ENHANCING THE PROSPECTS FOR MAPPING FROM HIGH-RESOLUTION 
SATELLITE IMAGERY IN THE DEVELOPING WORLD 
Itthi Trisirisatayawong®, Thanate Jongrugenun“, Banjerd Phalakarn“, Chalermchon Satirapod", Clive Fraser” 
* Geo-Image Technology Research Unit, Dept. of Survey Engineering, Chulalongkorn University, Bangkok, Thailand — 
itthi@chula.ac.th, thanate.j@chula.com, fsvbpl@eng.chula.ac.th, chalermchon.s@chula.ac.th 
? Dept. of Geomatics, University of Melbourne, Victoria 3010, Australia - c.fraser@unimelb.edu.au 
KEY WORDS: Imagery, High resolution, Mapping, Accuracy, Orthorectification, Sensor, Orientation 
ABSTRACT: 
High-resolution satellite imagery (HRSI) has demonstrated the capability of generating orthoimagery and DTMs that meet 
topographic map specification to 1:10,000 scale. Moreover, the generation of image-derived products from HRSI requires very little 
in the way of ground survey data, thus making this imagery an ideal mapping tool for the developing world. However, the cost of 
HRSI remains a significant factor limiting its application for large-scale mapping where metric tolerance are most stringent. Taking 
IKONOS imagery as an example, base-level, 15m accurate (CE90) Geo imagery sells for about $US 20/km?, whereas the 4m 
accurate Precision image product can cost upwards of $US 120/km? in Africa and Asia. A very attractive proposition for mapmakers 
in the developing world, therefore, would be to have the capability of generating the metre-level accuracy of Precision imagery at 
the price of base-level Geo imagery. 
This paper addresses the means to realize this prospect through discussion of the results of experimental testing of stereo IKONOS 
Geo imagery in Northern Thailand. Geopositioning accuracy to better than Im RMS in planimetry and around 1.3m in height was 
achieved with very few control points. The technique of bias-compensated rational functions was applied, along with a second 
sensor orientation model, using 6-8 ground control points. This produced geopositioning accuracy that met map specifications at 
1:10,000 scale. The paper highlights that lowest-cost HRSI products can meet the large-scale mapping needs of developing 
countries, thus leading to a more economical means of providing this important spatial data infrastructure component. 
1. INTRODUCTION large and medium scale maps are non-existent. Using satellite 
imagery is arguably the only practical way to remedy the 
High resolution satellite imagery such as 1-m resolution situation. But spatial resolution provided by previous generation 
IKONOS has generated much interest in the mapping and geo- spaceborne imaging systems such as Landsat or SPOT is too 
information community in Thailand. To date, any mapping low for many mapping purposes. For example, in the case of 
project using aerial photographs must seek permission from the coral reef mapping, a study by Trisirisatayawong and Samanloh 
military, the Royal Thai Survey Department (RTSD), who also (2003) that used Landsat 7 imagery to detect small shallow- 
control all the processes from taking the photographs through to water coral reefs which are the majority type in Thailand, 
archiving and distributing the data. Although lately control has showed that only limited success can be achieved and higher 
been relaxed, the time period required before users get the data spatial resolution imageries are required for more detailed reef 
is still quite considerable. The availability of HRSI in the mapping. HRSI exhibits significant spectral advantages over 
international market, coupled with the promise of fast data lower resolution satellite imaging systems such as Landsat and 
delivery, is much welcomed by users. However, for a large Spot, as well as strong geometric capabilities that previously 
mapping project the price of HRSI may not be as competitive at have not been available. These include much better 
present as aerial photograph, though this is still the subject of photogrammetric stereo capability and a higher revisit rate (Li, 
much debate. 1998). 
There are situations in which HRSI clearly has advantages over A large number of technical papers have demonstrated the . 
aerial photographs. An example in the Thai context is the metric capability of HRSI for large scale mapping. A user can 
mapping of small remote areas, especially those close to opt for off-the-shelf image products such as 4-m accurate 
national borders where mobilization of airplanes can be very (CE90) Precision Plus IKONOS imagery provided by Space 
expensive and flying airplanes is normally prohibited by the Imaging. The users, however, have to supply ground control 
Government in these regions. Another example is the mapping points to the company. Alternatively, users can purchase less 
of islands and off-shore natural resources such as coral reefs. accurate but also less expensive products such as Geo or 
There are more than 400 coral reefs in Thai waters and a Reference and get more accurate output by applying further 
substantial portion of the economy, particularly fishing and processing themselves. In a country of low-wages, but with à 
tourism, are underpinned by these resources. Again the problem solid technological base, like Thailand, the latter approach 
here is either the high cost of mobilizing the plane to take only seems to be more attractive. The gain from purchasing cheap 
a few photographs or the inaccessibility of the areas, which may product can easily offset the cost incurred from extra data 
lie too close to border areas. As a result, there are areas where processing. 
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