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1 Introduction
This book will show you how to generate stereoscopic 3D video, which can be displayed a television or VGA monitor, and viewed using liquid crystal shutter glasses. Applications for such a camera include robots, telepresence experiments, stationary observatories, radio-controlled vehicles and other vehicles where the operator would benefit from viewing the world three-dimensionally.
In August 2002 the book was revised recently to include stereo ranging, which deals with how the stereo camera hardware can be used in robotics as the video source for determining spatial relationships between objects.
The text is broken into several sections. Section 2, How the System Works describes, well, how it works. This section introduces the basic ideas behind synchronizing board cameras and generating the stereo view, and describes system component options. Section 2 also discusses stereo ranging, how the stereo camera module can be applied to robot vision, and some of the problems that are associated with stereo ranging.
Sections 3 and 4, Cameras and Synchronization Circuit Board, comprise the main part of the book because they deal with how to identify the cameras that can be used, how to modify them, and, at the circuit level, how to synchronize them. Cameras describes which board cameras can be used for stereoscopic viewing, how the cameras should be modified for use in the module, and the method of synchronizing the cameras. Several board cameras are identified which can be used; vendors' contact information is included. Synchronization Circuit Board describes the circuit functions needed for the module, including the video switch, reset timer, and shutter control. This section includes timing diagrams for the more interesting signals, schematic and bill of materials.
Sections 5 covers camera module construction and basic operation, including camera alignment and shutter control.
Section 6 deals with shutter glasses and the various adapters and equipment needed to get the video onto a display for viewing. These include the adapters needed to connect to the shutter glasses, the RF modulator and the VGA converter.
Section 7 provides links to the ExpressPCB design files needed to build the board. You will also find the original Visio schematic drawings, and there are also two sets of screen captures of the various PCB layers of the sync and the VGA adapter boards. Section 8 describes a video transmitter and receiver set used to test remote operation. This particular set was chosen because of its cost, its ability to carry stereo audio, its cost, the fact it is intended to carry NTSC video, and its cost. Several sources are included.
Section 9 winds up with last words about what else could have been covered if I had another year to spend on the project.
Section 10 lists the sources for the parts, components and equipment used in the project.
The camera module and VGA adapter printed circuit boards were created using ExpressPCB version 2.6.0 from Engineering Express. This is a free software package available at www.expresspcb.com. The package will allow you to create artwork for small double-sided prototype boards, order them over the Internet and receive 2 or more boards within a week. Their Mini-board service is very cost effective for prototypes, but does not support multiple layers (beyond two-sided), or silkscreen or solder mask layers.
ExpressPCB only supports Windows platforms. The artwork (pcb) files were included in the download with this book. Understandably Mac users cannot use them, but printouts of the top and bottom copper layers, silkscreen and soldermask for the two boards were scanned into jpeg files and included in the package. These pictures are not to scale, but will at least provide a representation of the component layout and signal routing. To request replacements for these files, or to order circuit boards, send an email to pete@petesprojects.com.
Many features and functions are not mentioned that, if implemented, would cause this project to go on forever. These include camera focus and camera separation; stereo audio; camera lenses; light filters for outdoor use; battery power for mobile use. More of this in section 9.
The scope of the book has narrowed greatly from the original idea of building a free-roaming, radio-controlled vehicle that did not have to stay within sight in order to control it. In fact, what started this was the idea of not only driving such a vehicle to places I could not see, but to places that I could not go.
Remember that this is all "stereo video on the cheap." While the stereoscopic effect is very good, it may not look anything like the computer-generated video that you may be accustomed to seeing. Some people will be disappointed with the result.
Many things can cause the results to be less than satisfactory. Of course, the cameras need to be from the same manufacturer. And cameras, even from the same manufacturer, and even the same model, are not created equal. Fabrication differences at both the chip and board level can cause discernible differences in output between any two cameras.
The hardware techniques used to synchronize the two cameras and convert NTSC video to VGA will degrade video quality. First, half the picture is thrown away to create a stereoscopic video stream, and second, the necessary conversion from analog to digital and then back to analog again will reduce resolution and introduce distortion. Liquid crystal shutter glasses may suffer from "ghosting," where the alternate eye will see a ghost of the wrong image. Shutter glasses will also limit the amount of light from the display.
While viewing 60-frame-per-second video with shutter glasses, you will experience flicker caused by each eye receiving only half the number of fields displayed on the screen. This flicker may cause headaches. And using shutter glasses (as well as any stereoscopic viewing device) for prolonged periods may cause disorientation.
Using a radio transmitter and receiver for remote viewing will introduce more opportunities for video quality to be degraded. The ISM (Industrial, Scientific and Medical) frequency band of 2.4GHz may be convenient, but it is also where you will find interference from many devices, including microwave ovens and wireless networked devices (such as Bluetooth).
SVGA displays and head-mounted displays had to be dropped from the project because it was discovered during development that the methods used to convert NTSC video to SVGA are incompatible with the field-sequential stereoscopic video stream that this hardware generates.
Special problems arise when using the video module for stereo ranging. The software that must extract spatial information from the video expects to see the same data on the exact same data on corresponding lines of alternate fields. This means the two cameras must be aligned perfectly, and the mounting base must be strong enough to maintain that alignment. The mounting technique discussed in this book is only adequate for stereoscopic viewing. The reliable and precise alignment needed for stereo ranging may need to be augmented in the software.
But enough of that. On with the project.
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