Introduction: Remixing Physical Objects Using 123D Catch, Meshmixer and Other Tools

In this instructable, I'll show you to scan a physical object using 123D Catch, remix and modify it using Meshmixer, and then print it using a 3D printer. In this case, I'm going to scan a rock, and add a human face to it.

In a previous instructable, I described the process by which you can make a copy of a physical object, without modification. However, once an object is scanned, the sky's the limit in terms of what you can do to it! This instructable extends the previous one by showing how you can make quirky edits and remixes using Meshmixer, and then using other software to slice it for printing. The capture process is the same as in the previous instructable.

You'll need:

Step 1: Photograph Your Object

The first step is to take a number of photographs (between 20 and 40) of your object, so that 123D Catch can assemble a 3D model. I'm using a rock that I found near my studio.

Here are some important tips:
  • Photographs should capture all sides of the target object, both all the way around, and top and bottom. A good approch is to take 20 objects all the way around, and then move up (pointing the camera down at the object) and take another 20
  • The object should not be moved at all during capture, and lighting should remain consistent. In effect, once the object is in place, you should move around it
  • The target object should take up most of the frame: either get close to the object or zoom in
  • While it is not absolutely necessary to maintain the same distance from the object all the way around, it does help the algorithm if distances are consistent
  • Consistent diffuse lighting all around the object works best.
  • Accurate focus is important - you will want to remove any out of focus shots
There are extensive tutorials available here:

So go ahead, take your pictures. If you're using the camera rig I referenced earlier, adjust the horizontal distance on the rig, and the camera zoom, so that the object fills the frame. Since the distance to the object will be consistent, you might want to focus manually.

When you're done taking pictures, save them all to a folder with a descriptive name.

Step 2: Build the Photo Scene

Now we'll submit the photos to the 123D Catch web service, to create a photo scene.

Open the 123D Catch application, and click the button for "Create a New Photo Scene". You'll get a dialog prompting you to select image files. Navigate to the folder where you put your photos, and select them all. (You can use the Ctrl-A shortcut to select all, or click the first file, and then Shift-click the last file to get them all).

You'll be asked whether you want to wait, or be sent an email when the process is done. You'll need to enter your email address, and a descriptive name for the scene. I prefer to wait for the upload part of the process, in case there are problems.

Once the files are uploaded, you can press the button for Create Photo Scene. At this point, I click the link underneath the button and ask to be emailed once the process is done. The dialog will retain the email address and scene title you entered earlier.

The scene calculation can take some time, about 15 to 20 minutes. Now is a good time to get a coffee or a sandwich.

Unfortunately, if the stitching process fails, you don't get notified. If after an hour or so you still haven't been notified, try the process again, except this time waiting for results. That way you will get a message if anything goes wrong.

If you DO get a notification, then the next step is to review and clean up the capture in 123D Catch.

Step 3: Clean Up Photo Scene

When the scene has been processed, the 123D Catch service will send you an email with a download link to your photo scene. Download it, and open it in 123D Catch.

If all goes well, you will see something much like the image attached. This is a near-perfect capture, and is typical of results you can get when the photos submitted are good.

123D Catch has captured the stage of the capture rig, as well as the target object. This can deleted by using the lasso selection tool to outline unneeded areas, and then pressing Del. Note that you can always orbit the target object by pressing Alt and dragging with the left mouse button.

You will still have a hole in the bottom of the object, which was obscured by the platform during capture. Save your scene, and export it as an .OBJ file for further processing in Meshmixer.

Step 4: Clean Up Holes With Meshmixer

Open Meshmixer, and open up the .OBJ file you saved in a previous step. Select the Inspector, and it will present a little spherical manipulator.

If you click on this, Meshmixer will attempt an automatic repair. What we want to do instead is RIGHT-click on the spherical handle, and this will select all the faces around the hole in the rock. Then select the option Erase and Fill from the Edits submenu. 

The fill will likely be quite bulbous, so use the scale parameter to reduce it to something more attractive. Approve the edit.

You can use the volumetric and smoothing brushes to texture the surface that has just been added, to make it look more natural.

Use the smoothing brush on the edges of the stone too, to make it consistently rounded on all sides and edges.

Step 5: Remix and Edit With Meshmixer

Adding a face is strikingly easy. For the purposes of this exercise, we will use the face that is already included in Meshmixer's bank of stock parts.

Select the face in the left-hand sidebar, and drag it onto a flat face of the rock.

It will appear with a manipulation widget: drag in the circular band to rotate the face, and drag the outward pointing arrow shape to scale it. Dragging the white sphere lets you move the face. 

Place the face in the right position, rotate and size it to fit, and approve the edit.

You can save your work as a Meshmixer project, and export it to an .OBJ file again. Be careful not to overwrite your original file!

Step 6: Slice for Printing With Netfabb Studio

Netfabb Studio has an extremely useful feature, the ability to slice a mesh into several sections, closing off the cuts to keep them manifold (a way of saying watertight, an object with a complete and unperforated shell).

We want to slice our object into two sections so that we can print it without using support materials. By cutting it in two, we ensure that we have a nice flat surface that contacts the build platform.

Open Netfabb studio, and then open the OBJ file you saved in the previous step. You can orient the object by dragging on the corners of the selection rectangle that appears when you click on it.

What you want to do is arrange the object so that a straight line cut will divide it in such a way that neither half has any unsupported overhangs. In this case, we want the cut to go across the widest part of the rock.

Use the rotation handles so that the widest part of the rock are on a horizontal plane. Then, drag the Z slider in the right hand sidebar. You will see cut plane represented on the rock as you move the slider. Press the Execute Cut button. It will show a preview of the cut plane. Make sure the checkbox for "Triangulate Cuts" is checked, as this will make sure that the cut faces are filled in. Go ahead and apply the cuts.

The object is now split into two parts, which can be selected individually. Export each part by going the Part menu, and then Export Part. Choose STL format. If you are prompted to repair the part at this point, go ahead and do so.

Step 7: Print!

Open the STL file you saved in the previous step in ReplicatorG.

Chances are, it will not be in the right position or scale. Use the Move button in the sidebar, and then the Center and Put on Platform buttons, to center the object.

Scale the object by typing numbers into the Scale dialog. Don't scale by dragging - ReplicatorG actually scales to higher precision than is shown in the dialog, so you can't know the exact value if you just drag. You need to enter an exact number, so that you can use the same value for the other part of the rock.

Save the STL from ReplicatorG, and generate G-Code for it. You will not need support material.

Open the other half of the rock. It will probably be UNDER the representation of the build platform, so you want to rotate it. Use the Rotate button in ReplicatorG and then click X+ twice. The part should now be on top of the build platform. Use the Move button the center it and put it on the platform. 

Press the Scale button, and then enter exactly the same value that you used to scale the other half. This will ensure that the two parts will fit exactly.

Go ahead and print each part using the procedure for your printer, or send the STL files to a 3D printing service, such as Ponoko or Shapeways.

Step 8: Assemble the Pieces

You should now have two parts of an object that fit together exactly.

Stick them together. Cyanoacrylate glue (Krazy glue) works well with most plastics, and cures very quickly. A few drops of acetone can also be very effective with ABS, though it takes longer to set.

You should now have a lovely rock with a face on it!

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