Application of terrestrial photogrammetry to the creation of a 3d model of the Saint Hedwig chapel in the Kanovice.
Mikolas, Milan ; Jadviscok, Petr ; Molcak, Vlastimil 等
Reference to this paper should be made as follows: Mikolas, M.;
Jadviscok, P.; Molcak, V. 2014. Application of terrestrial
photogrammetry to the creation of a 3D model of the Saint Hedwig Chapel
in the Kanovice, Geodesy and Cartography 40(1): 8-13.
Introduction
Terrestrial photogrammetry ranks among the methods that can be used
to survey building structures and assess three-dimensional models. This
method finds its use in the field of documentation of buildings,
particularly historical sites characterized by their rugged ground plan
and extensive number of decorative architectural elements. Such a survey
is usually performed with the use of the intersection method or the
single image method in cases where only a photomap (two-dimensional,
e.g. for purposes of facade measurement) is required in terms of
documentation. The objective of photogrammetric surveys is to determine
the dimensions and the shape of the structure of interest including the
visualization of three-dimensional or two-dimensional output.
Photogrammetric documentation has significance mainly for documentation
purposes, it allows for evaluation of the current state of the surveyed
structure or for comparison of the results of periodic photogrammetric
survey; that can be particularly convenient for monitoring of structures
subject to horizontal as well as vertical deformations due to the
negative impact of the underground mining activity.
1. Software and instrumental equipment
The purpose of the photogrammetric documentation is always a
decisive factor for the selection of instrumental equipment and
realization of the photogrammetric survey of any structure. Among other
criteria of the appropriate instrumental or software equipment selection
are issues related to the expected accuracy of any survey and of the 3D
model and as well as the requirements regarding the visualization or
presentation of the 3D or 2D photogrammetric output. For the purposes of
a simple photogrammetric documentation; it is adequate to realize the
photogrammetric survey using any widely accessible non-survey digital
camera. In the case of increased requirements on the accuracy or quality
of the processed photographs, it is necessary to use a professional
digital single-lens reflex camera producing photographs with high
resolution. The photographs that served as a basis for the creation of
the 3D model of the structure were taken with the Samsung S760 digital
camera (see Fig. 1) with resolution 7.2 million effective pixels. An
indispensable part of the instrumental equipment and software is
comprised of tools necessary for the calibration of the camera and for
the connection of the 3D model to the scale. Among these tools are in
particular the following: a geodetic control serving the automatic
digital camera calibration by means of the PhotoModeler 6 software and a
survey tape for the control side measurement serving to connect the
model to the scale as well as to test the accuracy of the
photogrammetric survey.
2. Digital camera calibration and photographing of the structure of
interest
One of the preconditions for successful creation of a 3D model of
the structure is compliance with certain rules that apply to the
photographing of the structure of interest which will be mentioned
hereafter, and the use of a properly calibrated digital camera.. The
term "calibration" refers to a set of operations leading to
the determination of important parameters of the camera which are
indispensable for the evaluation of the surveyed photographs. The
calibration process results in elements of internal orientation, such as
the camera constant, the position of the principal point of the
photograph, the distortion of the lens system, and the dimensions of the
digital chip (Kapica, Sladkova 2011).
For purposes of the digital camera calibration, it is possible to
use either a 2D geodetic control or a 3D geodetic control. This article
focuses on the process of calibration by means of a 2D geodetic control
of the PhotoModeler 6 software depicted in Fig. 2. The 2D geodetic
control is constituted by a grid of points represented by black circles
with four control points in the corners of the control
(Suziedelyte-Visockiene 2012). To evaluate the calibration, it is
necessary to take 8 photographs before the photographing of geodetic
control itself; furthermore, it is imperative to comply with the
following rules: a) the geodetic control must be placed on a horizontal
mat, b) the geodetic control should be without any shadows, c) all
photographs must be taken with a constant focal length (do not use the
ZOOM function), d) the maximum resolution must be set, e) the
photographs must be constant, f) the calibration field must fill the
maximum possible space of the photograph, as the automatic calibration
might cause the program to include erroneously dark points on the
background of the geodetic control to the calculations, g) the camera
should not be switched off (inner orientation elements might change).
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
The next step is to take a total amount of 8 photographs of the
geodetic control under the angle of approximately 45[degrees] while
complying with the following rule: the photographs must be taken in
couples, one landscape, then the camera should be turned by 90[degrees]
and a portrait should be photographed from four stations (see Fig. 3).
The PhotoModeler 6 software allows for automatic calculation of all
required parameters. Following the import of photographs, the
calibration process will be initiated, resulting in a calibration
message that includes the required parameters of the camera; it is
possible to set these parameters for the project in the framework of
which the structure photographs will be processed. When this is
completed, it is possible to proceed to the next stage of work (Kapica
2009).
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
The following stage is related to operations resulting in
photographs of the modelled structure. In this case, the structure of
interest is the Saint Hedwig Chapel in Kanovice dating back to 1868. The
municipality of Kanoviceis located approximately 8 km to the North from
the town of Frydek-Mistek (see Fig. 4). The structure is owned by the
Catholic Parish of Bruzovice and is used for regular church services
(Oficialni stranky obce Kanovice 2011).
Prior to the photographing itself, it is necessary to perform
operations related to the terrain reconnaissance and operations
resulting in the appropriate choice of position of photogrammetric
stations depending on surrounding terrain, vegetation, and the spatial
character of the structure. In the process of photographing of the
structure, it is necessary to comply with the rules of intersection
photogrammetry, in particular to make sure that the angle of the
intersection of individual photographs' axes approaches the ideal
value, which is the intersection angle of 90[degrees]. To ensure the
continuity of individual photographs, it is necessary to provide a
sufficient overlapping so that each point of the structure is
represented at least on three photographs. Though it is not always
possible to respect all rules of photographing due to local conditions
in the vicinity of the modelled structure the surveyor should always try
to comply with the required rules as closely as possible. Fig. 5 depicts
a demonstration of photographs taken of the structure. We took a total
of 21 photographs.
[FIGURE 5 OMITTED]
For control purposes, for the purposes of connecting the 3D model
to the scale as well as defining the accuracy of the created model, it
is necessary to survey the control side measurements with a survey tape,
in case of higher accuracy requirements, it is convenient to choose
ground control points and survey and evaluate these by the standard
geodetic method. In this particular case, the survey of the control side
measurements with a survey tape was sufficient (Kapica, Sladkova 2011).
3. Creation of 3D model of the structure
The processing of photographs and the creation of the requested 3D
model of the structure was preceded by the selection of photographs to
be used for processing in the PhotoModeler software. It is always
convenient to take more photographs in the terrain and make the
selection afterwards, if necessary. We selected 13 photographs out of
the total number of 21 for subsequent processing.
The following operation is related to the referencing of the points
on individual photographs. The photographs of the structure must be
oriented; orientation of two photographs requires at least 6 common
points to be referenced on the photograph. The orientation of three
photographs requires the same condition of 6 identical common points to
be referenced while the three oriented photographs must necessarily have
at least one common point. It is therefore convenient, for purposes of
the photographs' orientation with respect to the abovementioned
conditions, to take identical points on conveniently selected pairs or
trios of photographs. The referencing is performed as follows: the
photograph of departure is defined, a point on the photograph of
departure is taken, and then identical points on other photographs are
taken. As soon as the number of taken points is sufficient, points of
the 3D model are calculated. A similar method is used to reference all
points constituting the basis of the 3D model. In the course of the
referencing process, a "wire-frame model" is created
(connecting of already calculated points of the 3D model by lines
directly on the photograph or in a 3D representation). The connection of
the model to the scale is performed by defining the real lengths
measured in the terrain corresponding to the line element in the 3D
model. To connect the model to the scale, we used the longest sides of
the structure. We subsequently defined the coordinate axes (Kapica
2009).
The final process in the creation of the 3D model of a structure is
the connection of surfaces to the wireframe model. It is possible to
connect real textures directly from the photograph to the wireframe
model or to use predefined materials that approximate the real
appearance of the structure. In this case, we used our own colour
definition of surfaces for individual elements of the structure
(windows, facade, roof, entry doors, etc.) according to the colour
scheme on the photographs. We used our own materials of surfaces for
reasons of local deformations of real textures on photographs. The use
of real textures for surfaces of the 3D model is not always possible as
it is conditioned by high resolution photographs (Mikulenka, Kapica,
Sladkova 2011). Demonstration of graphicaloutput to see Figs 6-11.
[FIGURE 6 OMITTED]
[FIGURE 7 OMITTED]
[FIGURE 8 OMITTED]
[FIGURE 9 OMITTED]
[FIGURE 10 OMITTED]
[FIGURE 11 OMITTED]
4. Accuracy evaluation of the 3D model of the chapel
To evaluate the accuracy of the created 3D model of the Saint
Hedwig Chapel it is possible to use the side measurements that were
measured in the terrain (type H: horizontal, V: vertical, see Table 1)
while the structure was photographed. The real lengths (measured by the
survey tape) are compared to lengths calculated by the PhotoModeler
software from the 3D model. The deviations and accuracy characteristics
are summarized in the table below. The accuracy characteristics of the
3D model of a structure are defined as empirical (experimental) mean
error of the model m (see Table 1). The calculation of the mean error
did not include the length by means of which the model was connected to
the scale.
Conclusions
The objective of the present article was to outline concisely the
issue of photogrammetric survey and to present the possibilities of the
graphical output in which the PhotoModeler software allows to produce
the survey results. The article explains individual operations related
to the photogrammetric survey as well as the processing of the 3D model
from the theoretical (rules of calibration, structure photographing,
creation of the 3D model) and practical perspective (in the form of
graphical demonstrations of the digital camera calibration,
photographing of the structure, creation of the 3D model of the
structure, and the presentation of results of a particular
photogrammetric survey). Furthermore, the article focuses on evaluation
of the accuracy of the 3D model from which we can note that for the
purposes of general documentation, evaluation of the current state of a
structure or 3D presentation of the structure of interest, the
photogrammetric survey and evaluation is sufficient with a widely
accessible camera and a survey tape. In the case of increased
requirements on accuracy in mm, it would be necessary to use a survey
camera (camera with stable inner orientation elements) in combination
with the survey of ground control points by the standard terrestrial
geodetic method. Beside the abovementioned forms of graphical output,
the PhotoModeler software offers other possibilities of presentation of
results in the form of 3D animations or connection and inclusion of a
created 3D model to the environment of Google Earth applications,
including the option of exporting the results to various other formats.
This article was written in connection with grant project SGS No.
SP2014/13--The use of UAV device for creating 3D models in geodetic
practice.
Caption: Fig. 1. Digital camera Samsung S760
Caption: Fig. 2. Photographs of the 2D geodetic control
Caption: Fig. 3. 3D model of the calibration field including the
station position
Caption: Fig. 4. Structure localization (GPS
49[degrees]44'31" N, 18[degrees]23'20" E)
Caption: Fig. 5. Demonstration of photographs of the Saint Hedwig
Chapel
Caption: Fig. 6. 3D model with the position of photogrammetric
stations (view 1)
Caption: Fig. 7. 3D model with the position of photogrammetric
stations (view 2)
Caption: Fig. 8. Wireframe model connected with the photograph
Caption: Fig. 9. 3D model (ground plan + photograph stations)
Caption: Fig. 10. 3D model of the chapel connected to photographs
taken
Caption: Fig. 11. 3D model of the Saint Hedwig Chapel (3D
visualisation)
doi: 10.3846/20296991.2014.906923
References
Kapica, R. 2009. Fotogrammetrie Ndvody do cviceni I., II. Ceska
republika, Vysoka skola banska, Technicka univerzita Ostrava, 57 s.
ISBN: 978-80-248-2067-5
Kapica, R.; Sladkova, D. 2011. Photogrammetric analysis of objects
in undermined territories, Geodesy and Cartography 37(02): 49-55. ISSN
2029-6991 print, ISSN 20297009 online.
http://dx.doi.org/10.3846/13921541.2011.586440
Mikulenka, V.; Kapica, R.; Sladkova, D. 2011. The potential of
photogrammetry for object monitoring in undermined areas, Acta
Montanistica Slovaca 16: 262-269. ISSN 13351788.
Oficidlnistrdnky obce Kanovice. 2011. Informace o obci Kanovice
[online], [cited 11 May 2011]. Available from Internet:
http://www.obec-kanovice.cz/?page=obec&set=cz-34686
Suziedelyte-Visockiene, J. 2012. Photogrammetry requirements for
digital camera calibration applying TCC and MatLab software, Geodesy and
Cartography 38(3): 106-110.
http://dx.doi.org/10.3846/20296991.2012.728895
Milan MIKOLAS. Doc. Ing., Ph. D. VSB--TU Ostrava, Institute of
Mining Engineering and Safety, Faculty of Mining and Geology,
VSB--Technical University of Ostrava. 17. Listopadu 15, CZ 708
33Ostrava, Czech Republic. Ph+ 420608533231, e-mail:
milan.mikolas@vsb.cz Research interest: mining engineering and safety.
Petr JADVISCOK. Ing. VSB--TU Ostrava, Institute of Geodesy and Mine
Surveying, Faculty of Mining and Geology, VSB--Technical University of
Ostrava, 17. Listopadu 15, CZ 708 33 Ostrava, Czech Republic.
Ph+420724087561, e-mail: petr.jadviscok.st1@vsb.cz
Research interest: the issues of precision GNSS technology in
surveying practice.
Vlastimil MOLCAK. Ing. VSB--TU Ostrava, Institute of Geodesy and
Mine Surveying, Faculty of Mining and Geology, VSB--Technical University
of Ostrava, 17.listopadu 15,CZ 708 33 Ostrava, Czech Republic. Ph
+420728365563, e-mail: vlastimil.molcak.st@vsb.cz
Research interest: verification of the coefficients of theoretical
calculations of movements and deformations in the mining area Staric.
Milan Mikolas (1), Petr Jadviscok (2), Vlastimil Molcak (3)
(1) Institute of Mining Engineering and Safety, Faculty of Mining
and Geology, VSB--Technical University of Ostrava, 17.listopadu 15, CZ
708 33 Ostrava, Czech Republic
(2,3) Institute of Geodesy and Mine Surveying, Faculty of Mining
and Geology, VSB--Technical University of Ostrava, 17.listopadu 15, CZ
708 33 Ostrava, Czech Republic
E-mails: (1) milan.mikolas@vsb.cz (corresponding author); (2)
petr.jadviscok.st1@vsb.cz; (3) vlastimil.molcak.st@vsb.cz
Submitted 13 February 2014; accepted 24 February 2014
Table 1. Accuracy evaluation of the 3D model
n type Terrain PhotoModeler v vv
[m] [m] [cm] [[cm.sup.2]]
1 H 5.26 5.27 -1 1
2 H 2.23 2.24 -1 1
3 H 2.23 2.20 3 9
4 H 2.21 2.20 1 1
5 H 3.68 3.66 2 4
6 H 4.85 4.83 2 4
7 H 3.72 3.69 3 9
8 H 6.36 6.36 0 0
9 V 2.15 2.14 1 1
10 V 2.95 2.99 -4 16
11 V 1.45 1.44 1 1
12 V 2.65 2.63 2 4
13 V 0.80 0.79 1 1
14 V 2.18 2.20 -2 4
15 V 2.97 3.00 -3 9
[SUMMATION] 65
Mean error of the 3D model m = 2.1 cm
