The Production of Photo Base Map in Taiwan
Jih-cheng RU
Keywords: Aerial Photo, Photo Base Map, Orthophoto Mapping Method
Director, Agricultural and Forestry Aerial Survey Institute No 61-3, Chao-chou Street, Taipei, Taiwan Tel: (886)-2-23931837 Fax: (886)-2-23931870 E-mail: nn240918@ms19.hinet.net TAIWAN Abstract: In July 1975, the Executive Yuan (Cabinet) approved a project for producing large-scale photo base maps covering all of Taiwan. The mapping project is sponsored by the Ministry of Interior with the assistance of Council of Agriculture, but the actual mapping work is executed by the Agricultural and Forestry Aerial Survey Institute, Taiwan Forestry Bureau. The photo base maps were made from aerial photos through the orthophoto mapping method. At the end of 1999, the completed photo base maps can be divided into two systems. The analog mapping system with a total of 15,160 sheets included:(1) Base maps of the first edition 3,773 sheets, the second edition 2,000 sheets, and the third edition 2,400 sheets. (2) Forest maps of national forest 37 working circles 3,731 sheets. (3) Coastal area maps 3,256 sheets. The digital mapping system with a total of 1,580 sheets included:(1) Base maps 856 sheets. (2) Forest maps 604 sheets. (3) Others 120 sheets . These completed photo base maps are widely used by the people of all sectors and has won nation-wide acclamation because of their delicacy and accuracy. Besides, the photomaps provided more and clear ground features. It has made an outstanding contributions to the promotion of aerial survey mapping work and national economic development in Taiwan. 1. Preface The land surveying works of Taiwan are divided into three parts:(1) Revision of basic control points. (2) Production of photo base maps in Taiwan areas. (3) Resurveying of cadastral maps. In order to meet the needs of national economic reconstruction, The Agricultural and Forestry Aerial Survey Institute has been actively developing its aerial survey and remote sensing business. Now, The Institute possesses two aerial survey airplanes, digital mapping and resource inventory instruments, as well as the most experienced technicians to perform the aerial photography, mapping and resource inventory works. 2. Photo Base Map 2.1 Definition The digital photo base map is storing the spatial data of the global surface in the computer by means of digital form. The geometric data of the point, line, and area on the base map are expressed by the coordinate system. It is enable to provide the GIS applications. 2.2 Theory of Mapping central projection photo®differential rectification®orthographic projection photo 2.3 Map Accuracy
The map projection is based on the Two Degree Zone Transverse Mercator Projection. Central meridian 121° East Longitude, y coordinate shift to west 250,000 m., scale ratio of central meridian is 0.9999. 3.1 TWD 67 The Geodetic Reference System determined by the International Association of Geodesy and International Geophysical Union in 1967 was used for the coordinate calculation of the Taiwan photo base map. The data are as follows: Earth ellipsoid parameters : long radius a = 6,378,160 m short radius b = 6,356,774.7192 m flattening f = (a-b)/a = 1/298.25 Geodetic datum : based on the first order triangulation point named Fu-tse-shan. Longitude 120°58'25.975" Latitude 23°58'32.340" The azimuth to Tou-chi-shan = 323°57'23.135" Elevation datum : Taiwan Island based on the mean sea level of Kee-lung. Pescadores based on the mean sea level of Ma-kung. 3.2 TWD 97 In 1997, the Ministry of Interior announced the TWD 97 based on the determinations of International Association of Geodesy and International Geophysical Union in 1997. The data are as follows : Earth ellipsoid parameters : long radius a = 6,378,137 m short radius b = 6,356,752.31414 m flattening f = (a-b)/a = 1/298.25722210 GPS elevation survey : The elevation got from GPS survey is the height of ellipsoid. It should be deducted the geoid undulations to obtain the orthometric height. 4. Photo Base Map Production 4.1 Analog Mapping System From the fiscal year 1976 to 1999, the analog photomap production reached a total of 15,160 sheets. The details are as follows :
4.2 Digital Mapping System From the fiscal year 1995 to 1999, the digital photomap production was 1,580 sheets. The details are as follows :
5. Digital Mapping Procedures 5.1 Flight Plan
Prior to aerial photography, the ground targets must be placed on the control points in the areas to be photographed. The white rectangular plastic sheets are laid out around each control point to form a landmark in the shape of a cross or the letter Y or T. This will facilitate the identification of the location of the control points to be shown on the photographs. 5.3 Aerial Photography Aerial photography is implemented by the Agricultural and Forestry Aerial Survey Institute in cooperation with the Aeronautic Team of the Ministry of Communication. Two aircrafts, Super King Air Beechcraft 200 and Beechcraft 350 with GPS navigation are used to take the aerial photographs for mapping purposes. The camera used are Zeiss RMK TOP series, focus 15/23 and 30/23. The flying crew consists of a pilot, a copilot, a cameraman, a supervisor and a mechanician. 5.4 Photo Processing Black/White Aerial Film Processor and Color Aerial Film Processor are used for photo processing. 5.5 Ground Control Survey There are two ground control survey systems. One is horizontal and the other is vertical. Trimble SSI and Trimble 4700 are used for the horizontal control survey and the Wild 2002A digital level is used for the elevation surveys based on the benchmarks on the known elevation point. 5.6 Photo Scanning There are two instruments employed for digital photo scanning . One is Photogrammetric Workstation (PS-1) used for individual films, resolution ranges from 7.5, 15, 22.5, 30, 60, 120, 240 micron. The other is Photogrammetric Workstation (PS-TD) used for both roll films and individual films, resolution ranges from 7, 14, 21, 28, 56, 112, 224 micron. 5.7 DTM Recording Ground DTM = 40m ×40m or 20m ×20m by manual Cover DTM = 9m ×9m by automatic Match-T Program 5.8 Measurements and Triangulation Aerial triangulation is a triangulation survey based on aerial photographs to minimize ground survey work. Each aerial triangulation block consists of about 200 maps. The control points along the boundaries of the triangulation block are GPS surveyed, but the control points inside the block are measured from photographs. With the aid of a computer---Zeiss C-100 Planicomp Analytical Steroplotter, the PAT-M-43 program is used for aerial triangulation computation. All the measurements on aerial photographs are adjusted and tied to the ground coordinates. 5.9 Contour Line Plotting Zeiss P33/PC Digital Analytical Stereoplotter is used for the contour line; break line; hydrograph and spot height plotting. 5.10 Orthophoto Production The Intergraph ImageStation is employed for contour lines plotting and orthophoto production. The orthophotographs are rectified and printed based on the digital terrain data measured from the stereo model. 5.11 Field Photo Identification The orthophotos are field identified by the field team to add the names of places, buildings, administrative boundaries, road categories and numbers, landmarks, species of forest, crops and so forth. 5.12 Map Manuscript Compilation The compilers are checking orthophotos and contours to ensure that are matched properly. The map corners, map borders and grids are then plotted on the orthophotos and annotations are made on the overlay of orthophotos. 5.13 Field Editing In addition to examination at each working stages, one-tenth of the completed photomaps are selected for field editing to check if the position and elevation of ground features shown on maps meet a standard map practices, and whether the annotations and features are correct. 5.14 Drafting The maps are drafted on different coverage's such as the contour line layer, annotation layer, image layer and so forth. The negatives of composite map film are made through the MapSetter 5000. 5.15 Photo Map Printing The Gordon contact printer is used for the black and white photomap printing. The color map printing is carried out by the 401 mapping factory, Combine Service Force. 6 Map Distributions and Utilization All the finished photomaps are stored and saled by the Agricultural and Forestry Aerial Survey Institute upon request. The uses of photo base maps include :
In order to meet the tendency of digital mapping system, the Institute purchased the advanced aerial survey airplane with GPS navigation and RMK TOP aerial cameras, digital mapping instruments year by year. From the trial to mass production, it is really a journey to undergo all the hardships. At present, 15,160 sheets of analog photomaps and 1,580 sheets of digital photomaps have been completed. These completed photo base maps are widely used by the people of all sectors and have won nation-wide acclamation because of their delicacy and accuracy. It has made an outstanding contributions to the promotion of photomap production and national economic development in Taiwan. References :
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