The system of modelling terrain on aerospace survey data

A.I.Alchinov, N.D.Beklemishev, V.B.Kekelidze, V.V.Kostin

V.A.Trapeznikov Institute of Control Sciences of RAS, Russia

The system has been developed for prompt computation and on-the-fly visualization of terrain models from aerospace photography data for purposes of navigation and moving objects guidance. Visualization is performed on basis of terrain model composed of detailed digital elevation model with orthophoto overlay; texture and quality of thus rendered images comply with that of photography source data, and the model computation can be performed automatically as well. The model applies for navigation and guidance tasks as follows: a) computer reproduction of an actual traversed path; b) route choice and guidance of a moving object using the visualized terrain model and the moving object simulator; c) navigation and guidance of a moving object by comparison of on-board terrain model calculated during the flight to the predetermined one.

 

The laboratory for Moving Objects Control Dataware of Russian Academy of Sciences Institute of Control Sciences has developed a system for prompt computation and visualization of terrain models from aerospace photography data. The system has control interface responsible for camera model movement with features of recording track data and repassing the route. Visualization is performed on basis of terrain model composed of detailed digital elevation model (DEM) with orthophoto overlay; texture and quality of thus rendered images comply with that of photography source data. The application stores data in specific hierarchical structures providing quick access that ensures rendering rate of tens frames per second. Computation and visualization area for terrain model can be nearly unlimited. In case source data contain any georeference to some particular Earth-bound coordinate system (i.e. global navigation satellite system coordinates of projection centers or terrain control points), all the data can be output in this coordinate system, otherwise processing is performed in a local coordinate system.

The system has advanced facilities for prompt computation of surface geometry and photoplans enabling relatively fast access to these data for visualization according to source images. Processing can be performed both manually and automatically. The system comprises many innovative solutions; some of them are patented in the Russian Federation.

 

In addition to permanent works on development and optimization of algorithms that enhance quality and speed of automatic processing and on improvement of user interface that increases efficiency of operators' labor, following lines of development of the system, qualitatively improving its features, can be pointed out:

1. Support of vector 3D objects with textures in visualization unit. In so doing, vector 3D objects can be loaded from external sources in standard 3D formats, e.g. 3dmax, or digitized in stereo by operator on basis of calculated geometrical projection model. Research into automatic recognition of certain classes of 3D objects deserves consideration as well.

2. Support of usable and informative display of text markers and comments on terrain in visualization unit.

3. Consideration of radar survey data as auxiliary input during terrain calculation. Such consideration can enhance quality and precision of resulting terrain model.

 

Calculated terrain model including DEM, orthophoto and general terrain rendering from different points can be used for navigation and guidance of moving vehicles, in automatic process mode as well. Following cases should be mentioned:

1)                  A vehicle while moving can record its trajectory using global navigation satellite system receiver and other on-board means for determining absolute coordinates. Saved route can be later visualized with the help of computer.

2)                  The system can be coupled with a simulator of some particular flying or moving object. Using such a frame an operator can (subject to other additional general requirements) choose an optimal route for machine movement over the given terrain model, allowing, for example, high precision access to a prescribed point. This route can be saved, and then its coordinates and other parameters can be used when actually moving along the route in order to accomplish control and guidance tasks, in automatic mode as well.

3)                  Given sufficient computational facilities, terrain model can be calculated immediately at the time of movement according to the data of on-board photography. Comparing this model with the predetermined one, navigation and guidance technologies can be developed. It will be noted that such navigation and guidance technologies can be the only available option for a machine, failing possibility of using wireless beacons, global navigation satellite system, astroorientation system or other conventional technologies.