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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BS. Istanbul 2004
This data must then be processed and merged so as to obtain the
exterior orientation parameters of the camera.
VISTA DALL'ALTO (SCALA 1:2)
Figure 4. Diagram of aluminium bar design
3.1 Data acquisition and elaboration
The data obtained from POLIFEMO is complex, made up of:
- Data relating to the Position (spatial and angular);
- Data relating to the Time;
- Images.
There are different ways to process and store this data depending
on the type.
The images are recorded on the camera's smart card, while the
moment of shooting is memorised, along with the data relating to
the spatial position on the GPS system's smart card.
The angular position data obtained from the DMC system, after
being matched to the time data obtained from the GPS, is
recorded on the hard disk of the computer, making it possible to
compare the two. The storing of the images, of the shots and the
spatial position data is automatic but a special program was
written in C'* in order to synchronize DMC data acquisition
with the times obtained from the GPS receiver.
An example of an output file can be seen in table 5. The compass
was programmed to acquire data at a frequency of 50Hz while
the temporal signal was emitted by the GPS receiver every 10Hz,
therefore for every *GPS time" there are five values from the
DMC.
Time Az Elev Bank
17 01 39.20 132.7 4.15 -1.03
17 01 39.20 133.2 4.03 -1.10
j7 01 3920 134.] 3.99. -0.99
17 01 39.20 134.6 4.02 -0.90
1701 3020 133.5 411 -096
17 01 39.30 133.8 4.07 -0.98
17 01 39.30 133.6 4.09 -0.96
17 01 39.30 133.2 4.15 -0.96
17.01 39.30 133.8 4.11 -0.93
17 01 39.30 134.1 3.98 -1.00
17 01 39.40 133.9 4.11 -0.91
Table 5. An example output from DMC acquisition data
software
The images do not need to be processed but the data stored in the
GPS memory as well as that on the hard disk of the PC do, in
order to obtain the exterior orientation parameters of the
POLIFEMO System.
The GPS gives *.dat file containing all the information relating
to the spatial position of the WGS84 system GPS antenna
mounted on to POLIFEMO as well as that relating to the
moment of shooting. This file is elaborated by the Geomatics
Office software developed by Trimble and then combined with
the data from a fixed station, used as previously described, as a
local reference point.
The final processing of the kinematically post processed data
results in a file containing positional data (X, Y, Z)
corresponding to the moment in which the camera took a shot in
the Datum WGS84 (see table 6).
4. COMPUTATION OF EXTERIOR ORIENTATION
PARAMETERS
The processing described in the preceding paragraph supplied
the spatial coordinates and the angular values corresponding to
the phase centre of the GPS aerial at the moment of the camera
shot. One further processing phase is now required in order to
obtain the exterior orientation parameters of the image, in other
words, the spatial coordinates of the projection centre in the
exterior reference system and the inner orientation parameters in
relation to the exterior. To this end, a proprietary software was
written in Matlab. The software input data is the following:
- the file generated by the software written in C^" for
managing data obtained from the DMC (output in Table 5);
- the *dat file generated and processed by the Geomatics
Office software (output in Table 6);
- the X, Y and Z coordinates in WGS84 of the selected point
of origin of the Local Geodetic System (position of the
master station);
- theacquisition frequency of the GPS and DMC data;
- the calibration file of the bar containing the geometric
information regarding the reciprocal position. of the
components of the measuring system.
Figure 8 shows the relationship between the system components
and the reference systems used. Note the assumption that the
Local Geodetic System (the exterior system) and the System
Body (linked to the compass) are parallel at rest (when a = 0, à =
0ew= 0).
Shooting Instant XwGs84 Z WGS8A
YWGS84
15: 13. 17.033066 4687573.368 1230034.929
4132778.563
15 13 17.044898
4132778.563
15 13 24.196690
4132778.563
15 13 24.206617
4132778.563
15 13 24.218686
4132778.563
4687573.368 1230034.929
4687573.368 1230034.929
4687573.368 1230034.929
4687573.368 1230034.929
Table 6. Output of the Geomatics Office software (only event
markers)
