Vladimir Gulin
Marketing Director, Geokosmos, Russia
[email protected]
For last ten years the rapid grows of innovative technologies significantly changed situation in many areas of human activity. This is true for aerial survey (photogrammetry) industry as well. Two main changes are mostly remarkable. First, the place of film (analogue) aerial photo cameras is more and more taken by digital ones. Second, airborne laser scanners (LiDAR systems) became to be used for aerial survey allowing to solve both traditional and new survey tasks on principally new quality level.
Modern large format digital aerial cameras provide imagery with very high (3-5cm) ground resolution. Also, the images in several spectral zones could be collected simultaneously, thus extending possible applications of the results. Collecting data in digital form avoids any chemical procedures on film processing as well as transformation errors during data converting from analogue to digital form.
Airborne laser scanners are the effective tools for creating Digital Terrain Models (DTM) and Digital Surface Models (DSM) with the accuracy of around 15cm. Unique feature of the technology is the ability to determine true relief under canopy in forest-covered areas – no any other technology allows doing it with such accuracy at the moment.
Although both types of airborne equipment could be used standalone, sometimes their combination provides collection of data set for numerous applications. It seems that combinations of digital airborne equipment and collected by their means complex data would play significant role in developing different 3D mapping applications in coming few years.
In particular, airborne laser scanners are often used in combination with medium scale digital photo cameras. Collected laser data could be used for imagery correction to produce true orthophoto. Vise versa, digital images could be used to texture 3D models derived from laser data allowing easy recognition of surface features. It is important to mention that airborne equipment during the flight is accurately positioned by GPS (3D coordinates) and inertial navigation system (aircraft variations in different directions), so there is no need in additional surveying ground control.
Another example of equipment combination – installation of several digital cameras simultaneously collecting both ortho and oblique images. Then, using special software packages collected data could be processed for creation of photorealistic 3D models of, for instance, urban areas.
And even more powerful equipment combination is used by Russian-based Company Geokosmos during last two years. Description of that equipment complex and its possible applications is given below in this paper.
Founded in 1993 and headquartered in Moscow Geokosmos now is a leading surveying and mapping company not only in Russia, but also in many other regions. While the Company remains Russian by nature, it is active around the globe. Today Geokosmos has subsidiaries and business partners in Europe, Middle East, South-East Asia, America and Africa. The scope of Geokosmos projects is not limited by the Russian market as well. In 2005-2007 Geokosmos participated in different projects implemented in Asia, Europe, Middle East, Caribbean Region and Africa.
Today Geokosmos has one of the biggest equipment pools in the world. In particular, the company owns six airborne laser scanners (ALTM 2050/3100/Gemini manufactured by Optech Inc., Canada), two large format digital aerial cameras (UltraCAM-D/UltraCAM-X manufactured by Vexcel Imaging, Austria), eight medium format digital cameras AIC-modular-LS (Rollei GmbH, Germany) and other equipment.
Having such excellent instrumentation allowed to create unique equipment set on the board of airplane Antonov-30 consisting of: UltraCam-D large format (frame) digital aerial camera for collecting vertical high-resolution imagery; 2 Rollei AIC-modular-LS (H25) digital metric medium scale cameras for collecting oblique imagery from the left and right boards; ALTM 3100 airborne laser scanner for LiDAR survey. Main purpose of this combination is collecting of complex high-accuracy data with highest performance possible. This equipment set is mostly effective for complex survey of urban areas.
To provide illustratuon of potential of the complex let us demonstrate some results of Geokosmos project in large Russian regional and industrial centre – Nizhny Novgorod and adjacent areas. The project purpose is collecting the data suitable for its multi-purpose application by regional or city administration and individual state and private companies for urban planning and property complex management.
The used airplane ?ntonov-30 is a special aircraft widely used for aerial surveys in Russia. Photo camera and LiDAR have been installed in special holes for surveying in airplane bottom. UltraCam-D digital camera has been installed on a gyro-stabilized platform, and ALTM3100 – on a specially designed hard platform. Medium format metric cameras have been installed on specially designed small side holes on the bottom from starboard and portside. A special platform has been designed for this purpose, which rigidly fixes cameras with relation to the aircraft body in a required position to the hole to ensure a set angle. Rollei cameras have been used to take oblique images with the angle of 50 degrees, UltraCam-D camera is used for collection ortho imagery, ALTM laser scanner is used to obtain digital surface models, digital elevation models and further creation of 3D models.
The following aerial survey parameters have been chosen: flight altitude is 800m; flight speed is 320 km/h; distance between routes is 405m; route configuration is two sets of routes in mutually normal directions.
Processing of survey data included the following main operations:
- Post-processing of flight GPS and IMU measurements;
- Post-processing of UltraCam-D images;
- Calibration of angle units for UltraCam-D and Rollei cameras exposition;
- Processing of LiDAR data and creation of 3D cloud model and digital elevation model;
- Orthorectification of UltraCam-D images;
- Creation of a textured 3D model using point clouds and oblique images.
The total project area is about 2,200 km2. It includes territory within the city limits (including urban territory), and non-urban areas or areas of industrial facilities adjacent to the city line. As a result, following output products have been created: digital topographic map 1:10,000; digital topographic map 1:2,000 (for a part of the territory); digital topographic map and orthophoto 1:1,000 (for a part of the territory); digital elevation model; oblique imagery; photorealistic 3D models of selected areas.
