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INTRODUCTION 
New computer technology, improved software systems and overall computer awareness of 
individuals has greatly impacted the way in which we carry out daily lives. GIS technology has 
been the benefactor of these changes since one of the major constraints of early systems was the 
large amount of computer power required to make them work. Hardware and software advances 
have brought GIS to the desktop and the corresponding benefits to the organization are beginning 
to be realized. 
Another major constraint to developing successful systems is providing current, accurate, reliable 
spatial data to serve as the foundation for GIS applications. Some vector data sets are available 
over a wide area, however, they usually require a substantiai amount of effort to bring them into 
a GIS usable form. In the case of digital topographic map data the problem is further 
exacerbated by the fact that data which are available are often at small scales and are not up to 
date and therefore may not meet the spatial accuracy or content requirements of the user. 
One new technology which has proven itself over the past few years is Digital Orthophoto 
Imagery (DOI). Data products made using DOI technology can provide a cost effective solution 
to the mapping problem while at the same time delivering a data set which provides substantial 
extra value to the GIS user. 
This paper will explore the concepts behind DOI, examine the pros and cons for DOI as a GIS 
data set and relate the experiences to date of Linnet Graphics International (LGI) in producing 
DOI data for the Manitoba Land Related Information System (MLRIS). 
WHAT IS DOI 
DOI technology evolved out of the remote sensing community in response to the requirement 
to spatially correct digital data obtained from satellite sensors. In order to use these data for 
analysis it is necessary to remove the distortions caused by sensor operation and to provide an 
orthogonal picture which can be oriented to fit the earth based geodetic reference system. With 
these corrections performed it is possible to accurately locate the digital data relative to it's 
corresponding place on the earth surface and thereby enhance the useability of the data for 
analysis purposes. The restitution of data obtained from space based platforms requires not only 
the modelling of complex geometry, digital elevation terrain data and sensor performance 
Characteristics, but also requires the manipulation of large raster data sets. These same 
principles, when applied to imagery obtained from aerial camera system, have resulted in the 
development of DOI technology. Early systems developed for this purpose required extensive 
computing power, however, the latest systems are taking advantage of PC processing power and 
are providing the rectification functionality on the desk top. Full production systems still require 
strong computer systems but the functionality of DOI is being found in most GIS vendor 
Software today. 
In the traditional mapping community the procedures and technology for producing hard copy 
orthophoto maps has been well known and used for almost thirty years. Although these products 
provided users with an enhanced presentation of traditional topographic features, the fact that 
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