Full text: Proceedings, XXth congress (Part 8)

Dimitar Jechev 
GIS Sofia Ltd., Bulgaria, BG-1000 Sofia, 5 Serdika Str., e-mail: jechev@gis-sofia.bg 
Commission V, WG V/4 
KEY WORDS: Close-range, Non-metric, Experiment, Digital, Adjustment, Building 
A frontage of a building has been experim 
geodetic. The photogrammetric survey has been made by means of 
station. The shortcomings of the amateur hardware, that have been used for the experiment, were c 
entally surveyed and processed in two basically different methods — photogrammetric and 
an amateur digital camera, and the geodetic survey - by a total 
ompensated by application of a 
specific mathematical model. The results from the two surveys performed have been compared. The RMS in the plane of the picture 
(the building frontage) has been calculated to be +1 .9 cm and for the 
Racurs Co. has been used for this experiment. 
1.1. Problems 
The work with non-metric cameras for photogrammetric 
purposes is accompanied by the following problems: 
e Defining the image co-ordinate system (non-metric 
cameras do not have fiducial marks). 
e Defining the unknown elements of internal orientation 
(focal length and image co-ordinates of the principle poin 
of the photograph). 
e Maintaining the elements of internal orientation unchanged 
in time - usually when working with non-metric cameras, 
the elements of internal orientation get slightly changed 
after every single exposure. 
e Defining the distortion of lens - the distortion with 
amateur cameras often amounts to considerable values and 
have substantial effect. 
1.2. Solving the problems 
There are three basically different methods for solving the 
above mentioned problems known: 
Calibration in advance. Before surveying, in a laboratory 
(calibration centre) the unknown elements of internal 
orientation and distortion of lens shall be defined. The 
advantage of this method is that the calibration takes place 
at a laboratory and hence better accuracy at defining of 
unknown quantities is achieved. The problem with their 
fluctuation in time remains. 
Calibration during the processing. The unknown 
elements are defined by means of a special mathematical 
instrument. A larger number of control points is needed for 
their defining - at least 5 points, and it is recommendable 
8-10 points per model, compared to 3 points per model 
when using metric camera. 
Self-calibration. It is based on the mathematical means of 
the geometry of overlapped areas for defining the unknown 
elements. The principles involved are similar to the ones, 
used for relative orientation of stereo-pair with analogue 
instrument. It is specific for this method that it does not 
require larger number of control points. 
depth £6.1 cm. Photogrammetric software PHOTOMOD Lite of 
1.3. Mathematical processing 
In accordance with the co-linearity condition, every object 
point, its image and the projection centre, should belong to one 
and same line, called ray. Mathematically this can be 
represented by means of the following 3 equations: 
X; X X X, | 
Y jm yg 4; R Y Y ( | ) 
0 f z Z, | 
where: i=1 2 ..n 
is the number of measured image points, 
(s, y. 0) are image co-ordinates of point 1, 
NT (t . . 
Kos Vort ) are the elements of internal orientation, 
À, is the scale factor, 
R is the rotation matrix, defining the 
spatial rotation of the geodetic co- 
ordinate system in relation to the image 
co-ordinate system. R is function of the 
three angles @ , ¢, K, 
(X, , y ? Z, y 
(34.3.2, y are 
projection centre O. 
are the geodetic co-ordinates of point i, 
the geodetic co-ordinates of 
It is not justifiable to render different scale factor for each i 
point. The scale factor could be eliminated by dividing the first 
and second equations from the system by the third one: 
HH (x —A m,,(Y, = Y), + m,(Z, - Z,) 
P =x —x,+ i T ali 
eS nl m,, (x, — X.) mar, -Y,)yrmad zz) 
T y m4 (X, — X,}+m, (Y, = Y) +my(Z, -Z,) E 
REY TNT. m, (X, — X m,, (Y, — Y,)- m, -4 s 
where: m are the elements of R matrix

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