Refurbishing an old plotter

The war between wetware and hardware.
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ceptimus
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Refurbishing an old plotter

Post by ceptimus » Fri Oct 05, 2018 3:43 pm

I bought this old plotter on Ebay for £0.99 It's about thirty years old, and would have cost about the same as a small car when new. Plotters have been obsolete now for twenty years at least, having been replaced by large-format ink jet printers - but I think plotters still have a certain charm.

Needed a bit of maintenance and a slight repair but it's going now. Takes sheets of paper up to 25 inches wide and (I think) unlimited length. Certainly it can handle A1 paper.

First YouTube video I talk about the new pinch roller I made for it and then do a 'confidence plot' (this is what it calls a self-test).



Second YouTube video I drove it from a PC. It has a serial RS232 interface running up to 19200 baud. I'm writing software that converts photos into line drawings and hence plots. The software works at present (as you can see) but still needs improvement.


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Pyrrho
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Re: Refurbishing an old plotter

Post by Pyrrho » Fri Oct 05, 2018 4:39 pm

Awesome.
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Re: Refurbishing an old plotter

Post by Witness » Fri Oct 05, 2018 10:30 pm

Cool! :figamagee:

What kind of algorithm do you use for the image —> outline conversion?

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Re: Refurbishing an old plotter

Post by ceptimus » Sat Oct 06, 2018 12:01 pm

I'm using the Canny edge detector algorithm, invented by John Canny in 1986, to find the edges and then a simple 'search for connected pixels' thing I wrote myself to turn the edges into paths. I'm not happy with the performance of the second part (it's plenty fast enough, but doesn't always find the longest connected paths nor find them in the optimal drawing order) so I'm looking at other algorithms, travelling salesman and such to see if I can improve it.

Also the plotter holds up to eight pens in its carousel, so I'd like my program to choose different pens for different lines so as to use different colours and/or line thicknesses when plotting.

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Re: Refurbishing an old plotter

Post by Witness » Sat Oct 06, 2018 10:03 pm

Interesting task. There are quite fascinating papers from Victor Ostromoukhov about non-photorealistic rendering. Perhaps you'll get some inspiration there. :)