Category: photogrammetry
Capturing textures albedo
Building a Portable PBR Texture Scanner by Stephane Lb
http://rtgfx.com/pbr-texture-scanner/
How To Split Specular And Diffuse In Real Images, by John Hable
http://filmicworlds.com/blog/how-to-split-specular-and-diffuse-in-real-images/
Capturing albedo using a Spectralon
https://www.activision.com/cdn/research/Real_World_Measurements_for_Call_of_Duty_Advanced_Warfare.pdf
Real_World_Measurements_for_Call_of_Duty_Advanced_Warfare.pdf
Spectralon is a teflon-based pressed powderthat comes closest to being a pure Lambertian diffuse material that reflects 100% of all light. If we take an HDR photograph of the Spectralon alongside the material to be measured, we can derive thediffuse albedo of that material.
The process to capture diffuse reflectance is very similar to the one outlined by Hable.
1. We put a linear polarizing filter in front of the camera lens and a second linear polarizing filterin front of a modeling light or a flash such that the two filters are oriented perpendicular to eachother, i.e. cross polarized.
2. We place Spectralon close to and parallel with the material we are capturing and take brack-eted shots of the setup7. Typically, we’ll take nine photographs, from -4EV to +4EV in 1EVincrements.
3. We convert the bracketed shots to a linear HDR image. We found that many HDR packagesdo not produce an HDR image in which the pixel values are linear. PTGui is an example of apackage which does generate a linear HDR image. At this point, because of the cross polarization,the image is one of surface diffuse response.
4. We open the file in Photoshop and normalize the image by color picking the Spectralon, filling anew layer with that color and setting that layer to “Divide”. This sets the Spectralon to 1 in theimage. All other color values are relative to this so we can consider them as diffuse albedo.
Photogrammetry from 360 cameras
Agisoft PhotoScan is one of the most common tools used, but you will need the professional version to work with panos.
These do not support 360 cameras:
– Autodesk Recap
– Reality Capture
– MeshLab
medium.com/@smitty/spherical-and-panoramic-photogrammetry-resources-2edbaeac13ac
www.nctechimaging.com//downloads-files/PhotoScan_Application_Note_v1.1.pdf
360rumors.com/2017/11/software-institut-pascal-converts-360-video-3d-model-vr.html
WalkAboutWorlds
https://sketchfab.com/models/9bc44ba457104b57943c29a79e4103bd
CloudCompare – point cloud editor for photogrammetry
CloudCompare is a 3D point cloud (and triangular mesh) processing software. It has been originally designed to perform comparison between two dense 3D points clouds (such as the ones acquired with a laser scanner) or between a point cloud and a triangular mesh. It relies on a specific octree structure dedicated to this task.
Afterwards, it has been extended to a more generic point cloud processing software, including many advanced algorithms (registration, resampling, color/normal/scalar fields handling, statistics computation, sensor management, interactive or automatic segmentation, display enhancement, etc.).
photogrammetry using Autodesk ReCap Pro
MeshLab – processing and editing of unstructured 3D triangular meshes – photogrammetry
http://meshlab.sourceforge.net/
https://en.wikipedia.org/wiki/MeshLab
The system is aimed to help the processing of the typical not-so-small unstructured models arising in 3D scanning, providing a set of tools for editing, cleaning, healing, inspecting, rendering and converting this kind of meshes.
MeshLab unstructured 3D triangular meshes editor
MeshLab is an open source, portable, and extensible system for the processing and editing of unstructured 3D triangular meshes. The system is aimed to help the processing of the typical not-so-small unstructured models arising in 3D scanning, providing a set of tools for editing, cleaning, healing, inspecting, rendering and converting this kind of meshes.
http://meshlab.sourceforge.net/
