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Automatic Measurement of Plate Coordinates in order to Obtain 
Automatic Plotting . 
Bai Agnoletto Elena? Casalini PierLuigi"", Lombardi Stefano", 
Tonazzini Anna”** 
au Geod.Top.Fotog., Fac.ing., Univ. of Pisa, Italv 
e **Ist. Scienze dell’ Informazione, Univ. of Pisa, Italy.. 
“Ist.Elaborazione dell’ Informazione, CNR, Pisa, Italy 
Working Group II/2 
  
  
1. introduction 
This paper discusses the problem of obtaining a completely auto- 
matic restitution of particuiar takes in terrestrial photogram- 
metry (3). 
The aim is to determine automatically the plate coordinates of 
corresponding points on a pair of stereoscopic photograms. 
At present, the most common tendency is to define and design 
image correlators (1),(2), i.e. sophisticated instruments gen- 
erally designed ad hoc, which substitute the stereoscopic vision 
by adequate photoelectric and electronic systems. Essentially, 
these systems provide a rapid and accurate sensing of parallax 
by scanning and subsequently correlating corresponding imageries. 
The approach taken here is completely digital, using the typical 
image processing system, and analysing separately the two photo- 
grams. The system adopted consists essentially of: 1) an analog- 
to-digital converter (digitizer), which converts each photogram 
of the stereoscopic pair into digital information, 2) a digital 
computer, 3) a TV monitor for data display, and 4) «a plotter for 
mapping. 
2. Photogram taking techniques 
The problem was approached in stages andour study was limited to 
terrestrial takes obtained with special artifice, i.e. by pro- 
jecting a bright plane raster onto the surface to be taken. The 
raster is made up of two series of parallel straight lines in- 
tersecting each other at 90° at points called nodes. The nodes 
projected on the object enable us to identify in the stereosco- 
pic pair corresponding points in cases where the homogeneity of 
colour and the lack of light and shades of the Pasa make 
this operation difficult and at times impossible 
similarly, the characterization of the points to be restituted 
by mathematically definable forms (the nodes of the raster) 
facilitates automatic measurements by the computer. 
Moreover, the raster can be considered a photogram (pseudophoto- 
ram) obtained by a particular take of theobiect. . In fact, we 
can make the following considerations: