In this paper, we try to build a mechanism or a cycle to collect
real-time data form VGI to SDI, in turn SDI public the verified
data to VGI. The mechanism or cycle includes collecting VGI
data, preprocessing data, matching the homonymous elements
between VGI and SDI vector data, detecting changes, verifying
the credibility of the changes, updating SDI database, updating
the products to end-users. The paper is organized as follows,
section 2 briefly surveys the issues associated with the
utilisation of volunteered spatial information in SDI; section 3
looks at the difficulties posed by the above issues in section 1
and give a framework of the mechanism or cycle, describes he
mechanism or cycle itself in details, section 4 take the mapping
departments of china as an example ‚discusses the problem of
the mechanism or cycle adopting in SDI; section 5 gives the
conclusions and future directions of research.
2. PROBLEMS AND CHALLENGE OF VGI
There are a lot of issues that may exists in the mechanism of
VGI in support of SDI updating, such as data quality, data
structure, data differentiation, data copyright, data confidential
and privacy and so on. Firstly , data quality depends on the way
of collecting data in VGI , the users use mobile phone or on-
board GPS to record the GPS track, draw the outlines of
geographic elements on remote sensing image or aerial photos
to acquire vector data, add attribute information according to
their own experiences, upload audio and pictures to
contribution data. There are many problems in the contributed
data quality. The civil GPS do not have enough accuracy
compared to professional GPS equipments; the feature drew by
users without professional training may not fully meet the
requirements of the professional departments, which is difficult
to directly used by the professional surveying and mapping
database; professional surveying and mapping data pay
attentions on the standardization of attribute data, such as word
length and data type, conversely in VGI operating environment
which only has established some standard to limit the
modification behaviour; the semantic ambiguity brought by the
different opinions of cognitive limitations from users to collect
attribute information. If using VGI data to in the support of
updating professional data in surveying and mapping
departments, the new rules and standards should be built for
data preprocessing, filter and conversion to meet the standards
of professional surveying and mapping departments. Secondly,
in VGI platform the same features edited by many users may
cause geometry objects with mass points, which brought more
difficulties in a wide range of data acquisition and inquires. For
instance, if the inquiries or requests over 0.25 square degrees of
data by users will be refused server in OpenStreetMap. The
massive geometry objects not only set up a barrier to the inquiry
and request, but also obstruct the updating and modification, so
how to build new, flexible and efficient data types to satisfy
the professional departments become a big issue. Thirdly, for
the differences of informationization level in different areas and
the distribution of VGI users, the differentiation of VGI
information becomes a problem. Usually, in densely populated
areas VGI data is intensive, wherever the data in the most
inaccessible areas is sparse. Beyond that, there is also data
copyright, data security and privacy etc. This paper doesn't
discuss in this section.
quality
differentiation
copyright
confidential
privacy
Figure 1. The problems of VGI data
3. FRAMEWORK OF THE MECHANISM
Based on the above discussion in section 2, aiming at settling
the problem that how to utilise VGI data to update professional
surveying and mapping department database timely and in turn
professional department publics the enhanced data to VGI
platform, this paper present a mechanism as organic cycle to
support the requirement. This mechanism emphasizes the
thought that *data from users, to users", the users provide more
real-time data by various ways, such as GPS, drawing the
features of geographic objects etc. to SDI, SDI verify the
validation of data and release the verified data to the user,
which promote each other and help to improve the efficiency of
data updating. Firstly, we give the current methods for VGI data
collection and preprocessing; secondly according to the
characteristics of VGI data, discuss the matching algorithms for
point, line, polygon between VGI and SDI vector data to detect
the changes; thirdly, provide automatic SDI database linkage
updating rules; forth, release the real-time and verified data to
VGI.
b | verified data
Figure 2. Framework of the mechanism
3.1 The methods of data collection and preprocessing
Nowadays, we make a general survey of current VGI websites,
VGI data is mainly achieved by the following kinds: GPS track
or point of interest recorded by handheld or on-board GPS; the
outlines of geometry object for points, lines and polygons drew
on online high resolution remote sensing image or aerial photos;
attribute information based on the user's cognition; the texts,
images, audios and videos which contain position information
etc.. According to the nature of data, it can be divided into
graphics data and semantic data, graphics data includes GPS
track, POI and the outlines of geometry objects; semantic data
includes attribute information and related text, images and
video etc. Because there is a great gap between VGI data
416
acquisition n
methods, VG
data quality; |
of geometry
standards of
the complexi
etc. So, if |
wants to harn
pretreatment
standards of |
in this section
At present,
Openstreetma
rules to restri
permissions, v
to judging th
format and fi»
and third-part
layer should t
first layer for
achieving reli:
by format co
topological r
consistent of
requirements c
3.2 The algo
The more im}
elements reco;
detecting the
project of Un
States census |
data map whic
adjust and iter:
the matching r
1988). Since
theoretical anc
matching. The
geometry, sen
indexes to fis
characteristics
provide an alg
globally; choos
each layer; c
homogenous e
threshold area.
department nec
method to colle
Figure 3.
