SIMULTANEOUS GEOREFERENCING OF DIGITISED HETEROGEIOUS MAP 
SHEETS 
R. Mahmoudi, B. Takarlı, M. Benmohamed 
Geomatic Laboratory, Centre National des Techniques Spatiales, BP 13, Arzew, 31200 Algeria 
Commission VI, WG VI/4 
KEY WORDS: Individual map sheet, simultaneous georeferencing, tie points, independent model, linear transformation 
ABSTRACT: 
One of the most important phases in the set up of a GIS is the recovery of existing data and then maintain it in a consistent format. 
This data may originate from different sources, various media, and be acquired by various techniques at different scales. To be useful 
the data must be placed into homogeneous system and referenced to the same co-ordinate system. For this purpose, the application of 
efficient adjustment techniques is mandatory. The paper describes application of a photogrammetric block adjustment technique 
(independent model triangulation) for simultaneous georeferencing of digitised map sheets. This technique allows us to establish 
compatibility between sheets as well as data homogeneity and continuity for eventual updating. The technique can efficiently resolve 
problems that may arise between individual sheets because of: different co-ordinate systems, different scales, different media (paper, 
film), lack of controls points, and inappropriate distribution of control points. This approach was applied to set up a land information 
system to identify and indemnify landowners before initiation of an industrial compound construction. 
1. INTRODUCTION because of different characteristics of each individual sheet 
(scale, medium, precision, control points, maintenance). 
The incorporation of cadastral data into a GIS requires that all 
data must be referenced precisely to the same co-ordinate 
system. When the source data originate from existing map Figure 1. Local and state co-ordinate system - individual sheet 
sheets or orthophotos we may be confronted with many 
problems such as: 
1. Different co-ordinate system in different sheets 
Different scales 
Different media (paper, film) 
Lack of control points 
Inappropriate distribution of control points. 
  
COSS 
State system 
The problems appear especially often in countries in transition, 
The simultaneous adjustment of the adjacent sheets into the Local system 
same and unique co-ordinate system is then a suitable solution. 
It allows precise establishment of the relations between sheets 
  
  
  
and guarantees the continuity of data acquisition. The technique Each sheet must have a sufficient number of control points for 
is based on the well-known photogrammetric independent the determination of transformation parameters. It may happen 
model adjustment. We only substitute a photogrammetric model that a point appearing in several sheets shows co-ordinate 
by a sheet. The adjustment is based on successive discrepancies in each sheet. By using a non-linear 
transformations of adjacent sheets into common co-ordinate transformation this approach can be applied to derive 
system and then transformation of that common system into an approximate solution for the global adjustment. 
official co-ordinate system. The technique has been verified in 
photogrammetric practice and can be easily incorporated into a 2.2 Simultaneous sheet adjustment 
GIS . 
This procedure is based on simultaneous treatment of all 
2. GEOREFERENCING TECHNIQUES neighbouring sheets taking into account common points on 
sheet overlaps (tie points, junction points). On one hand it takes 
2.1 Individual sheets care to adjust neighbouring sheets relatively with each other by 
minimising tie point discrepancies and on the other hand it 
Georeferencing of individual sheets is based on individual adjusts the whole structure absolutely into the state co-ordinate 
transformation of a local sheet co-ordinate system into an ^ system by minimising the discrepancies on control points. This 
accepted state plane co-ordinate system approach requires overlap between adjacent sheets 
This approach does not guarantee correct edge matching. The The advantages of the approach are: 
edge matching between adjacent sheets may become poor I. Control points are not required in every sheet. 
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