Senin, 16 Maret 2009

3D GIS and GeoEye-1 GeoStereo Imagery

The notion of "3D GIS" has been gaining momentum in the geospatial industry for a few years now.  Witness the recent seminar conducted by the Britsh Columbia URISA chapter: "The New Dimension in GIS - 3D Analysis".  If the topic interests you, abstracts and many of the full presentatiosns can be downloaded from the site.  A look at the topics shows an examination of digital cities, 3D models, BIM, LIDAR, digital orthophotos orthophotos and more.  The industry has been abuzz with the integration of GIS, photogrammetry, and remote sensing for some time now, but only recently have the data products and tools have matured to the point of making integrated 3D GIS applications a reality.

Satellite imagery providers that have stereo collection capabilities are a good example of the drive to generate 3D data products.  As I've commented previously, the lack of industry standards for photogrammetric metadata poses a challenge to offering stereo products - but this is changing with data vendors pushing stereo products forward and efforts at the OGC-level to drive standards. An interesting item from Matt Ball's summary of the recent ASPRS conference in Baltimore was the keynote presentation from John R.G. Townshend, "calling for the standardization of imagery metadata".

GeoEye packages their satellite imagery products in a few different categories: Geo, GeoProfessional, and GeoStereo.  As stated on the GeoStereo product page, "the RPC camera model supports block adjustment, three-dimensional stereo extraction, DEM generation, ortho-rectification, and other photogrammetric operations. "  

GeoEye-1 Stereo Imagery in LPS

The benefit of stereo imagery is the value-added geospatial information that can be derived from it.  The quote above relates three specific data products: digital orthophotos, terrain models, and 3D vector data (three-dimensional stereo extraction).  Digital orthophotos have become a standard component in base map data, and can be used for accuracy assessment (e.g. are the vector data layers complete and correct?), 2D vector digitizing and update, change detection, and a number of other applications.  Terrain data, which can be automatically generated, is a key component for orthophoto generation, and is useful for a wide variety of other applications as well. The other data product mentioned above is 3D vector data.  One of the major benefits of stereo imagery is the ability to measure objects in X, Y, and Z and collect 3D vector data.  Not only can the vector data be extracted in XYZ, but the objects can be accurately extruded down to the ground level.  This provides a 3D object that can then be attributed, textured, and then fed into a variety of applications.   

Since we recently received GeoEye-1 GeoStereo imagery for validation in LPS, I thought it would be worthwhile running through the workflow in LPS 9.3.1.  In the next post I will outline the workflow steps - with the right set of tools, developing the products outlined above is a very straightfword process!  

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