been developed into a multi-stereo mobile mapping system for a
wide range of applications. The system consists of an Applanix
POS LV 210 navigation system which is used to directly
georeference the digital industrial cameras. Typically, the
system is configured with multiple stereo camera systems with
sensors of two (FullHD) and eleven megapixels respectively.
All systems use GigE cameras with CCD sensors, global
shutters, 12 bit radiometric resolution and a pixel size larger
than 7 um. The cameras are equipped with wide-angle lenses
providing a large field of view of around 80 degrees and still
preserving a high geometric accuracy. The sensors are mounted
on a rigid platform and can be setup in various configurations
with stereo bases of up to 1.5 m. Depending on the mapping
mission the sensors are operated at 5 to 30 frames per second,
leading to dense stereo image sequences and raw imagery in the
order of one to several TB per hour.
A
Figure 2. IVGI stereovision mobile mapping system,
configured with a forward and a backward looking stereo
system and a downward looking profile scanner
3.2 Stereovision processing and exploitation software
As part of the SmartMobileMapping project a comprehensive
processing and exploitation pipeline (see Fig. 3) was developed
covering the following aspects:
* System calibration including calibration procedures for
interior orientation, relative orientation, misalignment and
lever arm parameter estimation for multiple stereo systems.
* Direct or integrated georeferencing of the captured stereo
sequences, the latter integrating GNSS/INS- and vision-
based observations (Eugster et al., 2012).
* Stereo image pre-processing yielding radiometrically
corrected, distortion free and normalised high resolution
image sequences (Burkhard et al., 2012).
* Dense depth map extraction and 3d point cloud generation.
The current dense matching solution is based on a semi-
global block matching algorithm as it is implemented in the
OpenCV library.
* Automated feature extraction, e.g. automated mapping of
road signs, exploiting the depth information gained from
dense stereo matching (Cavegn & Nebiker, 2012).
* Cloud-based hosting and interactive exploitation either
using a stereo client for stereoscopic measurements by
78
geospatial professionals or a mono client supporting
accurate 3d measurements by means of 3d monoplotting.
Stereo
Client
Mobile Mapping System
|
multiple | 4
stereo systems
b; onboard controller
D and data storage
INS/GNSS-based
navigation system
Mono
Client
y
| system calibration
i
LI
Web-based exploitation
y |
stereo sequence and 7] = xd
depth map processing | ||
IR ! eie | 3d
direct and integrated es a:
|
georeferencing digitized street / rail corridors
Processing System Cloud-based Hosting
Figure 3. Stereovision processing pipeline and workflow for
the mobile ground-based multi-stereo imagery
The introduced stereovision based mobile mapping enables
absolute 3d point accuracy of 3-4 cm (1 sigma) under average
GNSS conditions (Burkhard et al., 2012). Relative measure-
ments within a single stereo frame or between points in
neighbouring frames of the image sequence are better than 1cm.
4. AIRBORNE IMAGERY - ACQUISITION AND
PROCESSING TECHNOLOGIES
4.1 Leica RCD30 multispectral camera
For the airborne image acquisition, a Leica RCD30 camera was
used. The RCD30 is a four-band (RGB and NIR) medium
format camera consisting of a single lens and two frame sensors
behind a dichroic beam splitter (Wagner, 2011) (see Figure 4).
Figure 4. Leica RCD30 with OC52 Operator Control
and CC32 Camera Controller with GNSS/IMU
The following features make the RCD30 particularly interesting
for this type of road corridor survey:
* A 60MP single camera head delivering high-resolution co-
registered, multispectral RGBN imagery.
* A mechanical Forward Motion Compensation (FMC) along
two axis allowing proper operation also for large drift
angles.
