|
|
|
Integrated Remote Sensing and GIS for Natural Resources Management
|
The development of national topographic and cartographic data bases for geographical information system (GIS)implementation in Malaysia
Data acquisition and editing
Primarily data acquisition is performed utilizing photogram metric and digitizing technique in the CAPS and CARDS, while data editing is performed in the CACS units.
- Data Acquisition - Photogrammetric Technique
Aerial photographs are the basic data source of data input. Data acquisition utilizing photogrammetric techniques involves two major steps. The first step is the so-called Aerial Triangulation by which supplement by which supplemental mapping controls are provided. The second step is concerned with the actual data collection of features from aerial photographs, referred to as the process of stereo compilation.
- Aerial Triangulation
Aerial triangulation utilizes a semi-analytical process, which comprises the following procedures: -
- Identification of the available ground and supplemental control points in the aerial photographs.
- Transferring of the control points on photographic materials utilizing WILD PUG4 point transfer device.
- Photo coordinates measurements, utilizing stereo metrograph fitted with rotary encoders and stereo track digitizing system.
- Refinement and compensation for systematic errors and final preparation for the data processing and adjustments utilizing stereo track Digitizing system (model formation and connection).
- Control data processing and adjustment, which includes the analytical photogrammetric processing to determine the coordinates of the supplemental control as well as other photograpmmetric parameters utilizing PAT-MR block adjustment program.
- Stereo Compilation
Stereo compilation involves the digitization of topographic features at the scale of 1:25,000 utilizing Kern PG2 and Wild B8 stereo plotters, fitted with rotary encoders and stereo track digitizing system. The procedures are as follows :
- Stereo model set up by applying the photogram metric process of inner, relative and absolute orientation, utilizing stereo track digitizing system which run on microcomputer PC-XT (IBM Compatible).
- Each feature digitized is coded in accordance to the Malaysian appropriate level in the data base.
- Digital data files are produced for each stereo model containing coded coordinates adapt for both planimetric and/or topographic features.
- This data files are then transmitted to VAX mainframe computer which support all the interactive graphic system for editing and final preparation processes.Verification plot utilizing calcomp plotter is produced for monitoring and verifying the collected data accurately defines the map features.
- Adjacent model are then joined, edited and clipped on VeRa 360 workstations utilizing GINIS 300 (Interactive editing and digitizing software) to produce clean digital.
- Field completion plots consisting of a composite plot and various layers such as back, road, color, height, name and traverse tracings, for field validation by the topographic division.
- Data Acquisition - Digitizing Technique
Digitizing techniques involves two major processes, that is, automatic and manual digitizing. In automatic digitizing, digital data are collected utilizing the raster scanner (Kartoscan), while in manual digitizing map features are traced on a digitizer table with tracking device.
- Automatic Digitization (Raster Scanning)
In automatic digitizing, the Kartoscan raster scanner is used to convert graphic data into digital data in raster format. This raster data structure takes the shape of a metric of one and zero element representing the black and white areas on the map respectively.
- Raster data are concerted into vector form by a vectorising program (Raster-to-vector conversion software) utilizing several options provided by the softare depending upon the type of data to be processed.
- In cases where contour lines are originally in imperial unit, conversion to metric unit is necessary. This is done by first tagging the original contour values using VeRa 540 workstations and subsequently interpolated by menus of the Raster Digital Terrain Model (RDTM) package to produce new contour liens in metric.
- The vectorized data are then edited and structured according to the Malaysian Standard Digital Feature Code utilizing GINIS (Graphic Interactive Information System) of VeRa 360 workstations.
- Field completion plots consisting of a composite and various layers such as black, road, color, height, name and traverse tracings are prepared for field validation.
- Manual Digitization
Manual digitizing utilizing Computer Aided Digitizing package (CADIG) on VeRa 110 workstations is carried out to supplement data collected through scanning. The digitization procedures are as follows: -
- Digitization is performed by simply moving the tracking device over each point to be recorded. Upon the operator, command, the planimetric coordinates of each point are sensed and recorded automatically.
- The process continues to digitize the necessary points forming vectors (consisting of a pair of points) and lines (consisting of a sequence of vectors). Features are digitized according to their appropriate levels.
- Data editing - Cartographic Enhancement
Map data collected from CAPS and CARDS and subsequently from field completion from the core of the raw map database. The raw database is further restructured into their appropriate levels according to Malaysian Standard Feature codes and eventually edge-matched to connect border liens. This then forms the accurate maps base, which will be used for subsequent data retrieval and exchange.
For the production of printed maps, the topographic maps obtained above are further enhanced and generalized, whenever necessary to produce printed maps with color separations for map production. The enhanced maps will form a set of cartographic database only for the purpose of map production. The color separations are then over layed to form a complete printed map. The editing procedures are as follows: -
- Field data are added to the cartographic data files from CAPS and CARDS, which will be interactively edited for final cartographic output.
- The additional information is added trough manual digitizing utilizing CADIG and latter interactively edited.
- Interactive editing utilizing GINIS on VeRa 544/540 involves error detection and corrections of data and the upgrading of data files. The standard editing functions include joining of liens, clipping and manipulations of text and symbol descriptions, some of which will involve moving locations, changing size and rotations.
- The data processing will then follow for the manipulations of data for input into the final display unit. Data manipulations include the specific task of data reformatting, metric transformations, generalizations, exaggerations and data reductions.
- Cartographic data files at the scale of 1:25,000 and 1:50,000 in various layers such as black, blue, green, red, brown, X-mask and Mask are then created for plotting on high precision flat-bed plotter in preparation for the final printing.
|
|
|
|
|
|
|
