The role of GPS aerial triangulation in photogrammetry

Development and prospect of digital photogrammetry

After the research, development and popularization of digital photogrammetry in 1980s and 1990s, digital photogrammetry in China has developed at an unimaginable speed in the 20th century. Digital photogrammetry workstation has been widely used and popularized in China's photogrammetry production, and the teaching of photogrammetry has also been greatly popularized from the aristocratic teaching that only a few universities could carry out in the past. At present, at least 40 colleges and universities in China offer photogrammetry courses for surveying and mapping engineering majors, which greatly broadens the training channels for talents needed for photogrammetry.

Due to the transformation of photogrammetry production, image scanners have been widely used, and the number of scanners in China has exceeded 100. At the same time, the introduction of aerial cameras is also accelerating. This paper also introduces the GPS/IMU system used in aerial photography and the digital aerial camera of Z/I company.

It has been applied in China.

At the same time, the application of high-resolution remote sensing images and their positioning parameter files can quickly generate orthophoto images with few field control points, which has been more and more widely used in urban and land change and planning. The more aerial laser scanning radar.

More and more mature. All these indicate that the rapid development of the new generation of sensors and positioning systems and the large-scale popularization of digital photogrammetry workstations have raised a very serious and realistic question for the development of photogrammetry itself: where is photogrammetry going?

New opportunities for the development of digital photogrammetry

Since the beginning of the 20th century, photogrammetry characterized by pure precision and optical analog photogrammetry instruments has been carried out for more than half a century. During this period, the teaching of photogrammetry and a very small amount of scientific research, except the theoretical research of the so-called transformed beam, were mostly around several works in Europe.

Analog photogrammetry instruments produced by famous manufacturers. By the end of 1950s, computers began to enter photogrammetry, and the research fields of photogrammetry were greatly expanded, such as analytical aerial triangulation, online aerial triangulation, adjustment of regional network, gross error detection theory, orthorectification,

Digital mapping, etc. With the advent of the digital photogrammetry era in the 1990s, compared with the traditional analog and analytical photogrammetry, its greatest feature is that computer vision and pattern recognition technology are applied to photogrammetry, and internal orientation, relative orientation, aerial triangulation and digital elevation measurement are realized.

(semi-) automation of DEM generation, etc. Digital photogrammetry not only computerizes all the functions of traditional photogrammetry instruments, improves work efficiency and reduces the requirements for operators, but also continuously expands the functions of photogrammetry.

However, we must be soberly aware that some digital photogrammetry workstations are only substitutes for analytical mapping machines; At present, digital photogrammetry workstation is mainly suitable for aviation and aerospace photogrammetry, but close-range and ground photogrammetry are quite different from it. Use digital photogrammetry.

To apply quantity to close-range photogrammetry, the theory of photogrammetry must be further developed; Even in a highly automated digital photogrammetry workstation, the main research of photogrammetry is only on the image matching technology of "homonym points". Therefore, we must jump out of the traditional photogrammetry.

The theoretical development of digital photogrammetry must be considered from the characteristics of computers, which is a brand-new opportunity for its theoretical and practical development, such as vanishing point theory and application, generalized point theory and application, multi-baseline stereo theory and application.

Important direction of digital photogrammetry development

At present, the technology of directly obtaining digital images, DEM, camera position and attitude data is developing rapidly, which will play an increasingly important role in speeding up the mapping cycle of photogrammetry and reducing the workload in the field. For example, the use of high-resolution satellite images and the corresponding rationality

Using the polynomial coefficient (RPC) to locate the data file, and then using a very small number of GPS points to control it, we can quickly make an orthographic image of 1: 1, 000 or even 1: 5000. But what is the development and task of photogrammetry itself? This is a question that photogrammetry workers must answer.

No matter how the data acquisition means develop, one of the central tasks in the development of aerial (aerospace) photogrammetry is to update the data, so as to realize the mechanism of establishing the national basic topographic map from regular update to dynamic update. Especially for China with rapid economic development, GIS data update is particularly important.

Especially important.

However, data update is not a re-measurement of topographic map, specifically:

The complexity of data updating surveying and mapping with aerial images, even though the production process and various specifications have matured in the simulation mapping period, the process of photogrammetry has changed a lot in the analysis era, especially digital photogrammetry, but the basic tasks and specifications,

Fan has not fundamentally changed. The data update is different, and its situation is much more complicated than "new test or retest". Its complexity comes from how to use the existing data, reduce the workload in the field and in the office, and speed up the drawing cycle. There are many problems that must be considered, such as:

What data are available? Orthophoto +DEM, or line drawing +DEM? Where is the data updated? Is it urban, suburban or mountainous? Is the scale of the updated topographic map large or small? Wait a minute.

For example, when the data of suburban, mountainous and small-scale maps are updated, the "new image" can be directly registered with the existing "orthophoto +DEM" for aerial triangulation without (or without) control points. However, it is difficult to use the existing orthophoto map for updating the city and large-scale topographic map. When updating cities and large-scale maps, it will be more beneficial to use existing line drawings than image maps.

Data updating involves the innovation of photogrammetry theory and the updating of technology. The problem of data updating is how to use the existing "data", more accurately, how to use the existing "information". As we all know, in order to update the existing map with new images, it is most important to "overlap" the two.

One step away. So as to determine the orientation elements of the image, correct the image into an orthographic image consistent with the map, and then nest "map" and "image". Therefore, in data updating, besides the traditional manual selection of points as control points, can a large number of maps be used?

As a control, "linear element" is very important to realize the automation of data update and improve work efficiency.

Data updating involves change detection, and the establishment of dynamic updating mechanism brings the demand for data updating due to the change of features and landforms. With the more and more extensive application of surveying and mapping results, especially the development of geographic information industry, the application of surveying and mapping results has surpassed economic and national defense construction.

Category, and into people's lives. For example, with the widespread use of car navigation, people have high requirements for road renewal, so "periodic renewal" can no longer meet the requirements, and its formulation is unscientific. Instead, a "dynamic update" mechanism should be established as needed.

In order to establish a dynamic updating mechanism, the technical core is "change detection". Although there has been a lot of research on change detection at home and abroad, most of them are only a few experiments on certain elements, which is far from practical use. For the dynamic updating mechanism of the basic topographic map of the State Bureau of Surveying and Mapping, the technical route of "from coarse to fine" can be adopted. For example, when updating the1:50,000 national topographic map, it is necessary to determine whether the 1: 1 10,000 national topographic map needs to be updated by counting the change rate of the map, thus establishing a more reasonable and practical dynamic updating mechanism of the national basic topographic map.

Data updating involves the updating of concepts and the revision of specifications. Traditional photogrammetry is divided into field control points, indoor encryption points and breaking points. The encryption points are obtained by field control points and aerial triangulation, and finally the broken points are mapped.

Of course, the requirement of accuracy is "the superior is higher than the subordinate" and "the superior controls the subordinate". Indoor mapping is mapping the breakpoints of topographic maps under the control of encryption points, or orthorectification, so the accuracy of encryption points is higher than that of breakpoints and images on topographic maps.

The obvious point in the picture. However, in the above data updating methods, more consideration is given to the application of broken points or obvious points on topographic maps or image maps as a new round of cartographic control (note: the number of broken points used for control is dozens or even dozens of times that of traditional control points.

A hundred times), resulting in a new round of maps, but whether it can meet the requirements of the map, of course, requires a lot of verification. At the same time, the updating scheme should and must consider adding a small number of field control points, and making use of the external orientation elements, encryption points and corresponding shadows of the image for the last round of mapping.

For example, the application of POS data should be considered when possible. However, no matter which scheme is adopted, most of them involve the renewal of traditional concepts and the revision of corresponding norms.

A new field of photogrammetry development

Up to now, the development of digital photogrammetry, whether in theory or in practice, mainly revolves around the use of aerial (aerospace) photogrammetry to map topographic maps, while there is little research on digital close-range (ground) photogrammetry. At the same time, with the wide application of digital cameras and the reduction of prices.

The grid is getting cheaper and cheaper, and the application of digital camera in measurement will be the inevitable trend of photogrammetry development.

In this field, nature is closely related to computer vision, because "the research goal of computer vision is to make computers have the ability to identify three-dimensional environmental information through two-dimensional images, which will not only make machines perceive the geometric information of objects in three-dimensional environment, including their shapes, positions, postures, movements and so on. , but also to describe, store, identify and understand them ",which is very similar, but there are obvious differences. Similarly, digital close-range photogrammetry is very different from traditional close-range photogrammetry based on single baseline stereo and target.

Digital photogrammetry should be a relatively young subject. Because of replacing "human eyes" with computers, digital photogrammetry will develop rapidly both in theory and in practice. It will be used for 3D visualization, geographic information data updating and digital close-range photogrammetry.

And other aspects have been widely applied and developed. It will become more and more important to update the national basic map and its present situation.