After defining the view surface, it is necessary to define the portion of this surface which is to be used for plotting the graph. All lines and symbols (except for labels drawn by <#837#>plbox<#837#>, <#838#>plmtex<#838#> and <#839#>pllab<#839#>) are clipped at the viewport boundaries.
Viewports are created within the current subpage. If the division of the output device into equally sized subpages is inappropriate, it is best to specify only a single subpage which occupies the entire output device (by setting <#840#>nx=1<#840#> and <#841#>ny=1<#841#> in <#842#>plbeg<#842#> or <#843#>plstar<#843#>), and use one of the viewport specification subroutines below to place the plot in the desired position on the page.
There are two methods for specifying the viewport size, using the
subroutines <#1050#>plvpor<#1050#> (page #plvpor#1051>
where in the case of <#848#>plvpor<#848#>, the arguments are given in <#849#>normalized subpage coordinates<#849#> which are defined to run from 0.0 to 1.0 along each edge of the subpage. Thus for example,verbatim4#
uses the top left quarter of the current subpage.verbatim5#
In order to get a graph of known physical size, the routine <#852#>plsvpa<#852#> defines the viewport in terms of absolute coordinates (millimetres) measured from the bottom left-hand corner of the current subpage. This routine should only be used when the size of the view surface is known, and a definite scaling is required.
To help the user call <#853#>plsvpa<#853#> correctly, the routine <#1054#>plgspa<#1054#> (page #plgspa#1055>
A further routine <#1056#>plvsta<#1056#> (page #plvsta#1057>verbatim6#