The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008
Figure 2. (a) A typical PDA ;( b) the 3D mouse; (c) regular
mouse with trolley; (d) stereo glasses and radiator
Undoubtedly, such kind of integration benefits the information
exchange and sharing between image interpretation indoors and
investigation in field, and thus evidently reducing the
complexity and redundancy in the traditional update process.
Besides, it brings much flexibility in the workflow adjustment
and optimization aspect, making a transition from the traditional
serial workflow to the more efficiently collateral mode. For
instance, after the data integration during which pre-warning
change analysis is carried out either through automatically
image based change detection or field exploration, the update
procedures can be flexibly adjusted and configured. Commonly,
image interpretation indoors finishes most of the geospatial data
collecting and editing work, which effectively releases the
labour intensity in field and shortens the whole update cycle;
besides, the work assigned to workers indoors and in field is no
longer rigorously divided as before. In the collateral working
mode, field workers are in double harness, on one hand, they
work in field with PDA; on the other hand, they can timely
download the field data recorded by PDA to the portable
computers taken with them, and then the field data is integrated
with the indoor data based on the functional modules installed
on the portable computers. As a result, the process of data
revision can be performed timely, which guarantees the
correctness and up-to-date state of the final results. Overall, the
operation mode of integration brings immense innovations to
traditional serial workflow, also considered to be an effective
exploration to the full digitized work tendency for field
validation and supplement in future.
2.2 Integration of multi-source information
Inferred from the essence of image-based GIS database update
described in the second chapter, data preparation is the
prerequisite step for update which refers to the projective
management and uniform process of various useful materials,
primarily including the existing DLG data and multi-resolution
multi-temporal image datasets, either spacebome or airborne,
either in single or in stereo; meanwhile, the multi-scale
topographic map and other thematic data from relevant areas
and etc are sometimes included as accessory. The purpose of
data preparation is to make multi-source data more efficient and
utilized for update.
Format transformation and data importation: the up-
to-date spatial images, the existing DLG and other information
to be used for update are in various data format. For geo-
referenced images, the format can be Geotiff, Tiff or BMP; for
DLG with the corresponding scale, which are stored with the
separate map sheet and named according to the map sheet
encoding standard, there also exist various formats such as
ESRI Shapefile, Arcinfo coverage, Arcinfo eOO, Geodatabase
and etc; for other materials like place name database and GPS-
collected road net also have specific formats. Data in different
formats are inconsistent in terms of organized structure, datum
and unit, so one of the most important missions for data
preparation is format transformation, where DLG in various
formats are uniformly transformed to the inner designed vector
format of the system; besides, DOM, DRG, DEM, etc. are also
integrated into the respective inner supported format, i.e. data is
homogenous in format within each dataset. The designed inner
formats here are compatible with the indoor working
environment in which the integrated vector and raster datasets
can be loaded and registered in convenience.
Block management: the image-based GIS database update
not only relies on the up-to-date orthoimages for registration,
collection and update, but also integrates photogrammetry with
GIS for DLG^ DEM, DOM and 3D Model update. With the
development of various airborne and spacebome imaging
sensors, block management is also regarded as an important
aspect for data preparation. Here, the fulfilment of block
management mainly includes organization of the block data,
generation of stereo models and seamless stereo orthoimage
pair (Wang 2004) as well as orthoimage in single mode. The
prepared block then is loaded to the indoor working
environment, and stereoscopic observation and update can be
carried out on the selected stereo models or stereo orthoimage
pair.
Data registration, fusion and change analysis: it is
commonly known that the image-based GIS database update is
interpreting change information from various geo-referenced
images, based on which the existing DLG is updated. Therefore,
data registration here primarily concerns about the registration
between different images, or between images and DLG.
Generally speaking, there are mainly two approaches for data
registration: one approach is adjusting the geo-reference
information of image dataset through semi-automatic human
interactions with multi-layer overlapping; the other routine is
much the same as image rectification, through automatic feature
extraction and matching of images and DLG, thus
accomplishing the data registration process finally. Besides,
spatial registration of multi-temporal or multi-sensor images is
required for many applications in remote sensing, such as
change detection, the construction of image mosaics, DEM
generation from stereo pairs and orthorectification. Once
registered, the images can be further fused or combined, in a
way that improves information extraction.
2.3 Integration of scheme throughout the update
process
For GIS data collection and update, it is a prerequisite work to
configure a comprehensive scheme. Theoretically, a scheme is a
database file which is preliminarily integrated with the indoor
working environment while the update performance is carried
out, actually there is no definite restricts for the type of the
database. All in all, the purpose of scheme configuration is
organizing various meta-information for GIS data update into
an open database. In summary, the update scheme mainly
constitutes the following contents: it firstly manifests the
hierarchical structure of the updated data, according to the
relevant industry standard; next, the scheme establishes the
corresponding relationships between the exiting GIS database
and the new one, such as the reference of old and new feature
code, the reference of old and new attribute field, etc. In
addition, the configured scheme includes the meta-information
of each category, layer and feature from the perspective of
