Conclusions and Outlook
In this paper, we presented a novel 360° stereo panorama
camera configuration for mobile mapping platforms. Two
360° panorama cameras, tilted forward and backward by 90°,
respectively, enable 360° stereo image acquisition with large
baselines. Conventional forward and backward looking stereo
systems contribute to a full 360° multi-view stereo coverage.
We evaluated the proposed approach by building an image-
based mobile mapping system based on the new approach.
The new mobile mapping system fulfills the accuracy re-
quirements and complies with strict privacy laws, such as in
Switzerland. We successfully implemented a rigorous sensor
and system calibration procedure, which also supports the
equidistant camera model for fisheye lenses. We calibrated
both the 11
MP
pinhole cameras of the forward facing stereo
system and the 5
MP
fisheye heads of the Ladybug5 panorama
cameras with the same accuracy. Moreover, we significantly
increased the calibration accuracy compared to Burkhard
et
al
. (2012). Furthemore, in order to generate geospatial 3D im-
ages and 3D image spaces (Nebiker
et al
., 2015) from fisheye
stereo images, we developed an image processing workflow
according to Abraham and Förstner (2005). Since a resulting
3D geospatial image consists of the left image of the corrected
equidistant stereo image pair with RGB channels and an addi-
tional disparity channel with perspective disparities, 3D point
coordinates can be easily determined with 3D mono-plotting.
We evaluated the accuracies in a challenging urban area in
the city center of Basel using 3D geospatial images captured
with our 360° panoramic stereo mobile mapping system. The
standard deviations of absolute 3D point coordinates were
in the range of 2 to 8 cm and those of relative 3D distances
were in the range of 1 to 5 cm for typical object distances in
the order of 10 m. Moreover, with our camera setup the image
radius appeared to have no significant error influence. Our
results with fisheye stereo systems do not differ significantly
from the results with pinhole stereo systems obtained by
Burkhard
et al
. (2012). With our captured and georeferenced
360° mobile mapping imagery, we automatically created a
3D city model with the 3D reconstruction software Context-
Capture from Bentley. The result is a very high detailed and
almost complete 3D city model of the street environment.
Overall, the novel 360° stereo panorama camera configura-
tion is equivalent in terms of accuracy to the former stereo
camera configuration with the advantage of a full 360° stereo
coverage. In the future, we can host equidistant 3D geospatial
images in cloud-based web services. Thus, we can realize cli-
ent applications with 360° image coverage and measurement
functionality based on the 3D mono-plotting principle using
equidistant as well as perspective 3D geospatial images. Be-
sides, we expect that our ongoing image-based georeferencing
developments will significantly improve the demonstrated
absolute 3D point determination accuracy. Our developments
will also lead to improved orientation accuracies so that we
might eventually omit one 360° panorama camera. In this
case, we will be able to create stereo images with virtual ste-
reo baselines resulting from vehicle movement.
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