maintaining the shape of features, as well 
referring in the all job to a different reference 
system. 
In this case the relations are : 
Xt= [M+sin (R) +X] + [M+COS (R) + Y] +dX 
Yt= [M*C0S (R) *X] + [M+sin (R) + Y] +dY 
where 
- Xt and Yt are the coordinates oriented in the 
reference system of the map sheet 
- X and Y are the image coordinates (digitalized) 
- R rotation 
- M scale factor 
3.3 Projective Transformation and 
rototranslation 
This procedure requires a minimum of 4 points. It 
is used when we need to correct a bi-axial non- 
linear (polynomial) deformation of the image. 
This could happen using a commercial scanner to 
acquire the raster image of the map sheet. 
The transformation is based on the following 
relations: 
Xt= Al*X*A2*Y*A3 
B1*X*B2*Y*1 
_ Ad+X+A5+Y+A6 
Yt 
BixX+B2*Y+1 
where 
- Xt and Yt are the coordinates oriented in the 
reference system of the map sheet 
- X and Y are the image coordinates (digitalized) 
- Al,A2,A3,A4,A5,A6,B1,B2 unknown parameter for 
rototranslation 
By means of rototranslation all the coordinates 
collected by the digitalization are transformed 
in the map sheet reference system. 
At this point it is possible to manipulate the 
file coordinates for the final editing through 
the GALILEO SISCAM software packages  (GPM, 
OVERMAP/C) or to convert them in any other format 
(DXF). 
DIGIRAST will be available for demonstration on 
site at the '92-ISPRS exhibition in the GALILEO 
SISCAM booth (# 812). 
Additional information as well as data about 
performances, precision and comparison with 
traditional hand digitalization will be provided 
inquiring directly to GALILEO SISCAM, Via 
A.Einstein 35a, Campi Bisenzio 50013, Firenze, 
Italy (tel +39+55+8969191 - fax +39+5+8969064) 
492 
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