Friday, 16 March 2012

4D GIS

I received many feedbacks for the two posts about gvSIG 3D (gvSIG 3D and gvSIG with SfM data). I think the most important thing about the possibility to import 3D data in gvSIG with the obj format is that in this way we can import the two main kind of 3D data normally we have in archaeology: 
  1. 3D documentation
  2. 3D reconstruction
Considering as fourth dimension for this data the value t (time), so that each single point has three spatial dimension (x,y,z) and a temporal dimension (t), we see that in archaeology the concept of documentation and reconstruction are very different. 

In this short movie, in which I registered in gvSIG 3D the two 3D dataset I used for the test, it is possible to understand better this difference.



The burial is a 3D documentation, done in March 2010 and recording the situation in which we found the archaeological evidence after its deposition and all the post-depositional  alterations. From a 4D point of view its time value (t) is March 2010 and it is connected with a single event: the discovery of the burial, which archaeologically can be considered as the last event in the "micro history" of the object.
The church is a 3D reconstruction which hypothetically describes the building in one  of its "life cycle" stages, after its initial construction, and, more precisely, during the XIX century. From a 4D point of view its time value (t) is XIX century and it is connected with a period (after the architectural changes of the XVIII century and before the minor building modifications of the XX century). In short it is a hypothetical reconstruction of one of the post-depositional alterations of the object. 

Another difference between this two kind of 3D data regards the techniques with which the 3D model are done. The burial was documented with Structure from Motion and Image-Based Modeling techniques (Python Photogrammetry toolbox), while the church was reconstructed with a 3D modeler (Blender).

The final difference is related with the normal work-flow of an archaeological project: the 3D documentation is done during one of the first stages, consisting in the archaeological excavation, while the 3D reconstruction is done just at the end of the whole process, after analyzing all the collected data.

In other words the main news about gvSIG 3D, from an archaeological point of view, is the possibility to handle in a GIS 4D data (x,y,z,t), following the natural evolution in the discipline methodology. 
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