Creating patterns from official instructions

[N. W. Perry]

According to Brickset's random set browser, my next project is 4012 Wave Cops. This will require 3 new stickers (patterns for which already exist in some form), including one formed to the boat hull, and a new printed slope that appears in several police/emergency sets of that period.

For whatever reason, the official downloadable instructions for some of these late '90s sets are crystal-clear vector PDFs (as opposed to the newer ones that have raster images of not-so-good resolution). This means that I can open the PDF page in Inkscape and grab the pattern vectors directly from there:
       

This will give a much better resolution than any of the part photos I've seen so far—and probably better than any real copy of the part!

I had not heard of this technique being used before; has anyone got an established workflow for this process? Seems like it should be a matter of just straightening the vectors, resizing them to the slope face, importing them into—svg2ldraw, perhaps?—and probably re-triangulating. But we shall see…

[Philippe Hurbain]

I think it's Damien Roux who used a similar technique. But svg2ldraw often provides ugly triangulation and needs a lot of post processing. The last time I had a vector image, I pixelated it in good resolution and used img4dat on that!!!

[N. W. Perry]

I think it's Damien Roux who used a similar technique. But svg2ldraw often provides ugly triangulation and needs a lot of post processing. The last time I had a vector image, I pixelated it in good resolution and used img4dat on that!!!

Yeah, that's been my approach so far. But img4dat requires its share of post-processing as well, especially for shapes that ought to be geometrically regular. For example, img4dat can put points in a line, but you can't force that line to be orthogonal. But hopefully someday the SVG import feature will become available. :-)

Biggest trouble I'm having now is how to straighten the paths in the first place. Inkscape can take a rectangular path and distort it into a non-rectangular perspective quads, but there doesn't seem to be any way to do the reverse.

[N. W. Perry]

Well, for some reason I couldn't open the file in svg2ldraw at all. (The error message given is "Unsupported path command 'e'. The path will be skipped.")

And in any case, the vectors from the PDF weren't flawless, especially after being unskewed. Some funny artifacts and wiggly lines, and a lot of approximate geometry, so it was worth refining them before importing into img4dat. But an excellent starting point, to be sure!

I got everything cleaned up and aligned, made regular geometric shapes where they ought to be, smoothed all the nodes and corrected the colors to LDraw spec. Should turn out just fine.

Before:
   

After:
   

[Philippe Hurbain]

Well, for some reason I couldn't open the file in svg2ldraw at all. (The error message given is "Unsupported path command 'e'. The path will be skipped.")

Yeah, even more than poor triangulation, partial support of svg is the problem of svg2ldraw (or svg2dat). Looks like full svg support is an unwieldy task

[N. W. Perry]

Yeah, even more than poor triangulation, partial support of svg is the problem of svg2ldraw (or svg2dat). Looks like full svg support is an unwieldy task

In this case I think it's a bug; there doesn't seem to be any such thing as an e command, and certainly not in my file. I also made sure to save it as "plain SVG", hoping that would leave out any Inkscape-specific code. But no luck.