Background pictures are special objects that can be created to act as passive backdrop on which the rest of the network may be overlaid.

Pictures are stored in an internal graphics format, as files on disk.  These "Picture" files must be present for the background to be drawn.  There is neither a limit to the number of background pictures that may be loaded into the network nor to the size of an individual picture.

In general, these objects can be manipulated in the same way as any other network object, with the exception that the <Ctrl> key must be used in conjunction with any other action.  Thus, pictures can be selected, deleted, moved, hidden, etc.  A picture may be re-scaled isotropically by holding down the <Shift> and <Ctrl> keys.

Three background picture formats are supported: .DWG, .DXF and HPGL/1. DWG and DXF files are supported in their native format.

See also Importing Background Pictures.

Hints on Background Picture Creation

The coordinates of a DXF or DWG file will be reset to those of the original file any time the edit background dialog is entered.

When using a HPGL/1 file the prime objective in creating a background picture is to maximise the detail while minimising the size of the HPGL plotter file and hence re-draw performance. Some practical tips:

  1. When generating a plot file from a CAD package, apply any plotting scale factors that minimize the plotted size of the drawing. Remember that HPGL plotters have a resolution of 0.025mm, so that very small plots can still provide reasonable resolution, however, the resolution is coarser with smaller size plots.
  2. Transform splines to lines if possible. Splines generate lots of plotted points. Transforming spline vertices to Line Polygon vertices dramatically decreases the number of generated vectors while retaining acceptable resolution. This transformation can usually be achieved by exporting the drawing in some text format, editing it, then importing again, eg. DXF format from AutoCAD®.
  3. Any number of individual files may be imported as background pictures and overlaid or tiled.
    1. The mapping between plotter pen numbers and picture colours can be altered from the default by editing the plotter default file (by default, PL_DEF) used by CVTHPGL. This will avoid making any modifications to the CAD package configuration. 

    2. Minimize the amount of unnecessary text or other drawn objects in the background file. Since text takes more time to draw than most lines this will increase performance and drawing file size.