Retopology Workflow

Photogrammetry

Meshroom and 3DF Zephyr (free) were the two pieces of photogrammetry software tested.

Meshroom	3DF Zephyr (free)
No photo limit	50 photo limit
Anecdotally slower	Anecdotally faster
Node based, editable	Rigid, easier to use
Can orbit	Can scale, rotate, trim mesh
Struggled to get a single texture output	Multiple output options

I had issues with the texture outputs from both pieces of software. I was unable to get Meshroom to output a single texture over a UDIM. This causes issues down the workflow with Meshroom which would map the multiple texture maps onto the model incorrectly.

This is probably fixable with the Meshroom node architecture, but that is above my level of understanding.

3DF Zephyr consistently outputted a single texture, but I think this was also causing issues when finally importing into Unreal Engine - I'm unable to confirm that this was the case as I wasn't able to cross check with a third piece of software, and bypassed the issue by retexturing all the models in Mixer.

Overall I found Zephyr to be a superior choice. The ability to rotate and trim photo scans before taking them further down the workflow was nice with orientation. The 50 photo limit was a non issue, with even the larger scans I made topping out at about 35 photos. Plus the ease of use of the interface was a big bonus.

Meshroom | Check box seems to do nothing

Zephyr | Multiple output options

---

Retopolgising and Asset Clean-up

This is probably the weakest part of the workflow due to using all of this software for the first time.

I still find Maya tricky to use, and it's role in the process is one of the most crucial, especially with the UV mapping, this is something I need to spend more time working on.

After importing the scanned models from Zephyr/Meshroom into Maya, the goal is to create a low-poly mesh using the quad draw tool. This had a pretty sharp learning curve, quickly realising that it's much quicker and easier to start big, making large polygons of whole faces before refining by adding more edges and relaxing the mesh to the surface.

I had a lot of issues with some of the smaller scans with overlapping rocks, which led to holes through the surface. Adding more polygons would make the mesh jump through the gaps, so I had to try to omit the hole, or try to close it manually. This was tedious and probably a bad way to attempt the problem.

Gap caused from overlapping rocks

UV Mapping

My struggles with still being pretty new to Maya also caused some annoyances with the UV mapping process. I have a firm grasp of the principles - keep squashing/stretching of the maps to a minimum and if possible, hide your cuts in good positions. I was slow and found it hard to get the results I was aiming for - opting to move onto sorting out the rest of the workflow before revisiting.

I was initially less "bothered" to get the UV mapping done well when experimenting with overall workflow as being able to fix any issues by sculpting and painting in Mudbox seemed like an easy solution.

This potentially might've been OK in the short term if the texture mapping from Meshroom/Zephyr worked well and only needed some retouching. But ultimately all the textures needed recreating, which is fast in Mixer while also creating the other maps at the same time, but does showcase how shortcuts with the UV mapping can come back and hurt you.

Poor UV Cuts Showcased in Mixer

These UV cuts were automatically produced by Maya, and although had minimal stretching/squashing, it has lots of seams with prominent placement.

The screenshot shows how bad cut positions make using noise masks/layers difficult in Mixer. Adding many layers, adjusting settings, and using manual paint layers can hide the problem, but it's not ideal. Artefacts can also form on the seams where Mixer uses a displacement map.

---

Using Mudbox

The basic workflow I was using in Mudbox was to use the 'Transfer Details' tool to create several LODs between the source scan and the manual low poly created in Maya.

I would then use sculpting layers on the desired LODs to fix any issues - the most common issues being a point sunk deep into the mesh, or some polygons wrapping over each other.

Ideally I would have then transferred the photogrammetry textures on the lower LOD meshes, and used the painting tools to fix any areas where the captured texture is low resolution. Again, this wasn't really possible due to issues after testing importing into Unreal.

The issues with the texturing are prominent here in lower light levels

Tests with the same .fbx meshes, but new textures in Mixer revealed no issues, and was what I decided to progress with.

I ended up exporting a few of the different LODs from Mudbox as separate .fbx files for texturing. I was unable to find a way to export all the LODs in one file, if it is even possible. Ideally I would like to be able to do this, and use a singular texture on them all, since LODs are supported in Unreal.