Monday, April 27, 2009

Can't use an atlas for geoinformation

Wikipedia defines an atlas as a collection of maps. Atlases were created to represent geographically distributed information on the Earth surface: physical geography, political geography, and any socioeconomics information for which the geographic distribution makes sense.

Atlases are also used in anatomy. They describe how the animals' organs are located into the bodies. The term atlas here is used by analogy to the geographical ones.

Anatomy atlases are often used in medical image processing, since they allow to introduce prior knowledge about the object of study in a convenient way. This way, spatial ontologies can be built to guide segmentation or classification algorithms. The relationships between different objects in the body are known and described in the atlas.

In the same way as anatomy (and as a consequence medical image processing) borrowed the term atlas from geographic information, remote sensing scientists have tried to get inspiration from medical imagery in the how prior information can be used for remote sensing scene analysis and interpretation.

In this context, atlases or ontologies have been developed in order to represent how the objects present in a remote sensing image are distributed and what are their mutual relationships.

Not surprisingly, there has not been a major break-trhough in remote sensing image analysis using this kind of technique.

In my opinion, this is due to the fact that the object of the study can contain much more variability in remote sensing than in medical imaging. For example, the spatial relationships between different parts of the brain are much less subject to variability than, for instance, the relationships between the buildings which make up an airport.

However, nearly any human operator, even not very much trained, can recognize an airport in a remote sensing image. Why?

Well, I guess that in anatomy, the spatial relationships are some kind of optimal solution to a problem which is posed in terms of functional relationship and species evolution. This is closely linked to morphogenesis.

The organization of geographic entities linked to anthropic activities is also the result of a solution of a problem posed in terms of functional relationship: the buildings of an airport must comply with a certain number of functional needs (access to planes, security regulations, etc.), but they are only a solution, not the optimal one. After all, these are solutions proposed by men, not by nature after several millions of years of evolution!