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Automotive Lane Tracker
Architecture,
Next Generation
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Next-Gen Lane Tracker will be Hybrid
The next generation Lane Tracker will be a duel mode hybrid, combining
two different architectures: one for daylight and one for night time.
The camera topology consists of a single color CCD area array, capable
of randomly addressable scan lines; a day/nite filter selector; a relay
lens system; and the taking lens (front glass). Attached in close proximity
and alignment will be the special spread-beam LASER illuminator (for night
time).
The daylight approach uses the first three active scan lines of a NTSC
tri-color
CCD area array. The image data from the array's R, G, B, outputs will
be processed for Color Space Translation such that only
HUE
is extracted and used for White/Yellow Lines detection.
This approach has among its properties, the exclusion of vehicle shadowing
from the White/Yellow Line boundary detection problem. That is to say,
the confusion between longitudinal /near parallel vehicle shadowing and
White/Yellow Line edge boundaries has long been a problem requiring lots
of DSP processor time.
A second property is that it utilizes ambient light, reducing the complexity
of the LASER only based approach.
The night time line detection system utilizes the LASER
only based approach found in the previous generation Lane Tracker.
In this approach, unlike the aforementioned first gen lane Tracker,
the linear CCD array is replaced with the color R,G, B, area array of the
daytime system.
An examination of the spectral plot of the color CCD array reveals a
high sensitivity to the LASER wavelength, 790nm, in the RGB filter's NIR
"pop-up" region. |
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Lane Tracker System
(Next
Gen)
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TL Taking Lens (front lens)
RL Relay Lens
IFB Image Fiber Bundle
ALM Alignment Mover
LOR LASER Optical Rod
CL Collimating Lens |
OF Optical Filter
(selectable)
CCD Sensor
TEC Thermal Electric Cooler
LD LASER Diode |
ADC Analog to Digital
Convertor |
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Lane Tracker Front End
Combination Camera
Click
image to see larger version
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Combination Camera with Dual Filter Selector
| Filter F1 is a 3 stage
Dielectric Optical Bandpass Filter Fc = 790 nm, HPWL = 10 nm; Filter F2
is an Infrared Cut Filter (Schott Colored Glass, IR Reject Filter). |
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The Ideal Sensor
The ideal color area array sensor would have randomly addressable scan
lines, such that the active image field could start at some arbitrary selected
active scan line and either complete the field, or truncate
the scan to from the very next line or any contiguous group of lines,
i.e., the field could be from 1 line to 242 lines in length (typically,
3 lines).
The practical reasoning behind this approach are several:
1) random intermittent full image views of the roadway scene could
be captured;
2) this would allow greater control on light integration time, i.e.,
several line times to multiple field intervals n x 16.667msec.
Texas Instruments TC-286 Brief
Specs
Hi-Res BCMD Image Sensor for NTSC Color Applications. |
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The less-than-ideal NTSC Sensor
Some standard NTSC RS-170A, CCD sensors can be used for this approach
by, asynchronously restarting the frame transfer clock . The deficiency
in this approach is the latency of the first 20 scan lines that make up
the vertical interval. This would mean a fixed delay of 1,270 usec ( n
x 63.5 usec) before active imaging takes place.
Conclusions
In the practical world, this may not present a problem, that is, distance
between measurements "D"--worst case--would be: assuming a total of [23
(20 + 3 scanlines) x 63.5 usec = 1,465 usec frame rate] @ 60 MPH = 88'/sec
= 1,056 "/sec = 26,822 mm/sec, then D = 1.547" /sample or 39.30 mm/sample. |
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| HUE Extraction
1) Data Translation RGB - HSI Convertor DT7910 & ROM DT7971.
2) A real time SUM of Vectors circuit--analog or digital-- can also
do the RGB - HSI conversion.
Because this a radiometric not a photometric problem, the R G B inputs
can have any weight, e.g.., equal weights R = 0.33, G = 0.33, B = 0.33. |
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