PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
May 2019
345
Special Issue on the
ISPRS TCII Symposium 2018
Fabio Remondino and Isabella Toschi, Guest Editors
This
PE&RS
Special Issue originates from the ISPRS
Technical Commission II Midterm Symposium (
.
org/tc2-symposium2018), that was held in Riva del Garda,
Italy, in June 2018. ISPRS TCII “Photogrammetry” covers
all aspects of measurement and information extraction in
photogrammetry, with special focus on the geometric, radio-
metric and multi-temporal aspects of 3D imaging techniques.
Particularly, the uniqueness of TCII mainly comes from its
multi-scale perspective, encompassing theory and methods
to derive accurate information from terrestrial, aerial and
satellite images and point clouds, in various application
fields – industrial metrology, heritage, geosciences, etc. These
elements made the TCII Midterm Symposium a reference
meeting point for researchers, practitioners and companies
working in the field of photogrammetry, computer vision,
geospatial data analysis and point cloud processing.
As event organizers, we selected the most promising contri-
butions, that convey deep insight into the latest advances
of photogrammetry, from image orientation and point cloud
generation, to 3D scene reconstruction and large-scale
machine learning methods for geospatial analysis. Data
acquisition and processing in underwater and environmental
applications are also treated. This Special Issue contains the
most salient outcomes of the studies presented at the Sympo-
sium, and includes 10 peer-reviewed papers grouped into two
issues.
In this issue, the reader will find the following articles
Robust Structure from Motion Based on Relative Rotations and Tie
Points
This paper will present two novel approaches for image
orientation with a focus on robustness, starting with relative
orientations of available image pairs, an incremental and a
global one, and compare their performance. For the incre-
mental approach, we first choose a suitable initial image
pair, and we then iteratively extend a cluster by adding new
images. The rotation of these newly added images is estimat-
ed from relative rotations by single rotation averaging. In
the next step, a linear equation system is set up for each new
image to solve the translation parameters with triangulated
tie points which can be viewed in that new image, followed by
a resection for refinement. Finally, we refine the orientation
parameters of the images by a local bundle adjustment. We
also present a global method, which consists of two parts:
global rotation averaging, followed by setting up a large
linear equation system to solve for all image translation
parameters simultaneously, a final bundle adjustment is car-
ried out to refine the results. We compare these two methods
by analyzing results on different benchmark sets including
ordered and unordered image datasets from the Internet and
two other challenging datasets to demonstrate the perfor-
mance of our two approaches. We conclude that while the in-
cremental method typically yields results of higher accuracy
and performs better on the challenging datasets, our global
method runs significantly faster.
Flexible Photogrammetric Computations using Modular Bundle
Adjustment
The main purpose of this paper is to show that photogram-
metric bundle adjustment computations can be sequentially
organized into modules. Furthermore, the chain rule can be
used to simplify the computation of the analytical Jacobians
needed by the adjustment. Novel projection models can be
flexibly evaluated by inserting, modifying, or swapping the
order of selected modules.
As a proof of concept, two variants of the pin-hole projec-
tion model with Brown lens distortion were implemented in
the open-source Damped Bundle Adjustment Toolbox (DBAT)
and applied to simulated and calibration data for a non-con-
ventional lens system. The results show a significant differ-
ence for the simulated, error-free, data but not for the real
calibration data.
The current flexible implementation incurs a performance
loss. However, in cases where flexibility is more important,
the modular formulation should be a useful tool to investigate
novel sensors, data processing techniques, and refractive
models.
Aiding Indoor Photogrammetry with UWB Sensors
Given the worldwide spread of smartphones, photogrammet-
ric surveying with mobile devices is becoming of significant
interest in the research community for providing low cost
3D models. Since the photogrammetric procedure applied
to images produces a projective model, some external infor-
mation is needed in order to obtain a 3D metric model. To
this aim, GNSS measurements are typically aided to the
photogrammetric reconstruction procedure. However, the
quality of the obtained reconstruction is related to the GNSS
positioning accuracy, which is typically at meter-level for
cheap receivers as those embedded in most of the consumer
mobile devices, e.g. smartphones. Furthermore, this approach
