I’ve been spending quite a lot of time preparing architectural line drawings for pen plotting, and one thing has become increasingly clear: an SVG that looks correct on screen is not necessarily a good SVG to send to a pen plotter.
Visually, two files can look almost identical. Mechanically, however, they can behave very differently.
Some of the things I now pay much more attention to are:
- whether the drawing is made from actual strokes rather than filled shapes;
- whether apparently simple lines are really single paths or complex outlined geometry;
- how many separate paths the file contains;
- whether there are duplicated or overlapping lines;
- the order in which paths are drawn;
- how much unnecessary travelling the carriage has to do between strokes;
- whether different line weights can be separated cleanly for different pens.
The last point is especially important for the kind of drawings I’m working on.
I often want to use several technical pens in the same drawing — for example, fine, medium and heavier line weights — so I need the SVG to preserve enough structure to assign different parts of the drawing to different pens.
A file can therefore be perfectly valid SVG and still be rather inefficient for plotting.
For example, a drawing containing thousands of short paths may take much longer than expected, not because there is a huge amount of ink on the page, but because the machine spends so much time lifting the pen, moving, lowering it again and repositioning itself.
I’m also finding that path optimisation is a balance.
It is tempting to optimise everything as aggressively as possible, but I don’t want an optimisation algorithm to change the geometry of the drawing, merge lines that should remain separate, or alter the intended line hierarchy simply to save a few minutes.
So I’m beginning to think of a “plotter-ready SVG” as something slightly different from an ordinary vector file.
Ideally, I would want it to have:
- clean single-line geometry where possible;
- no unnecessary duplicate paths;
- predictable stroke widths or colours;
- sensible grouping or layer structure;
- efficient path ordering;
- minimal unnecessary pen-up travel;
- geometry that remains unchanged by optimisation.
I’m curious how other people prepare their SVG files before plotting.
Do you clean and optimise them manually in Illustrator, Inkscape, Affinity Designer or another vector editor?
Do you use scripts or dedicated plotter software to reorder paths automatically?
And where do you draw the line between making a plot faster and preserving the original geometry exactly?