ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001
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Fig.4 GPS technique to collect spatial information
Fig.5 GPS technique to monitor the subsidence
situations. IDCS has interface with each methods and can
process their raw observing data, and can provide GIS with
processed results by uniform format, generally the set of 3D
coordinates (X, Y, Z) of all observed points. Fig 6 is the structure
of IDCS.
With the IDCS, we can get the 3D information used for
simulation and representation of subsiding land.
4 3D DATA STRUCTURE
3D data structure is the basis of simulation and representation.
We have already given some discussions on 3D data structures
used to mines taking into account of properties and applications
in mines. Here we would propose some useful data structure for
representation subsiding land.
Fig.6 the formation and structure of IDCS
4.1 Surface Representation Using TIN and DEM
Subsiding land can be simulated by two means: one is
expressing the land surface according to elevation of every
points, and the other is simulating the dynamic process of mining
subsidence including deformation of land surface and movement
of rock from real 3D space. For the former, TIN and DEM can be
used, and integrated data structure for the latter.
Though TIN and DEM are not a real 3D representation, they are
used widely to represent the surface by 2.5D because the
algorithm is simple, data is easy to organize and collect, and use
is convenient. By (X, Y, Z) of all the points collected by IDCS,
TIN and DEM can be generated easily by GIS software, and
they can be transformed with contour and each other. Based on
DEM, some simple measurement and computation can be done.
4.2 3D Simulations Using 3D Integrated Data Structure
For complex simulation of mining subsidence, none of the data
structure can be used effectively and 3D integrated data
structure is necessary. According to the features of mining
subsidence, two integrated data structures were proposed as
follows.
4.2.1 Integrated data structure of 3D Raster and DEM
3D raster or Octree is used to represent the rock, coal seam and
goaf after mining, and land surface is expressed by DEM or TIN.
Firstly, the deformation and movement of land surface, rock and
goaf is computed, and then the 3D cell is marked according to
the generation rule of Octree. Octree and TIN are overlapped
according to spatial coordinates of some control points In this
scheme, the position and movement of rock should be computed
by spatial model and perhaps it is not precise enough.
4.2.2 Integrated data structure of 3D vector, Octree and TIN
The goaf by mining often is expressed by 3D vector data
structure because it can be viewed as a regular 3D space
composed by vertex, line, arc and face. The rock over goaf is
represented with Octree and the movement of each voxel can be
computed by spatial model, and the subsiding land surface is
represented by DEM or TIN. These three different data