The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008
this paper we store the data block by block divided by regular
regions. The adjacent regions store the common vertexes and
triangular meshes as virtual vertexes and edges. Every block has
its serial number. Then we can evoke the data stored in the
RDBMS through the index of the serial number. These could
build a more efficient database based on the triangulated
irregular network model and will be helpful for the integration
of the multi-scaled DBMS.
Quaternary Triangular Mesh (QTM for short) is a proper
strategy to store, index and visualize the data. The surface of the
earth can be divided and subdivided by the triangular mesh as
the following Fig (Figure 2 and Figure 3).
Figure2. The Global Division and Subdivision of the triangular
mesh
Figure3. The Hierarchical Subdivision of the triangular mesh
According to the approach of global division and subdivision
above, the data of the QTM method can be organized as the
Figure 4 illustrates. The left figure is when the direction of the
triangular mesh on the ellipsoidal is up while the right one is the
opposite. So every block has it own index.
Figure4. Data organization based on the hierarchical subdivision
4 INTEGRATION AND UPDATE
Due to the storage strategy above, the data is stored in the
DBMS block by block. So when it comes to the visualization, a
logical seamless database could be formed including the
geometry information and property information. Because the
adjacent regions store the common vertexes and triangular
meshes as virtual vertexes and edges, we can use these virtual
vertexes and edges with the divide and conquer algorithm to
finish the integration between the adjacent regions.
Figure 5 illustrates a case.
A and B are the TIN-DEM products used to integrate a seamless
TIN. A1/B8, A7/B1, A2/B9, A6/B4, A3/B10, A4/B11, A5/B12
are the common vertexes of the two blocks. When the any one
of them is first chosen, the other one will search the common
vertexes and edges and find the polygon that consists of these
common vertexes and edges. In the polygon it will use LOP to
optimize the triangular meshes. Then the integrated TIN is
generated.
Figure5. Integration between two regions
We can build the pyramid of TIN-DEM automatically by
selecting the sample points at certain grade, so are the layers of
existing multi-scale seamless TIN DEMs. Thus, the update of
the database can be finished in the large scale TIN-DEM. The
other scale TIN-DEMs could update correspondingly. When
some new geographical feature points or edges are appended, it
uses the incremental algorithm to update of the data.
5 EXPERIMENT AND CONCLUSIONS
There is an experiment to test the strategy. The proposed
strategy was implemented in C++ language on Windows XP
operation system platform. Figure 6 is the data that selected to
construct the TIN. Figure 7 shows the constructed triangular
meshes. Figure 8 is the visualization system base on the
strategy.