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THE RELATIONSHIP OF TELIDON AND STANDARDS

H. Newman

Communications Research Centre

ABSTRACT

MetafiLes are files used for storing or Les metafichiers sont des fichiers qui transporting graphical data in a device inde­ servent a emmagasiner ou a transporter de pendent form. By developing a standard for l'information graphique de fa~on independante graphics metafiles, picture transfer between du terminal utilise. L'elaboration de normes computer graphic devices and computer graphic pour les metafichiers graphiques facilite le installations is facilitated. transfert d'images entre les terminaux et les ordinateurs graphiques. Telidon, a Canadian alpha-geometric system, is concerned with the trans­ Telidon, un systeme Canadien de videotex mission of pictorial information. The Picture alphageometrique, a un role important a jouer Description Instructions (PDI) used in Telidon dans la transmission de l'information graph i­ are drawing primitives. PDI have impact on the que. Le systeme Telidon utilise les instruc­ graphics metafile standards. Computer graphics tions de description de l'image (101), des and alpha-geometric videotex are converging and elements geometriques promitifs du trace compatibility between the two can exist by permettant l'independance des terminaux. Les developing a metafile standard which satisfies IDI ont des repercussions sur l'elaboration de the requirements of both. PDI could serve as a normes en ce qui concerne les metafichiers basis for such a general graphics metafile graphiques. L'infographie et le videotex standard. alphageometrique ont des points de convergence et la compatibilite est possible si l'on etablit des normes pour les metafichiers satisfaisant aux exigences des deux systemes. Les instructions de description de l'image peuvent servir de fondement pour l'etablis­ sement de normes pour ces metafichiers traitant l'information graphique.

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1. Introduction communi~Ation5 linps ~ptween ~ videotex terminal ann a central sections ?'-4 of this paper data bank. Broadcast videotex, or describe the alphageometric , is a service basen on the videotex system, Telidon, which was use of one-way communication developed in the Image channels, such as over-the-air Communications Laboratory of television or cahle television 's Department of signals. The entire repertoire of Communications. They contain some data pages is continuously excerpts from (11, which g~v~s a. transmitted and the lIser's terminal complete and netailed speclflcatlon waits for and selects the requested of Telidonand its coding schemes. page. Except for the delAy nnd the The coding schemes used in the number of pages available, as far alphamosaic videotex system are . as the user is concernen, both also described. Since alphamosalc modes of videotex operate in videotex uses character cells of essentially the same way. fixed size to form pictures, this type of system does not have a~y ~istorically, the first attempt relationship to computer graphlcs. to merge the technologies of Discussion of the relationship of telecommunications and computers videotex to computer graphics is for information nissemination to really limited t~ the the puhlicwas mane by the British. alphageometric variety. They developed an alphamosaic system called viewnata r?l commonly Section 5 describes the current known today as . Shortly work in computer graphics with thereafter, other countries began respect to standards and the role experimenting with similar systems. played by Telidon. France intronuced a system based on a somewhat improved display ?. What is Videotex? presentation coding called I\ntiope. In Canada, a system called Telidon, Videotex is a service which which differs radically from the ~ combines the technologies of others in its display presentation computers and telecommunications format, was developed. The Telidon for the purpose of disseminating design is based on computer information into the home or graphics principles i.e. pictures office. ~ user of the service can are built from their geometric access pages of textual and elements. . graphical information supplied by information providers -­ The basic Telidon system corporations and individuals who consists of a keypad, n CRT display create and put the information in unit, a r'lecoder (includinC] rlisplay the videotex data bases. ~ generator), a telecommunications television receiver or a video link and a central computer business terminal, augmented by a containing a Telidon data hase. microcomputer controlled interface Once connected with the data base, device, assembles and displays the users can select information by information that was requested by keying the appropriate command into the user. The transmission medium their keypad. Starting from an used in the service can be the fndex page which lists maior common carrier telephone line, categories of selectable other. interactive networks or a· information items, users choose an broadcast system. item and follow successive index pages to the one of interest. For There are two kinds of videotex example, a user may initially services. Interactive videotex is select "sports" and follow a service based on the use of successive branches in the dedicated two-way tree-structured data base to obtain

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statistics on a specific football to decone this nescription ann to team. The necoder converts the CRT draw the best line possible between display unit - 'an ordinary or the two enn points. On a high slightly modified TV set - into a resolution display, finer . videotex display unit. It receives increments are used to draw the the pages from the Telidon data same line that wouln be displayed base and converts them into a form in a coarse manner on a low suitable for display on the screen. resolution display. The accuracy with which coordinate positions are 1. I'.lphamosaic Picture Coding specified to describe these geometric primitives is a The mosaic videotex terminals, controllen parameter in the as neveloped in both the United communications code. It is simply Kingdom and France, are fixed left to the terminal to truncate format character oriented systems the coordinate description to the which restrict the display of accuracy that it can handle. information to rigid format textual messages and low resolution graphic Each drawing PDI has the mosaic images. The nisplay screen ability to set the current drawin~ is nivided into a fixed number of position to anywhere in the nrawinq character positions, typically ?4 space. Each has a defined final rows of 40 character positions for drawing position. The current a total of 91)0. Each character drawing position at the completion position is divided into a ~x2 of a drawing primitive is the matrix forming six sub-areas. defined final drawing position. For Thus, the effective resolution over each drawing primitive the the entire screen is 72 by 80 coordinate at which nrawinq begins positions. Each sub-area can be is either explicitly nefined or is assigned a colour value. By taken as the final drawin~ position combining the differently patterned of the previous drawing primitive. character positions, pictures are The exception to this is POINT, for formed. The pattern effect is which a new coordinate must always achieven by filling each sub-area be specifien. of the character position with the same or different colour. The The Picture Description character positions are stored in Instructions (PI)Is) are il compact the alphamosaic data bases and set of commanns for nescribing transmitted over communications pictures. Each command consists of channels in the same mosaic format an opcode followen by a number of in which they are later displayed. bytes of data. These commands are:

4. I'.lphaqeometric Picture Coding POINT - set the drawing position and Pictorial information for an optionally draw a alphageometric videotex system, po inl. such as the Canadian Telidon videotex system, is defined through LTNE - draw a line based on a specially designed code called its end points. Picture Description Instructions (PDIs). There are 1 types of POIs: I'.RC - draw a circular arc drawing primitives, attributes and based on a three control. The drawing primitives point definition. have been defined in terms of basic geometric primitives -- POINT, RECTI\NGLE - draw a rectangular area LINE, RECTI\NGLE, POLYGON and I'.RC. of specified For example, a line is drawn by winth ann height. specifyinq its end points. It is POLYGON - draw a polygonal area the responsibility of the ter~inal

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based on a s~ries Imolementation of a metafile of vertex points. standard would enhance the ~egree of interworking of the many CON'T'ROL - provide control over the different graphi~s systems ann modes of the would allow the portability of drawing commands. graphics data among these systems.

The basic character set used Although several graphi~s for text is the ISO ~4~ seven bit metafile nefinitions exist today character set. 'T'his is CSA Set No. (several universities, laboratories 1 in Canada and ASCII in United and corporations have developed States. their own), the standardiz2Ition effort has only hegun recently. ~ttributes may be applied to Several national stan~ards hodies, the drawing primitives as well as in particuli'H DI"! rr,ermi'lny) and to text. 'T'hey are: colour, blink, ANSl (), r,ave heen transparent~ area style, houndary working in this direction. style and text format. ANSI is working on what they The coordinate system for the call a Virtual Device Interface description bf geometric drawing standard. The VDI is a standar~ primitives is based on a normalized functional and syntactical Cartesian number system ranging specification of the control and from 0 to lover the visible area data exchange between of the display screen. This is device-independent graphi~s independent of the physical software and one or more resolution of the apparatus which device-dependent gr~phi~s device may be a television set of on the drivers. In con;unction with the order of 25~ positions of Virtual Device Interface, 'NB! is resolution in the horizontal working on a Virtual Device direction, or a high resolution Metafile standard. The VD~ contains display apparatus of 1024 positions a devic~-independent description of or any other resolution. Since a picture at the level of the VOl. coordinate positions are specified as a fraction of the width of the DIN has developen a display screen, the least 2-dimensional software package significant bits may be dropped called Graphical Kernel System for when they are not needed. supporting portable Computer Ained Design applications. 'T'his is the s. 'T'ELIDON and Computer Graphics basis for a ISO ~-n computer graphics standard. A meti'lfile S.l Graphics Standards specification is include('l in it.

In the world of computer The connection between graphics standards, the POIs of the alphaqeometric videotex i'lnd Telidon system define what is known graphics metafiles was made for the as a graphics metafile. A graphics first time when this type of metafile is a mechanism for the videotex was assigned to the ISO transfer and storage of graphics computer graphics working group in data in a form that is both device November 197 9. fl1 was suhmitted to and application independent. The this working group shortly standard that is being developed thereafter. It gives a functional for graphics metafiles would and syntactic description of the require that pictures must be POIs and demonstrates that POIs are storable on different media, suitable to serve as a graphics transportable among different metafile for applications other graphics systems and nisplayahle on than Telioon. different graphic devices.

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5.7. Telidun and Graphics ~etafile be used to input information into Standards Telidon data bases, ann Telidon terminals could be usen as low-cost A graphics metafile can he used computer graphics terminals. rn to retain graphical data and it order to move towRrd compatibility, also can be transmitted over a Telidon concerns shoul~ be cummunications link (eg. telephone consiilered when developing a netwurk). In order for Telidon graphics metafile stannarn. terminals to communicate with other kinds of graphics terminals, a 1;. Conclusion mechanism for the transfer of graphics nata that is device Since alphamosaic videotex uses independent must be developed i.e. character cells of fixed format tu a graphics metafile standard. form pictures, 'this type of system Before the information is does not have any relationship to transferred across the network, it computer graphics. The r.anadian is translated into a specific data alphageometric videotex system, furmat as defined by the standard. Telidon, is base~ on computer When a gr'aphics system receives the graphics principles. The Picture infurmation from the network, it Description Instructions in Telidon then translates the graphics are geometric drawing primitives metafile into the form expected by used to define pictures. They are its dev.ice r'lriver. The application, device independent and therefore, either Telidon or some other, then, are suitable to serve as the basis receives the data as if they had for a graphics metafile standard. cume from some local device. Telidon currently addresses a Functionally, the information different aunience than computer that is transmitted over the graphics but the differences netwurk is the same if it were between the two fields are rapidly written on magnetic tape. However, diminishing. The convergence can be the coding schemes used for each h\~tened and assuren by developinq medium ~iffers. The ihformation on a graphics metafile standard in the tape may be segmented into which the requirements for both certain block and record sizes. The Telidon ann computer graphics are information that travels over'the satisfied. network is formatter'l into ISO 7-bit communications codes. The r'lirection REFERENCES which the ISO computer graphics ~.G. Bown, 6.D. O'Brien, W. working group is taking is that, in Sawchuk, ,LR. Storey, "Picture any graphics metafile standard, the Description Instructions for the functional specification must be Telidon Videotex System", Technical separated frum any coding Note ~qq, Communications Research specification. The standard, then, Centre, Canadian Dept. of enables the use of any transfer Communications, Nov. 19 7o. medium which is the most suitable fur the application, without 7.. S. Fedida, ": ,1\n comprumising device independence. Interactive Information Service for the General Public", Proceenings of Computer graphics terminals as the European Computer Conference on well as Telidon terminals may be Communications Networks (lq7S). plugged into the same network. ~ graphics metafile standard could, ::1. 1-1. lIJe·t'lman, "A Computer Graphics in fact, define a graphics virtual ~etafile", ISn/TCq7/SC~/WG?/Nq7. terminal which would eliminate some of the incompatibilities between Telidon and computer graphics. Computer graphics terminals could

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