A Mesh Model You Can Actually Edit

A few months ago, I stumbled upon a workflow that allowed me to actually edit a mesh derived from photos.  I was talking with someone about how Fusion 360 and ReCap Photo both have tools that allow you "clean up" mesh models, but not ever truly edit the mesh.  Then I remembered that Fusion 360 allowed me to convert mesh models to T-Splines.  However, it had to be a Quad-Mesh, at the time I didn't understand what that meant.  I also noticed that ReCap Photo would allow me to export an OBJ and an OBJ(Quad), again at the time I didn't quite understand what the difference was.  After a little bit experimenting, and research, I was able to connect a few dots that opened up a whole new workflow for me.

The key to the workflow is understand what ReCap Photo means by OBJ (Quad), and how that relates to the Mesh to T-Spline conversion in Fusion 360.  The big difference between an OBJ and an OBJ (Quad) is that an OBJ (Quad) has a rectangular mesh as opposed to the standard triangular mesh.  See the Images below, taken from Fusion 360.

OBJ Mesh

OBJ (Quad) Mesh

The difference becomes significant when using Fusion 360's Convert Utility to convert a Quad Mesh to a T-Spline.  T-Splines are shapes defined by a rectangular mesh.  So in this workflow, the Quad Mesh generated by ReCap Photo will have a direct correlation to the T-Spline mesh.  Once the conversion is done, Fusion 360 gives you a new T-Spline body, which can be edited with any of the Free Form editing tools in the Sculpt Workspace.

So how do you go about doing this?  In the rest of this blog entry, I walk through a sample workflow that starts with photos of my drone and ending in Fusion 360.

1.  Take your pictures

In ReCap Photo, you start with photos.  I always try to get 50 to 100 photos from 3 to 4 elevations around an object, and 10 to 15 in each cycle around the object.  Recently, I have had some trouble with ReCap Photo giving me very poor, unusable models.  Then I realized something, I was standing too close to the object.  I was trying to out-smart the software by keeping close to the object and not capturing too much of the environment, which would be deleted later.  From my experience, you need those environment elements to help the software piece the photographs together better.  So now I have started making a larger diameter cycle and a smaller diameter cycle around the object.  

Below are just a few of the photos I took of the drone.

2.  Use ReCap Photo to Create the 3D Model

Creating the model from the photos is pretty easy in ReCap Photo.  You just have to select if you are using photos from an object or if you are using aerial photographs, which can be part of surveying  workflows.  In my case, I am using the object preset.  There is no scaling done at this point, that is handled after the model is generated.

Here is a quick video that shows how to use ReCap Photo to create the initial 3D Model.

3.  Model Cleanup in ReCap Photo

Once the model is generated, you can download and open the model in ReCap Photo.  Most often, my first step is deleting all of the the unnecessary mesh faces.  This is done by selecting the faces and hitting Delete.  My second step is setting the scale of the model.  Since we used photos, ReCap Photo will not have any idea how big, or small, the object is.  Using a measurement that we have taken from the model, we can use the Scale tool to identify those points in the model and set that distance in the model.

There are additional  mesh cleanup tools in ReCap Photo.  You will also have some mesh cleanup tools in Fusion 360, as well.  However, you will find that most will be unusable because Fusion 360 is expecting a triangular mesh, and will not recognize faces or edges of the quad mesh. 

This video shows the common steps I take after generating the 3D model and some of the mesh cleanup tools in ReCap Photo.

4.  Exporting to Fusion 360

When you have completed the scaling and model clean up in ReCap Photo, you are ready to export to Fusion 360.  ReCap Photo offers Quick and Advanced export options.  If you use the Quick options, you can specify which Autodesk product you want to export to and ReCap Photo will choose which export option is best suited for that product.  In this case, simply choosing Fusion 360 will set the export to OBJ (Quad). 

This video shows the export capabilities of ReCap Photo.

5.  Importing to Fusion 360

Importing an OBJ (Quad) into Fusion 360 is a straight forward process.  You go to the Insert menu and select Insert Mesh.

This video shows how to import the mesh in Fusion 360.

6.  Converting the Mesh to a T-Spline

The final step is to convert the mesh to a T-Spline, so we can leverage Fusion 360's T-Spline editing capabilities.  Fusion 360 does have a utility to do this in the Sculpt workspace.  I typically start a new Freeform shape, then use the conversion tool.  You will find that you still have the mesh body in the browser.  Once the conversion is done, you have full capabilities to edit T-Spline, using the tools inside the Sculpt workspace.  

From my experience, you do get a T-Spline mesh that is too dense.  I just compensate for that by deleting some of the mesh edges/lines.  That seems to smooth out the shape and makes working with the T-Spline a little easier.

In the case of the drone model, it has two planes of symmetry.  It is unlikely that I will be able to create the symmetry on the whole model.  What seems to work in this case is deleting three-quarters of the model, then using Mirror - Duplicate twice to make it a complete model again.

This video shows how to convert the model to a T-Spline shape and use the tools in the Sculpt workspace to edit the model.

Once you break down the workflow to the individual steps, you will see that it really is pretty simple.  I really like that I can truly edit the mesh that I get from ReCap Photo, which is something beyond what the clean-up tools offer.  I hope that you can put this workflow to good use.