In the previous chapters, we have described the procedures required for plotting, drawing or typing information on the SC4020 without concerning ourselves with the destination of this information. The SC4020 has both hard copy and microfilm cameras available and it is possible to direct the graphical output to one or other of these (or to both). As far as the user is concerned, it behaves rather like a normal pen-plotter having a roll of continuous paper divided up into plotting areas 7.5in square together with a roll of microfilm divided up into frames. In the following description 'frame' will be used to denote either the microfilm frame or the 7.5in square plotting area. Any call of a graphical output procedure in the GROATS package will cause the correct plotting to occur on the frames that are selected. Once the user's identification has been placed at the head of his graphical output both outputs are advanced to a new frame and the hard copy output is selected. If no control procedures are called by the user, all output will appear on the current frame of the hard copy. In order to get output on microfilm, call:
select camera (I);
If I = 1 then the microfilm output is selected and the hard copy becomes unselected. All output commands after this call of 'select camera' will then appear on the microfilm frame only. If I = 3 then both hard copy and microfilm will be selected. To return to plotting only on the hard copy, the procedure 'select camera' must be called with I = 2.
In order to produce output on a new frame, it is possible to advance the output to the next frame by calling
advance film;
This will advance the selected outputs to the next frame position ready for a new frame of output to be produced. The ability to advance the frames on microfilm and hard copy separately and to output graphical information on only one or other of the two output forms means that two distinct types of output can be produced on a single run. For example:
select camera (3); draw sine curve; select camera (2); advance film; draw cosine curve; advance film; select camera (3); draw tangent curve; advance film;
would cause the sine, cosine and tangent curves to be drawn on three separate frames of hard copy while the sine and tangent curves are output on the same frame of microfilm. This switching of output streams on and off can be quite useful in microfilm work. A selection of the frames produced on microfilm can be output on hard copy for debugging and monitoring purposes.
The fact that both output streams can be turned on and off independently does mean that the user could get confused as to the order in which frames had been produced. For example if alternate frames were being output on hard copy and microfilm then it might be difficult to merge the two. To help the user, a count is kept of the number of times 'advance film' has been called and this is printed at the top left hand corner of the selected frames after the 'advance film' procedure has moved to a new frame. The count is initialised so that:
FRAME 1
appears on the initial frame of hard copy that is selected. This frame count may be a nuisance in microfilm work and it can be removed by calling:
frame (I);
If I is negative then this stops the frame count being output. A positive value of I will reset the count to I so that the next call of 'advance film' will cause the new frame or frames to be numbered I.
The SC4020 hard copy output will be returned to the user in a roll. Unfortunately, this does mean that the output is difficult to cut and flatten if it is left rolled for any length of time. The Laboratory is looking into the possibility of getting a machine to cut the hard copy roll as soon as it is processed. To aid the cutting process, a cut mark is drawn for each frame outward from the bottom right hand corner. The user can stop this cut mark appearing by calling:
set cut mark (false);
The standard setting of the SC4020 plotting areas is called REDUCE IMAGE mode and produces hard copy frames 7.5in square and microfilm frames with the standard spacing between each. A second mode called EXPAND IMAGE mode is available and is intended for 35 mm microfilm users who require to abut several frames of microfilm to allow plots to extend continuously through several adjacent frames. The exact size of the frame in EXPAND IMAGE mode is adjusted for 35 mm film. The hard copy plotting area is also increased in size and in EXPAND IMAGE is approximately 8in square. The centre of the plotting area remains in the same position and expansion is uniform in both directions. The size of the hardware characters, however, does not change so that, in EXPAND IMAGE mode, the spacing between hardware characters increases and the characters become rather smaller than the equivalent software characters. To change to EXPAND IMAGE mode the user should call:
expand image;
A call of the procedure:
reduce image;
returns the user to REDUCE IMAGE mode. The procedures have no effect if the correct mode is already selected.
In Chapter 3, the procedure 'dark' was described which enabled vectors and software characters to be produced darker than the standard plotting intensity. The procedure 'dark' does not, however, alter the intensity of the hardware characters. It is possible to define two different intensities of these using the SC4020 hardware. Hardware characters are either produced in HEAVY or LIGHT mode. The standard setting used by the GROATS system is the HEAVY mode. If the user wants to change to the LIGHT mode he should call:
expose light;
The HEAVY mode can be reset by calling:
expose heavy;
As stated above, the hardware character modes, HEAVY and LIGHT, are produced by hardware and are therefore global and not defined just for the selected region. This is, of course, different from the 'dark' setting of vectors which is local to the region.
An interesting facility available on the SC4020 is the ability to produce a 'form slide' which can be used as a standard background to a set of plotting frames. The 'form slide' has to be specially produced and loaded into the SC4020. To superimpose the 'form slide' on the output frames currently selected the user calls:
project form;
Examples of possible 'form slides' are maps and business forms. A special Atlas Laboratory form slide is displayed on the identification frame and it is necessary to inform the operator that it is to be replaced by the user's own slide.
In the production of movies, it is often necessary to repeat the same or a set of frames many times. This could be achieved by repeated generation of the same frame many times. However the SC4020 does provide a more efficient method of doing this by hardware. There is a hardware facility for marking a position on the magnetic tape and later rewinding to this position and repeating the intervening plotting information several times. In the GROATS system, the information to be plotted several times must be preceded by the call:
advance repeat (0);
and is terminated by the call:
advance repeat (I);
The initial call advances the selected output to a new frame. All the frames between this frame and the current frame are repeated I times. The number of times the frames are repeated must be less than or equal to 31. There is no simple limit on the number of frames which may be repeated. It largely depends on the amount of information plotted on each frame. The total number of SC4020 records (ie magnetic tape blocks) repeats must be less than 511. If the user attempts to repeat more than 511 records then a diagnostic will be given.
