|
|
This web cam is operational during daylight hours (about 7 AM to 11 PM). Due to limited Internet bandwidth, the web cam does not provide real time video. The image size, JPEG compression level, and refresh rate were choosen to accomodate available bandwidth. You can view sample resolutions to compare the effects of different resolutions and JPEG compressions. |
INTERNET EXPLORER USERS: MS Internet Explorer browser users may require the (AxisCamControl.ocx) software component which allows the browser to display moving images pushed from the web cam. This component should be installed when you visit the web cam web page, but just in case, try the Manhattan web cam site. You will see a download component prompt. After adding this component, return to web cam web page, you should be able to see the image.
HARDWARE: The heart of the system is the AXIS 2100 network video camera made by AXIS. Unlike other web cams that use a video camera connected to a computer, this camera "is" the computer. The computer and Linux operating system are embedded in the camera which connects directly to a network. This means a computer is not necessary to display a web page, since the camera contains a built-in web server. However, in this application, that feature is not used. A separate web server accepts updated images that are ftp'd over the network from the camera and serves them to browser clients. Using the camera's built-in web server, the number of web clients that can connect is limited to 10 users. By using a separate computer, more simulatanous users can be supported. The physical layer of the network camera is a 10/100BaseT connection. The 100Mbps rate allows up to 10 frames per second. In the current configuration, the camera is connected to a 10BaseT network limiting the maximum refresh rate to approximately 3 fps. The camera can further be adjusted for slower refresh rates.
SOFTWARE: General configuration information for this web cam is available at the AXIS technical notes web site. Specific configuration for this web page can be found in the technical note for Live Video on a high hit rate Unix/Linux site. The AXIS site includes several configuration options in addition to the configuration used by this site. Due to network bandwidth limitations, frame rate and viewing time limitations have been implemented. The image size is also limited. For example, although the camera is capable of 640 x 480 resolution, the display above is a 320 x 240 pixel JPEG image with medium compression. This configuration yields an image of approximately 9 Kbytes. Lower compression yields better quality but larger images (~90 Kbytes). This web page consists of standard HTML, JavaScript, and a perl NPH mode (No Parsed Header) script that prevents the web server from buffering output. For real-time video applications, it is imperative that all buffering is turned off. The NPH mode attaches the script's output directly to the browswer's input.
