Full text: Proceedings International Workshop on Mobile Mapping Technology

Table 1 
CCD image sensor : 
Control System: 
Image Device 
1/2 interline transfer CCD 
Maximum responsive frequency 
750 KHZ 
Image Area 
2.94mm x 6.45 mm 
Step Equivalent 
0.2 y m 
Picture Elements 
795(E1) x 596(V)z 
600 TV Line horizontal 
Linear range 
+ 20mm 
Electronic Shutter 
1/125—1/10000 sec 
Grama Correction 
r=0.25 0.45 1 
0.5 u m 
Grain Control 
AGC on/off 
Vertical frequency 
50 HZ 
S/N Ratio 
Better than 48 dB 
Input order 
Select direction 
Run x motor 
Run y motor 
Give direction 
Input steps 
Output positions 
Fig.2 Control procession 
making one pixel assembly error. 
JUDGING 3.1 Rough Assembly and Judging 
Before the system complete the assembly process, we 
first perform assembly error correction. Two steps 
complete this calibration. The first step is rough 
assembly. That is to control the assembly error on x, y 
direction less than 1/2 pixel. Although the displacement 
sensor of x, y direction can have this resolution, the 
sensor can’t detect the assembly error resulted from 
guide track linear error and vertical error between x, y 
direction. The second step is accurate assembly process. 
That is to precise measuring the residual error after 
rough assembly. This is done through the moiré pattern 
generated from CCD moiré effect [Zhong 1997]. Since 
the residual error is detected, we can adjust the number 
of steps of step motor to correct the residual error and 
record the data of displacement sensor at each assembly 
position: So far, the process of assembly is finished. The 
reason we limit the rough assembly error smaller than 
1/2 pixel is to prevent the assembly process from 
The whole target is separated into four areas(Fig.3), 
named 1,2,3,4 related to the four imaging areas in the 
CCD assembly process. We set area 1 as reference and 
adjust the position of CCD according to the large 
receiver until the assembly error is small enough. We 
take area 1,2 as example to explain how to adjust the 
error. When the error is not corrected the result is shown 
as Fig.4. It indicates that CCD assembly has errors on x, 
y direction. At first we adjust the assembly error on y 
direction to make strips on the whole image align on y 
direction (Fig.5). At this time, CCD assembly error on y 
direction is small enough to meet the need of rough 
assembly. There still remains assembly error on x 
direction, we adjust the position of CCD until the image 
after assembly is as Fig.6. In the same way, we set area 
2,3 as reference respectively to perform the CCD 
assembly of area2-3 and area 3-4. 

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