research in the field of photogrammetry. Among them, multi-vision vision-based image matching and azimuth element solution technology, elevation-accurate large-scale map rapid mapping and updating technology, high-redundant mesh aerial photography processing technology, and automatic regional cross image pair digital mapping Technology will become the key technology of automatic or semi-automatic full digital photogrammetry workstation.

3.Digital photogrammetric grid and quasi-real-time photogrammetry

The strong vitality of aerial photogrammetry lies in its continuous absorption of the latest theories and technologies in related fields.The development of local area networks, the World Wide Web, and grid technology will inevitably make digital photogrammetry introduce the latest theoretical research results, integrating computer networks, cluster processing, The latest technologies such as parallel processing are applied to aerial photogrammetry post-processing. Digital photogrammetry grid integrates a single digital photogrammetry workstation, cluster processing system, grid processing system, etc., and it is possible to realize real-time or quasi-real-time photogrammetry. We believe that after several years or ten years of development, after aerial photography aerial work is completed, digital orthophotos can be provided to users within one day, and digital photogrammetry will usher in another peak of development and application. ^[3]