The Production of Photo Base Map in Taiwan
Jih-cheng Ru
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
Keywords: Aerial Photo, Photo Base Map, Orthophoto Mapping Method
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 differences of x and y coordinates between the map and ground should be < 0.5 mm on the map.
- The differences of z value between the map and ground should be < 1/4 of the contour line interval.
- The shift of contour line should be < 1/3 of the contour line intervals in the flat land below 15 degree and < 1/2 of the contour line intervals in the slope land over 15 degree.
- The accuracy of digital terrain model is the same as the regulated contour line shifting.
3. Map Projection and Coordinates System
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.
