DEVELOPMENT OF DIGITAL ORTHOPHOTO MAPPING 
Peter Y. Hsieh 
Vice President 
Time Aerial Surveys Co., Ltd. 
Taipei, Taiwan 
Commission IV, Working Group 4 
KEY WORDS: Orthoimage, Rectification, Mosaic, Scanner, Digitization, Softcopy, Production. 
ABSTRACT 
As Computers become more and more powerful, mapping tools for the 21st century are undergoing tremendous 
changes. With the benefit of today's computer technology, digital photogrammetry is replacing traditional analytical 
means as softcopy photogrammetric workstations become more and more commercially available in the surveying and 
mapping industries. The major features of the workstations are the use of digital images and the performance of 
mathematical modelling by automated computations in photogrammetric applications. With this tool non- 
photogrammetrists can also do photogrammetric work efficiently. Softcopy photogrammetry can now perform most 
photogrammetric tasks at a throughput and accuracy either better or at least equal to traditional analytical tools and 
its potential is unlimited. 
Time Aerial Surveys Company (TASC) has recently completed two (2) projects using these new technologies. One 
project was to produce fifty (bO) basemaps in digital orthophoto format for the City of Tai-Chung while the other was 
to produce color orthophoto maps of Tai-Chung Harbor. Both projects, involved the latest digital photogrammetric 
technique, are the first of its kind in Taiwan. 
This paper describes the entire digital photogrammetry workflow from image scanning to data compression to 
DTM/feature extraction to orthophoto production. This paper also highlights the challenges that TASC has faced as 
to how the best results could be achieved economically with limited resources. 
INTRODUCTION 
In the past forty (40) years, the development of Project | - Basemaps 
photogrammetry has gone through rapid changes from 
ancient analog mapping tools to modern analytical The first project, sponsored by the Ministry of Interior, 
. stereoplotters, and to today's digital photogrammetric calls for a production of fifty digital orthophoto basemaps 
workstations. In 1995, Time Aerial Surveys Company at 1:5000 scale covering the entire metropolitan area of 
successfully completed two (2) orthophoto mapping the City of Tai-Chung. Funds were granted for 
projects, both in digital format, using these new implementing this project on a pilot basis due to a 
technologies. One project was to produce fifty (50) transition from the traditional analog to digital 
black-and-white (B&W) photo basemaps covering the orthophotos. 
350 km? of the City of Tai-Chung while the other was to 
produce color photo maps covering the 160 km? of Tai- Background. Originally, a total of 3,773 photo basemaps 
Chung Harbor. Both projects, involved the latest digital covering the 35,981 km? of the entire island of Taiwan 
photogrammetric technique, are the first of its kind in were established over a seven year period since 1975. 
Taiwan. The workflow starts from image scanning of Of which, 3209 maps are in 1:5000 scale for areas with 
aerial photos, to aerotriangulation, to digital terrain model elevations below 1,000 m while the rest 564 maps are 
(DTM) data recording, to orthophoto rectifications. The in 1:10000 scale for mountainous areas with elevations 
state-of-the-art facilities employed by TASC include 1) above 1,000 m. These maps are being updated every 
Intergraph-Zeiss PS1 scanner for image scanning at a five years using analog means until now. The orthophoto 
resolution of 22.5 um; 2) Intergraph InterMap 6887 basemap program is the responsibility of the Ministry of 
ImageStation for aerotriangulation, DTM generation and Interior. The next five-year plan of updating the 
orthophoto rectification; 3) Filmrecorder for orthophoto basemaps will be switching to the digital format. Due to 
map production. rapid urban development in recent years, priority for 
updating will be given to the 1:5000 scale maps first. 
Although both projects are using the latest digital 
photogrammetric technique, their workflows are Basemap Productions. On this project, aerial photos 
somewhat different. This is primarily attributed to the taken at 1:18000 scale are having an end lap of 80 
different requirements of black-and-white versus color percent to allow for the possibility of selecting one photo 
and the superimposition of topographic linemap over covering one complete map quadrangle. Consequently, 
photo images. it allowed one photo making one map and no photo 
368 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996 
  
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