Paper Size Topics
The term ‘paper size’ discussed here is meant as the physical dimensions of the area to which the plotter can draw. Besides the HP-GL or HP-GL/2 data selecting the proper paper size is very important for overall result of plot.
From plotter view the thing is simple - the plotter receives HP-GL or HP-GL/2 data and plots them on a physical paper. This paper can be already preloaded in plotter and plotter cannot change its size or there can be plotters which can select the paper size (generally roll-feed plotters) in some range. However in both cases the plotter paper size must be know and selected before any effective drawing on the paper will be made. The badly selected paper size can lead either to a paper waste or to a clipped image (where some parts of the image are ‘out of paper’, i.e. invisible). In case of using the HP-GL language the selecting of a proper paper size is always the user job (the user should know the overall size of the plot and load the paper of proper size to the plotter). The HP-GL/2 language is more effective and it enables to determine a proper paper size in the data stream via the PS (Paper Size) instruction. This enables to create the plot files which contain information about proper paper size in its header and effectively use them whit appropriate HP-GL/2 plotters.
From the SPLOT view the situation can be more complex - basically the SPLOT software serves as a plotter simulator (it behaves as described above), however many peoples look for an HP-GL or HP-GL/2 viewer, i.e. they want to view all the image properly without explicit knowledge of a paper size. This task is not so easy as it can seem because the paper size is often a very important part of the HP-GL and HP-GL/2 data decoding process. By other words there can be HP-GL or HP-GL/2 plots which appearance highly depends on a selected paper size. For this task SPLOT contains a ‘plotter type’ called ‘HP-GL and HP-GL/2 viewer’ which always attempts to search so called ‘extents’ for a just drawn plot file. When they are found, SPLOT can use these extents to determine a minimal paper size to which the overall plot will fit.
Some people want to view plots in their natural boundaries (they need an HP-GL or HP-GL/2 viewer) and some want to view plots as plotted by the plotter (they need an HP-GL or HP-GL/2 simulator). Therefore the SPLOT program offers also so called ‘HP-GL/2 viewer’ plotter type which offers these paper size types with which the plot can be viewed:
Standard paper size: The SPLOT program ignores extents and selects paper size as a real plotter does. This mean that it uses a commanded paper size (either by the PS attribute of the embed tag or by the PS instruction in a plot file header) or if such commanded paper size is not available it uses the default paper size as it is defined in the Default Paper Size dialog (this selection corresponds to a pre-loaded paper in the plotter).
Actual paper size computed from extents exactly: The SPLOT program uses extents (if found) to compute a minimal paper size to which the overall plot will fit. That paper size is then used for drawing. This paper size is always maintained as an actual paper size. Note that plotter coordinates of lower-left corner of the actual paper are either zero (0,0) or are negative to the coordinates of upper-right corner (so the plotter origin (0,0) is in center of the paper). The coordinates of the upper-right corner of the actual paper are always positive. The X-dimension of the actual paper is always greater or equal to its Y-dimension (in non-rotated state).
Actual paper size computed from extents with relative addition: Using of the exactly computed actual paper size always causes a situation when some parts of the drawing close to edges of paper. Therefore you can use this paper size type with relative addition to produce a desired margins. However if the actual computed paper size has plotter origin (0,0) in the lower-left corner (always when your plot does not contain negative plotter coordinates) then the left and bottom margins cannot be added. The addition is expressed as a percentage of the computed paper size. To define it, use the Paper Size Options dialog.
Virtual paper size computed from extents exactly: This paper size is equivalent to an exact trim of plot along the extents. This trim is maintained as a real paper size. The corners and dimensions of that paper size usually do not meet conditions of actual paper size so it is called as ‘virtual’.
Virtual paper size computed from extents with relative addition: Using of exactly computed virtual paper size always causes situation when some parts of the drawing close to edges of paper. Therefore you can use this paper size type with relative addition to produce a desired margins. The addition is expressed as a percentage of the computed paper size. To define it, use the Paper Size Options dialog.
Note that only using of the standard paper size type corresponds to a natural paper size selection of a physical plotter. The other paper size types are used by SPLOT to ensure to user to view all parts of the plot in a convenient manner. However note that they need the plot extents to be found before drawing (i.e. there are two passes) and that there can be plots for which the extents cannot be found (then only the standard paper size type can be used). Also there can be plots for which some extents can be found, however they do not apply to some parts of the plot. By other words there can be plots (usually badly designed) for which you cannot view some or all parts of the plot regardless of the selected paper size dimension or for which the overall dimension of the plot will be always significantly smaller than the paper size dimension regardless of the selected paper size dimension.
Also note that the virtual paper sizes serve only to easy view plots in their extents without void paper margins and that these paper sizes do not correspond to any actual paper size in an actual plotter.
To set a default paper size type (i.e. the paper size type used for the first drawing of a new plot) use the Paper Size Options dialog.