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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004
Stereo image photographing system is composed of host PC and
trigger generator, and is required to have the following
functions.
* Image display function: Necessary to confirm the image
quality (photographing range, focus adjustment)
* Function to control synchronization signal: Control of trigger
generator (control of start and stop of stereo image
photographing)
* GUI application is necessary to operate the above functions.
The problem in recording high resolution digital image 1s the
time to write the data on HDD, and therefore, it is desirable to
install PC exclusively used for image recording. The risk of
frame missing is reduced by making image recording PC
independent from image display PC. Furthermore, the time loss
of writing on HDD can be reduced by distributing the tasks to
plural PC's.
(2) Calibration inside the camera
The internal correction value will be measured for each stereo
camera. It is essential to maintain the required measuring
accuracy as the cameras used are not measuring camera and
wide angle lenses are used. The correction value is measured
for the following items.
*Focal length
*PPS (principal point of symmetry)
*PPA (principal point of auto collimation)
*Radial distortion
Photographic measurement software sold on the market will be
used for the measurement of correction value. The correction
value measured in this way will be inputted as the correction
term of camera data by the stereo measuring system described
later.
(3) Calibration outside the camera
External position correction value is measure for stereo camera
by the following procedures.
* Establishment of reference point site
The reference point site will be established. This reference point
site is established to work out position of stereo camera by
spatial backward intersection. About 8 points having depth
against the stereo model will be set up as the reference point
and measured by total station, etc.
* Measurement of position and inclination of vehicle
Position self measuring system and stereo camera are mounted
on the vehicle and reference points are photographed in stereo.
At the same position, the position rotation angle of measuring
vehicle is measured by the position self measuring system.
* Calculation of correction value
The external position of each camera is calculated by spatial
backward intersection from the stereo image photographed and
coordinates values of reference point group. Also, the external
position of vehicle origin point (IMU) from the calculation
value of position self measuring system, and the three
dimensional relation between two external positions calculated
will be taken as the correction value.
The correction value measured will be inputted as the
correction term for the post processing made by position self
measuring sensor.
Secular change is expected to this correction value due to
physical factors such as attachment and detachment of camera.
Therefore, it is desirable to establish the reference point site for
correction value measurement on permanent basis and operate
them under consistent environment.
71
(4) Position self measurement and processing system
As POS / LV 420 is used as position self measuring sensor, the
analysis and processing software of Applanix will be applied.
This software is composed mainly of following three functions.
* GPS analysis and processing function
Analyzes and processes the GPS data of IPPS sent from ground
GPS key station and GPS mobile station.
* Integration processing of GPS and INS
Supplements the analyzed and processed GPS data of 1 PPS
with IMU data of 200 PPS and generates three dimensional
locus data of 200 PPS.
* Referencing process of external position
Calculates the external position factors of each image including
external position correction value of camera (three dimensional
offset amount from IMU) into the three dimensional locus data
of 200 PPS.
(5) Stereo measuring system
The following functions will be equipped with stereo measuring
system based on the requirements for development.
* Function to generate patch of stereo pair
Function to connect GIS data and stereo image data with the
GPS time as the key. Also, the function to search for the
photographing pair of the same time and automatically generate
the stereo pair parameter.
* Measuring system platform and data format capable of
mapping and site survey as well as data exchange of bilateral
direction
Not only the input and edition of geometric figure but also input
of attributes will be made possible. It will also be made possible
to directly supplement the portion that could not measured by
aerial photographing survey. In addition, it will be made
possible to input the site investigation to both of aerial
photographing survey and this system.
* Function to retrieve the stereo model
It is required to retrieve the necessary stereo pair from several
thousands of image files. The function to retrieve GIS-like
stereo model with the location and time sequence as the key
* Function to automatically convert the reference coordinates
group of measurement
The function to automatically convert the difference of
reference coordinates group between the aerial photographing
survey and close photographing survey
* [nput and edition interface 2
The interface of input and edition tool used for aerial
photographing survey, site investigation and this system will be
standardized. As a result, the discrepancies among the various
processes and workers will be reduced and seamless working
process will be realized.
5. DISCUSSION RESULT OF MOBILE MAPPING
SYSTEM AND CONSIDERATION RELATED THERETO
5.1 System configuration employed
In this Section, the overall configuration of mobile mapping
system is shown in Figure 5-1 and the configuration of
measuring vehicle in Figure 5-2.
