Papercraft: From 3D model to paper house (tutorial)

This tutorial deals with going from a simple 3D model to a full-color papercraft model, in this case a classical European-style house. At the end of the tutorial you can find the papercraft house to print out.

For this tutorial, I assume you are already somewhat familiar with basic 3D modeling. You don't need to know anything about texturing in 3D. Let's look at how to get your model to be a physical, colorful paper model.  

In my case, I used the freeware 3D modeling package Blender, which you can get here.
I also used the free software "Pepakura" to unwrap the 3D model to 2D, which you can get here.

Before exporting your 3D model, make sure the normals are facing outwards. To do this in Blender, just press TAB to enter Edit mode, press A to select everything, and CTRL+N to recalculate the Normals outside.

Export your model as an .OBJ file.

Export the model as an .OBJ file. OBJ is a universal file format for 3D models, so it is useful for transferring a model between different software packages.

Pepakura will allow you to "unwrap" the 3D model to something flat that you can print out. Start Pepakura and open the .OBJ file from Blender. Pepakura will ask you if you want to "Flip backfaces" and choose what is the "front". Just choose "no flip" and "finish". Flipping will essentially flip the "normals" of the polygons, but we already took care of that before exporting.

First result from "unfold" in Pepakura.

Press "unfold", "ok". Whoa, now we get kind of an unfolded mess. Seems we still have a bit of work to clean this up!

The most important tool is the menu you get when you right-click. There are some basic functions here that I will explain, which will allow you to greatly improve the result.

Select and move: Allow you to move the individual pieces to a better position on the paper.

Rotate: Guess what? It allows you to rotate the pieces. Don't worry about rotating pieces until later, when you've made all the decisions about joining/disjoining.

Join/Disjoin face: This is important. By double-clicking on a seam, this lets you seperate pieces of the model, automatically creating the "glue flaps" in between. It's important to choose which parts are connected, and which are to be glued together later. An easy workflow is to disjoin more than necessary at first, and then choosing which parts you want to join again. If you accidentally disjoin something you didn't mean to, just press CTRL+Z (undo). Or double-click on that line again, and the parts will snap back together.

We want to separate or "Disjoin" these faces.

Now they are "Disjoined"

Edit flaps: This will allow you by clicking on the "glue flaps" at the edges, to choose which part the flaps are situated on. By default they're kind of all over the place, but it's more esthetically pleasing when they are all grouped together, and much easier to actually cut on the paper later when they are grouped logically. You can either click on the flap seam or on the edge where you want them to go. By holding the mouse cursor over the flap, Pepakura will show you where it is supposed to go to on the other part with a red line. 

Chaotic flaps. The red line indicates the relationship.

After grouping the flaps, you will end up with something that looks less like spiky shoulderpads from Mad Max and more like this:

Ahh... order. Nice.

After editing the flaps you can play with rotating and placement of the faces. Once you've got a layout you are comfortable with, you can print it out. The free version of Pepakura will not allow you to save a file, however you can still print it. That means you can also print to a PDF. Of course if you are working on a large model, it makes sense to be able to save your progress, so you might want to consider paying for Pepakura if you are serious about papercraft stuff.

Now open the PDF that was generated by Pepakura with Photoshop (or the image editing program of your choice). Make sure the importing resolution is set high enough - by default Photoshop will set it to 72, but set it to 300 instead.

Layers in Photoshop.

Now to add the color, duplicate the layer with the black and white papercraft house on it, and set it to "multiply". Delete the original layer. Create a new layer, and place it underneath the Multiply layer. This way you can paint underneath, and the black lines will be on top. Alternatively, you could use photographic textures as well.

Layers in Photoshop, with the lines on top as "Multiply".

In my case, I painted this in Photoshop and did a lot of copy/pasting to save time. I cleaned up the edges after I finished the painting part, by marquee selecting and deleting the excess color.

Here's the final model, if you want to print it out and have a go at putting it together:

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