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23.2 Data recording equipments: Digital camera was used
to record the condition of the forest stands, land-use status, and
survey marks. Hand-held PDA (personal digital assistant) was
used to record field data including work logs, sample plot data,
and imageries of the study area. Notebook computer was used
for processing measured data and adjustment computation. The
notebook computer was also used to produce maps that can be
used for field survey.
23.3 Computer equipments: Major computer hardware
equipments used in this study included desktop computers,
notebook computers, PDA, large size inkjet plotters, and colour
laser printers. A computer aided drawing software, Microstation,
was used for map editing and drawing. To build a geographic
information system for the protection forests, ESRI GIS
software ArcGIS and ArcView GIS were used. In addition,
Microsoft Visual Basic was used to maintain the spatial
database, and ArcIMS was used to build a web-based
geographic information system.
3. METHODS
3.1 Data preparation
The original protection forest maps had a coordinate system
differing from all the other maps, and the associated parcel
records were outdated. Current cadastral data and maps were
used to compare with existing data and maps, and erroneous
data were either removed or updated. The maps were then
digitized using Arcedit, and parcel records were entered using a
software written in Microsoft Visual Basic. The topographic
maps, created using Microstation, have 36 layers, among them
the layers of roads, buildings, contour lines, and streams were
extracted using a program written in MDL (Microstation
Development Language). These layers were then converted into
ArcGIS coverages. +
The cadastral records and digital cadastral maps were provided
by the Taipei City government, however, the data format was
not compatible with ArcGIS. Therefore, computer programs
written in C programming language and AML (Arc Macro
Language) were developed to convert these data into ArcGIS
spatial database, and attribute data entry and maintenance was
done through software tools developed using Microsoft Visual
Basic.
The maps and imageries used in this study were from different
sources, and often had different scales and accuracy level. To
have a consistent coordinate system, all the maps and imageries
were georeferenced with the aids of field survey data and
available ancillary data.
3.2 Field survey
32.1 Mapping standards: One of the goals of protection
forest revision was to survey the boundary of these forests and
update related parcel records to reflect the current ownership
information. Traditionally forest survey does not require very
high accuracy. The protection forests of the Taipei City are
intermixed with private-owned lands. Consequently the
accuracy of survey results may have great influence on the
interests of the private land owners due to very high property
values. Therefore, the boundary survey was controlled to
conform to the cadastral survey standard.
343
3.2.2 Protection forest maps: In this study, the protection
forest boundary survey is a type of retracement survey, i.e., the
surveying was aimed to recover and monument or mark
boundary lines of the forestland (Wolf and Ghilani, 2002).
Therefore, obtaining accurate coordinate for the boundary
points is essential to this study.
The old protection forests maps were prepared nearly a hundred
years ago. The accuracy of these old maps did not conform to
the current mapping standard and hence revision to these maps
were needed. Prior to field survey, satellite images, aerial
photographs, orthoimages, photo base maps, topographic maps,
and cadastral maps were used to compare with the old
protection forest maps. After a series of parcel records checking,
digitization, map editing, image registration, georeferencing,
and coordinate transformation processes, new protection forest
maps in digital format were created. For field survey, 1/1000
protection maps overlaid with topographic maps was plotted on
papers, which were used as reference maps for locating sample
plots and other purposes.
3.2.3 Surveying procedures: The first step was to measure
control points for the study area. In addition to the control
points of cadastral survey and satellite oriented control points
obtained from the Satellite Survey Center, this study employed
real-time kinematic (RTK) procedure using Leica GPS system
to measure control points. Due to rugged terrain and dense
forest canopy, it was difficult to obtain good GPS fixes in some
areas. When necessary, traversing survey procedures were
employed to ensure appropriate accuracy level of the control
points.
Detail survey was employed using Leica total stations. The X, Y
coordinates of each corner of the protection forest boundary
were downloaded to the total stations and relevant information
were also downloaded in PDA or notebook computer when
surveying the forests. Pictures of all land marks were taken
using digital camera, and the accuracy level as well as methods
used to measure the control points were recorded.
3.2.4 Forest stand investigation: Since establishment of the
protections forest, the natural environment had changed during
these decades, and the socio-economic changes also resulted in
impacts on the protection forests. The status of the protection
forests was thoroughly checked in this study. Aerial photos,
orthoimages, and topographic maps were used to analyze the
land-use status, and sample plots were selected to investigate
the vegetation as well as soil characteristics of the forest stands.
Each tree in the sample plots was tagged, and the species, height,
DBH (diameter at breast height) was recorded. In addition, the
center of each sample plot was measured using total station.
3.3 Protection forest management system
To facilitate management of the protection forests, a spatial
database containing various maps, imageries, field survey data,
and cadastral records was built, and a geographic information
system was developed for this study. The database was
maintained using a software developed in Microsoft Visual
Basic, and spatial analysis, inquiries, and presentations of maps
were employed using ArcView GIS. ArcView Avenue
programming language was used to develop extension tools that
can customize the user interface and automate analysis
procedures. Figure 3 depicts the architecture of the protection
forest management system.
