Digital mapping takes off in China

Digital mapping takes off in China

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Wang Wenjie
Wang Wenjie
General Manager
Intergraph Mapping and Geospatial Solutions, China
The pace of development in China’s major cities is among the fastest in the world. For the government departments that plan and administer this development, having up-to-date land use data has become critical, and is also needed for meeting central government requirements for detailed information on planning and land use

The pace of development in China’s major cities is among the fastest in the world. For the government departments that plan and administer this development, having up-to-date land use data has become critical, and is also needed for meeting central government requirements for detailed information on planning and land use. Because of the fast growth pace that spurs a changing landscape, it is necessary to capture imagery for cities, such as Beijing and Shanghai, around every six months to create the updated orthophotos and digital terrain models (DTMs) needed for this planning and construction. Till late 2003, only film-based analogue mapping cameras were used in China to capture new imagery of the country. This meant substantial turnaround times from image capture to orthophoto and DTM generation due to manual processing and scanning procedures, slowing the availability of up-to-date maps. In addition, current mapping data used by many government authorities was out-of-date, and unsuitable considering the rate of development.

With demand for up-to-date photogrammetric products growing more rapidly than photogrammetric firms’ capability to address these needs, digital data acquisition offered an attractive alternative to traditional film-based acquisition because of its decreased cost and shortened delivery times. Additionally, current digital aerial cameras offered many innovations that ensured the capture of precise and accurate imagery under various weather conditions.

The advent of digital aerial camera technology represented a new opportunity for companies to provide extremely accurate imagery with much faster turnaround times. However China’s tight-knit commercial remote sensing and photogrammetry industry was sceptical of the new technology. The local industry had no experience with digital mapping cameras, and there was some confusion about the different technologies offered by vendors, such as the choice between linear or frame systems. This resulted in reluctance by Chinese companies to be the first to invest in a digital mapping camera.

Beijing Xing Tian Di, one of China’s leading high technology companies, is leading the switch to the use of digital aerial camera technology. They began investigating whether it was feasible to buy a digital aerial camera to replace the existing rented film-based camera. To meet customer demand, they required a system that could capture large-scale imagery below 1:5000, as well as smaller scale imagery of 1:25000. For this reason, it was determined that a frame sensor-based camera was most suitable because a wide application range could be covered, very similar to the large format, film-based aerial camera. The full frame sensor also had a feature called Time Delay Integration (TDI) that enables electronic Forward Motion Compensation (FMC). FMC avoids image blurring and is important for large photo scales or for long exposure times when photoflights are being conducted in low light conditions. FMC is a proven capability with analogue film cameras.

As part of the evaluation process, Xing Tian Di flew several test photo flights with Intergraph’s Z/I Imaging Digital Mapping Camera (DMC), covering Chang Zhou local airport and the city of Zhenjiang. Varying heights and scales were employed, including photo scales of 1:4000 and 1:7000 and heights up to 520 metres. During the photoflight of the airport, the DMC acquired 88 photos that covered 3×2 square kilometres each. The photoflight of Zhenjiang generated 2000 photos to test the full capacity of the camera. They also flew at scales of 1:6000 and 1:12000 in the Cuiping Mountain area and 1:25000 in Nanjing city. The images were checked and verified by the National Bureau of Surveying and Mapping to ensure that the images met government accuracy standards for large-scale mapping. In December 2003, Xing Tian Di decided to invest in the DMC, becoming China’s first company to purchase the technology.

Beijing Xing Tian Di leads the way for completely digital mapping environment
Beijing Xing Tian Di integrates scientific research, software development and technology trade and offers services for spatial remote sensing, geographical information systems (GIS) and global positioning systems (GPS). The three-year-old company is a leading supplier of digital terrain models and orthophotos for various Chinese government clients, including local land and planning bureaus and utilities. After securing further financial investment, and determined to gain a competitive edge by capitalising on the growing need in China for this imagery, Xing Tian Di was the first company in China to acquire a digital aerial camera. They also recently purchased a second DMC to meet increasing customer demands.

Around seven months after evaluating and then purchasing the new technology, Xing Tian Di has taken around 60,000 photos using the digital camera, averaging 2,000 photos per flight compared with 400 to 800 photos per flight using the previous film-based camera. Scales have ranged from 1:25000 to 1:4000. Xing Tian Di has completed major projects in Nanjing city and Zhenjiang city, with projects in preparation for Tian Jin city and flights of several gorges. Jiang Su province was among the first to receive imagery from the digital camera, with Xing Tian Di completing more than ten projects within a very small area.