Photogrammetric Surveying & Remote Sensing

It has been more than one and a half century since a French scientist first demonstrated the use of photographs in topographical surveying. A balloon was used for taking the aerial photographs at that time. Although the aerial platform was moved to kites some thirty years later, the camera was not put on an airplane until its invention at the beginning of the 19th century. Today, Hong Kong is photographed from time to time by an aerial camera and the Earth is being "watched" all the times by satellite sensors. 

Photogrammetry is the making use of photographs for spatial measurement and interpretation. Although most applications of photogrammetry involve the use of aerial photographs, ground taken photographs are also used. While photogrammetry is commonly reckoned as one kind of remote sensing, the term "remote sensing" itself broadly means the collection of information from a distance. In the surveying field, remote sensing is commonly referred to the use of satellite images for metric and interpretative purposes. The integration of GIS and remote sensing data is playing an important role in the urban planning and development monitoring all over the Pearl River Delta region.

In Hong Kong, aerial photography is largely employed for mapping, engineering, photo interpretation and recording purposes. The HKSAR Government keeps an archive of metric standard aerial photographs covering the whole territory of the current year and those years as early as 1963.

Being the third generation of the technology, digital photogrammetry is run on computer platforms. Therefore, more land surveyors can now practice photogrammetry without huge investment in photogrammetric machinery. In consequence, photogrammetric products and services become more accessible by users of spatial data.

- Photo-interpretation 
- Photogrammetric mapping
- Photogrammetry for engineering purposes such as digital terrain modeling, topographical survey and monitoring 
- Extraction of spatial data such as building heights, ground features and land boundaries 
- Orthophoto and image map production 
- Rectification and geo-referencing of satellite images 

Land Surveyor from Air Survey Unit 
of Lands Department is taking aerial images
(Courtesy: SMO, HKSAR Government)

3-D Visualization of City Model 
Produced by Digital Photogrammetry