ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001
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3 SPATIAL INFORMATION COLLECTING BY IDCS
It is known that mining subsidence can be expressed by two
means: spatial position (elevation of points) and attribute change
(the land use and land cover change caused by mining
subsidence). Spatial information is the basis of all studies,
especially in GIS applications.
Nowadays, spatial information about mining subsidence can be
captured from different means, including field surveying by
theodolite, level, and Total Station (TS), cubic measurement and
landscape reconstruction by photogrammetry and Remote
Sensing, deformation monitoring based on INSAR technique,
estimation by forecasting model, and dynamic monitoring by
GPS technique.
Nowadays, forecasting model and field surveying are the main
techniques used in practices, but each of them has inevitable
shortages. Forecasting model depends on the geological, mining
parameters and mechanical features of rock, and is variable with
external environment, and some assumptions are applied in the
model, so its precision is limited, even though different methods
and theories are used. Field surveying is time-consuming, high
cost and only results on some observing points can be
measured, and other points should be interpolated by
mathematical model, so the precision is not very high.
With the development of photogrammetry, GPS, and Remote
Sensing (RS), spatial information of subsiding land can be
collected by those techniques. Especially Digital
Photogrammetry System (DPS), GPS combined with GIS can be
used to realize the integration of information collecting,
processing, 3D simulation and representation and spatial
analysis in an uniform system.
3.1 DPS and its application
In recent years, DPS has become one of the most important
means to get spatial information about terrain, landscape,
building and other entities, and some software such as VirtuoZo
can be used. Fig.3 is the flow of DPS to spatial information
collecting of subsiding land.
Because subsiding land is low in middle and high at edge, it is
convenient to do the fieldwork of photogrammetry, and some
work had been done in this field. The further direction is to input
the images into GIS, process them by professional modules
compute spatial information and represent the results by DEM
and contour.
3.2 GPS and its application
With its advantages of round-the-clock observation, high
automation, 3D information collection simultaneously, easy work
Fig.3 Spatial information collecting and processing by DPS
and so on, GPS technique has got more and more applications
in surveying, deformation monitoring and navigation. GPS
applications to mining areas have already got some progress,
and one of them is to monitoring and surveying subsiding land
including its borders and 3D shapes. In GPS applications to
subsidence monitoring, the most important issue is
determination of elevation and differences in elevation. In order
to use GPS to subsiding land monitoring, two schemes can be
used, which are illustrated by Fig.4 and Fig.5.
We can know that the Scheme in Fig.4 is based on height
interpolation and transformation between geodetic and normal
height and the key is abnormal height, and scheme in Fig.5 is
take the difference in geodetic height as subsidence quantity
directly. It proved to effective to use each of the two schemes.
GPS observing data should be process by special software
before spatial information is got. Two methods can be used to
input GPS information into GIS, one is inputting 3D coordinates,
that is X, Y and Z of each points computed by special software to
GIS and the other is to develop GPS data processing module
inGIS and raw observing data is input. At present, the former
method is used mainly, but with the development of integration
of GPS and GIS, the latter would be more convenient.
3.3 Integrated data collecting system and its applications
Several methods can be used to collect spatial information of
subsiding land and each has its own advantages and shortages,
so a useful choice is to set up an Integrated Data Collecting
System (IDCS) to use the most effective methods for different
