NAPLPS
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NAPLPS (North American Presentation Level Protocol Syntax) is a graphics language for use originally with videotex services. It is unclear if it was ever used in this role, although the basics of NAPLPS were later used as the basis for several other microcomputer based graphics systems.
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History
In the mid 1970s a number of firms were rolling out videotex services, although the most popular by far would be in England. Character codes are sent to users' televisions by encoding them as dot patterns in the invisible "vertical blanking" area just off the top and bottom of the visible portion of the TV signal. A circuit in the TV decoded these signals back into text pages, which the user could select among. The data rate was quite slow, about 600 bit/s, resulting in largely static pages.
At about this time the Canadian government decided to create its own "second generation" service that would support both text and graphics, called Telidon. To start they used up considerably more of the "wasted" portion of the TV signal, and increased the signalling rate to about 2400 bit/s. To this they added a "backchannel" that send data back to the hosting computers, typically over phone lines.
But the real effort centered on creating a simple graphics language that would allow a more complex circuit in the TV to decode not only characters, but simple graphics as well. To do this the graphic was encoded as a series of instructions (graphics primitives) like "polyline" which was represented as the characters PL followed by a string of digits for the X and Y values of the points on the line. This system was referred to as PDI (Picture Description Instructions).
Telidon was so impressive that AT&T decided it wanted in on the project. They added a number of useful extensions, notably the ability to define your own graphics commands (macro) and character sets (DRCS). It was sent to the ANSI board for standardization and became ANSI X3.110, NAPLPS. As with all too many standards written by governments or more than one company, the original simplicity of NAPLPS was drowned in a huge document describing many issues that could safely be ignored.
But it soon became clear that there was no way to make money on a read-only service (a fact many in the web discovered again 20 years later). Unlike the UK where teletext was supported by one of only two large companies whose whole revenue model was based on a read-only medium (television), in North America Telidon was being offered by companies who worked on a subscriber basis and couldn't figure out how to make money.
Various two-way systems systems using NAPLPS appeared in North America in the early 1980s. The biggest North American examples were Knight-Ridder Corporation's Viewtron, based in Miami, and the Los Angeles Times' Gateway service, based south of L.A in Orange County. Both used the Sceptre NAPLPS terminal from AT&T. The Sceptre contained a slow modem that connected over the consumer's telephone line to host computers. The Sceptre was expensive whether purchased or rented. Despite huge investments by their parent companies, neither Viewtron nor Gateway lasted into the second half of the decade.
Other early-1980s NAPLPS technology was deployed in Canada, both as a way for rural Canadians to get news and weather information and as the platform for touchscreen information kiosks in Toronto. That city was the North American nexus of NAPLPS and the home of Norpak, the most successful of NAPLPS-oriented developers. Norpak created and sold hardware and software for NAPLPS development and display. TV Ontario also developed NAPLPS content creation software.
In the late 1980s, Tribune Media Services and the Associated Press operated a cable television channel called AP News Plus that providing NAPLPS-based news screens to cable television subscribers in many U.S. cities. The news pages were created and edited by TMS staffers in Orlando, Florida, working on an Atex editing system. The news screens were sent by satellite to NAPLPS decoder devices located at the local cable television companies. Among the firms providing technology to TMS and the Associated Press for the AP News Plus channel was Minneapolis-based Electronic Publishers Inc. (1985-1988).
NAPLPS lived on into the early 1990s as the graphical basis for the Prodigy online service. And some bulletin boards were able to serve NAPLPS contents to callers on their 1200- and 2400 bps modems. But the technology's chief advantage in an era of slow telecommunication -- its ability to encode complex graphics in terse object commands -- became moot as data communication speeds increased and raster graphics compression became popular.
Legacy
Nevertheless NAPLPS's legacy lives on today. In the 1980s NAPLPS' basic geometry and command structure became the basis for the library-based GKS microcomputer standard, which was later implemented in Digital Research's GSX graphics system and later used in their GEM GUI. GKS was later extended into a 3D version, and additions to this resulted in PHIGS (Programmer's Hierarchical Interactive Graphics System), a former competitor to OpenGL.
Some videotex fans claim that NAPLPS was used as the basis for the SVG standard for vector graphics on the Web. However, the SVG standard does not refer to NAPLPS. The two standards are similar only in the sense that they both have basic commands for drawing rectangles, squares, polygons, and arcs — but those commands are common to virtually all vector graphics standards.
See also
RIPscrip a.k.a. Remote Imaging Protocol
External links
- Telidon Introduction (http://ewh.ieee.org/reg/7/millennium/telidon/telidon_about.html)
- Interactivity and the Popular Support for Telidon (http://www.wlu.ca/~wwwpress/jrls/cjc/BackIssues/16.2/devon.html)
- Telidon (interesting early history) (http://iml.jou.ufl.edu/carlson/professional/new_media/History/TELIDON.HTM)
- Telidon (http://friendsofcrc.ca/Telidon/Telidon.html)
- The Telidon History Project (http://www.telidonhistoryproject.ca/)ja:NAPLPS