Notes on Kuzmin's "Full Photogrammetry Guide for 3D Artists"

Full Photogrammetry Guide for 3D Artists
taken from:
https://80.lv/articles/full-photogrammetry-guide-for-3d-artists/

This guide is very helpful and thorough. Kuzmin uses Reality Capture, plus some external software like ZBrush.


There are lot of steps, I've somewhat paraphrased here:

• Planning
• Choosing a good subject.
• Acquiring
• Kuzmin lists out the 'rules' of photographing for photogrammetry. 
• Follow the contours of your object. Shoot in three complete ring (larger subjects recommend up-down first, smaller subjects recommend completing one ring at a time). Roughly 12 degrees rotation between photos, with 60-80% overlap. Do not change focal lenth, exposure, or other settings. 
• Pre-processing
• Crop photos, remove background, cull out bad photos, remove rotation tag. Break into chunks (ex, front and back, close up details) and merge later.
• Remove noise and sharpen image. adjust exposure
• Processing
• Kuzmin uses RC. Throw all resources at processing and wait. He shares some of his project settings. 
• Alignment
• First the program aligns cameras. It is actually looking for unique features in each image, then calculating the sparse point cloud. A well shot batch should align 99% of the photos.
• Optional, add manual control points. This tells RC where to look for unique features.
• Then we calculate the dense point cloud and depth maps. This takes the most time and processing power. Throw the whole GPU at it and leave it alone til its done.  
• Mesh
• RC takes the dense cloud and converts to polygons.
• Fix
• There are probably errors. Kuzmin recommends taking the model out of RC at this point to correct it. Ex, zbrush has many tools to repair a mesh, and can be used to patch areas with the brush tools. 
• Kuzmin recommends simplifying the mesh here. The raw mesh is practically unusable because it is so large. 

• Texture
• I haven't tried this before-- Kuzmin brings the mesh back into RC under the assumption that it will sit exactly where the dense point cloud is, and that the repairs/edits made are minor. He then bakes the point cloud color data onto the mesh. Assuming the repairs are not too intensive, there should not be issues. But if the mesh is too different, this won't work.
• I am not sure this is the smartest approach... I will be testing the simpler repair tools in the stitching software before exporting it out. Ex, filling holes may be enough.
• Decimate
• This could be done in Zbrush. Kuzmin uses Meshlab.
• UV
• I suppose it is a good idea to have custom UV's if you are concerned about seams, and if you are following a PBR workflow (which uses multiple maps).
• Baking
• Bake color and normal down to the UV maps. Adjust/repair if needed.
• Kuzmin uses xNormal, which I think is obsolete? I believe Substance painter can handle this entire step with more tools.
• Post-processing
• Render it! Publish model. make it pretty.