AN ADVANCED SENSOR MODEL FOR PANORAMIC CAMERAS
Jafar Amiri Parian, Armin Gruen
Institute of Geodesy and Photogrammetry
Swiss Federal Institute of Technology (ETH) Zurich
(parian, agruen)(geod.baug.ethz.ch
Commission V, WG V/1
KEY WORDS: Close Range, Photogrammetry, Panoramic Camera, Calibration, Sensor, Modeling, Accuracy, Test
ABSTRACT:
Digital terrestrial panoramic cameras constitute an interesting new development, which is currently primarily used for purely imaging
purposes such as indoor imaging, landscape recording, tourism advertising and Internet representations. However, the capability of
taking high-resolution images continuously over the full horizon generates an efficient means for 3D object reconstruction as well.
For that the particular sensor model has to be established and the inherent accuracy potential has to be investigated. We designed a
sensor model, which models substantial deviations from the pinhole model using additional parameters. The sensor model maps the
object space into the image space. The mapping function is the pinhole model-based perspective transformation in the form of bundle
equations. In practice, there are many systematic errors disturbing the ideal model, which can be modeled as additional parameters.
Additional parameters relate to the camera itself, the configuration of camera and turntable, and mechanical errors of the camera
system during rotation (i.e. tumbling). In this paper we will present the results of calibration with additional parameters for two
panoramic cameras, which indicate a subpixel accuracy level for such highly dynamic systems. We also investigate into the problem
of temporal stability of the systematic errors. Finally we will demonstrate the systems’ accuracy in 3D point positioning, including
minimal number of control points adjustment. With these new panoramic imaging devices we do have additional powerful sensors
for image recording and efficient 3D object modeling.
1. INTRODUCTION
The first panoramic cameras used in Photogrammetry were
film-based aerial cameras. The Manual of Photogrammetry,
1980 lists a number of types, which differ mechanically and
optically from each other. A prototype of an aerial panoramic
camera can be modeled as a camera with a cylindrical focal
surface, in which the image is acquired by sweeping a slit across
this surface (Hartley, 1993). Through the integration of CCD
technology, new types of airborne and terrestrial digital
panoramic cameras were generated, using Linear Array CCDs
as imaging devices. The EYESCAN, jointly developed by
German Aerospace Center (DLR) and KST Dresden GmbH and
the SpheroCam, SpheronVR AG are two different types of
line-based panoramic cameras. The EYESCAN camera as used
in terrestrial photogrammetric applications was addressed in
Scheibe et al, 2001. Schneider and Maas, 2003 and Amiri
Parian and Gruen, 2003 have worked on the mathematical
modeling of line-based panoramic cameras. Schneider and Maas
investigated a geometrical model for a prototype of the
EYESCAN panoramic camera and they performed calibration
by using a 3D testfield (Schneider and Maas, 2003). They also
performed 3D positioning using bundle block adjustment
(Schneider and Maas, 2004). We have worked on the
mathematical model of general line-based panoramic cameras.
We performed calibration and accuracy test using a 3D testfield
for EYESCAN and SpheroCam (Amiri Parian and Gruen,
2003). We improved mathematical model by modeling the
mechanical error of the rotating turntable, tumbeling, and we
reported the improvement of the accuracy by a factor of two in
the case of using tumbling parameters in the bundle adjustment
process (Amiri Parian and Gruen, 2004).
In this paper, by defining image- and block-invariant parameters
we put emphasis on 3D positioning using a minimal number of
control points. The paper will be organized as follows. Chapter
| gives a short review of the panoramic cameras SpheroCam
and EYESCAN. Chapter 2 addresses our mathematical sensor
model. Chapter 4 covers the result of adjustment, included the
results of the physical measurement of the tumbling for the
SpheroCam, and the calibration results of EYESCAN
with/without tumbling parameters. In this chapter we
demonstrate the system accuracy for EYESCAN using a
testfield with as few as possible control points.
2. PANORAMA TECHNIQUES
Several techniques have been used for panoramic imaging.
Mosaicing/stitching of a rotated frame-CCD camera, mirror
technology including single mirror and multi mirrors, near 180
degrees with large frame cameras or one shot with fish-eye lens
and recently a new technology of creating high resolution
panoramic image by rotating a line-CCD camera are some
known methods for panoramic imaging. Up to now, these
techniques have mainly been used for pure imaging purposes,
such as indoor imaging, landscape and cultural heritage
recording, tourism advertising and image-based rendering, and
recently for efficient Internet representations. Among the
mentioned techniques for panoramic imaging, the last one has a
possibility to produce a high-resolution panoramic image (more
than 300 Mpixels) in onc shot. The camera principle consists of
a lincar array, which is mounted on a high precision turntable
parallel to the rotation axis. By rotation of the turntable, the
linear array sensor captures the scenery as a continuous set of
vertical scan lines.
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