# Full text: Proceedings, XXth congress (Part 8)

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CLOSE-RANGE PHOTOGRAMMETRY WITH AMATEUR CAMERA
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
ABSTRACT:
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. THEORY
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.
136
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,
n
(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)
tt
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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