Anyone familiar with Blender's export to paper model add-on?

[Jsk]

So I've been thinking about reviving a project I started years ago: a Chesapeake Bay Skipjack card model. I originally modeled it in Wings3d (which I still use frequently) and wrote a script to extract UV coordinates from the 3d model and convert them to *.svg files which could then be printed out and assembled into a card model. Not being very good at 3d math, however, posed some real challenges in the writing the script which I was never able to completely solve. At the time there weren't many options for converting a 3d model to a card model except for Pepakura--but since I don't operate any Windows computers that was not available to me.

 

I've noticed that Blender now has an add-on that that seems to duplicate what my script did. But perhaps better? I've tinkered with it a little bit but I'm wonder if there's enough potential to continue. Blender being rather infamous for dumping you into the deep end right off the bat.

 

So has anybody come to grips with the add-on? Is it reliable?

 

[Jsk]

Hmmm...

 

I've been tinkering with this. Most of the on-line examples of people using this Blender Plug-in are just simple models and the plug-in works just find. But how many card models of cubes do you need? Ships are a bit more complicated. So the workflow I've been following is to export my Wings3d model to *.obj format, import into Blender; Define where the seams will be on the various parts and then export the model via the paper-model plug-in to an *.svg document; Edit the document in Inkscape. There are challenges--even with the fairly simple hull form of the skipjack.

 

First, what I really like about the plug-in is that it extracts the actual shapes of the polygons (well, triangles--the model must be triangulated) of the model and basically unrolls the model into 'islands'. The script I wrote years ago worked by extracting UV coordinates from the model but that opened a whole new can of worms as UV coordinates do not necessarily represent the true shape of the polygon.

 

This leads to the first challenge. The 'unrolling' is not totally predictable. While you can mark where you want seams (e.g. edges of the 'islands'), the plug-in will not hesitate to add additional seams (or even add islands) if it determines that the island will not lay flat. I've found that I have to go back to the original model and tweak it in order to prevent unwanted seams. But by tweaking the model you also change the way the plug-in 'solves' where seams are needed. So it can be a very iterative process.

 

I've not been entirely successful in getting rid of unwanted seams and islands. For example, the skipjack has a port and starboard bulwark. In the model, the geometry of each is identical except that they face opposite directions. Yet the plug-in resolves them differently--even though one bulwark is a duplicate of the other. In fact, while it resolves one bulwark as a single island, it insists on taking one triangle from the other and making it a separate island so that that bulwark consists of two islands while the opposite one is only one. Frustrating! I've also had the situation where the plug-in does not recognize two separate islands if they share a single vertex. (Actually, I don't think they share the vertex. In the original model it's two vertices that are located at the same coordinates.) I've not found a solution for this--it could be a Wings export or Blender import issue that merges the two vertices.

 

The second challenge is that while the plug-in will generate glue tabs and labels for the islands they really aren't very usable. I'm not too concerned about the tabs because I'd rather create them when I undertake the graphics work in Inkscape. But it would be nice to be able to name the islands or better yet have the plug-in recognize the names of the parts in the model. When creating the *.svg file the plug-in places the islands rather randomly on the page. Without labels it can be difficult to determine which bulkhead is which. There are 15 of them in the skipjack model scattered across the *.svg file. This would be a significant issue with a more complex model.

 

Thirdly, it seems that all the parts that you want to unroll have to be joined into a single part for the plug-in to be able to solve them. At this point I haven't found a way to undo that joining in Blender. So if I need to tweak the model, in essence I need to go back into my modeling program to do it. So for every change prompted by the results of the plug-in I need to tweak the model, export the model, import the model, reapply the seams and export to *.svg to see the results. I'm sure this is partly due to my knowing just the bare basics of Blender. That's because I've always found Blender work-flows to be terribly labor intensive. Catch 22.

 

While this sounds like a lot of whining I'm still optimistic. I guess worst case/best case scenario is that I can maybe translate the plug-in's Python code for unrolling and implement them in my old Ruby script. Or, maybe I finally learn Python and Blender and fix the 'challenges' myself in the plug-in. Ultimately, though, I'd rather be making models! None of these issues are show-stoppers. Yet.

 

Here's a re-arranged sample of the Blender's *.svg output. This is a 1/72 scale rendition shown on a 8.5x11in page:

 

 

 

 

[Jsk]

Well, it took 7 hours to figure out how to do it but I was able to name the islands and identify the individual bulkheads in Blender. It's tedious, though, and duplicates work I already have to do when creating the model. I'd really like to have them auto-named from the 3d model part names. Oh, well. I kept simplifying and simplifying the model to try and get rid of the unrolling anomalies I was seeing. If that keeps up I may end up with a boat in the form of a cube. That would explain why all the tutorials for this Blender plug-in show you how to make a cube!

 

Nevertheless, I think I've got enough to try a little proof-of-concept build just to see if the shapes are accurate. Maybe next weekend.