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title: Passive scanning
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# Passive scanning
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## Table of contents
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1. TOC
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# Multiview
# Photogrammetry
Photogrammetry is the collection and organization of reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant imagery and other phenomena.
<p>Photogrammetry was first documented by the Prussian architect <a href="https://opus4.kobv.de/opus4-btu/files/749/db186714.pdf">Albrecht Meydenbauer</a> in 1867. Since then it has been used for everything from simple measurement or color sampling to record complex 3d <a href="https://en.wikipedia.org/wiki/Motion_field">motion fields</a>.</p>
<p><img src="images/data_model_photogrammetry.png" alt="Data Model of Photogrammetry"></p>
<p>A typical medium resolution aerial photogrammetry scan of a barn. With 50-100 images a reasonably accurate model can be produced. Such models are often used in surveying and restoration projects from the scale of hand helf objects to cities.</p>
<p><img src="images/house_scanning.jpg" alt="House"></p>
# Stereo Matching and Photogrammetry
<p>Early uses in stereophotogrammetry, the estimation of 3d coordinates from measurements taken from two or more images through the identification of common points. This technology was used throughout the early 20th century for generating topographic maps.</p>
<p><img src="images/stereo_plotter.jpg" alt="StereoPlotter"></p>
<p>stereophotogrammetry is now being used for capturing dynamic characteristics of previously difficult to measure systems like running <a href="https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8348/1/Dynamic-characteristics-of-a-wind-turbine-blade-using-3D-digital/10.1117/12.915377.short?SSO=1">wind turbines</a>.</p>
<p>Photogrammetry is useful for outdoors settings, where all you need is a handheld camera and some patience. In this example, note the loss of quality towards the top, as pixel resolution becomes problematic:</p>
<div class="sketchfab-embed-wrapper"> <iframe title="Arc de Triomphe - photogrammetry" frameborder="0" allowfullscreen="" mozallowfullscreen="true" webkitallowfullscreen="true" allow="fullscreen; autoplay; vr" xr-spatial-tracking="" execution-while-out-of-viewport="" execution-while-not-rendered="" web-share="" src="https://sketchfab.com/models/65937fd27de647c0a8ac99ce8275c03e/embed"> </iframe> <p style="font-size: 13px; font-weight: normal; margin: 5px; color: #4A4A4A;"> <a href="https://sketchfab.com/3d-models/arc-de-triomphe-photogrammetry-65937fd27de647c0a8ac99ce8275c03e?utm_medium=embed&utm_campaign=share-popup&utm_content=65937fd27de647c0a8ac99ce8275c03e" target="_blank" style="font-weight: bold; color: #1CAAD9;"> Arc de Triomphe - photogrammetry </a> by <a href="https://sketchfab.com/nicolasdiolez?utm_medium=embed&utm_campaign=share-popup&utm_content=65937fd27de647c0a8ac99ce8275c03e" target="_blank" style="font-weight: bold; color: #1CAAD9;"> Nicolas Diolez </a> on <a href="https://sketchfab.com?utm_medium=embed&utm_campaign=share-popup&utm_content=65937fd27de647c0a8ac99ce8275c03e" target="_blank" style="font-weight: bold; color: #1CAAD9;">Sketchfab</a></p></div>
<p>Geometry and texture/color in one workflow.</p>
<p>Affordability and flexibility. Depending on the end use application almost any camera will work given there is enough light and your post processing software is robust.</p>
<p>Real time feedback and processing as models improve. <a href="https://mars.nasa.gov/technology/helicopter/#">Ingenuity Drone</a></p>
<p><img src="img/lidar_vs_photogrammetry_drone.jpg" alt="Drone imaging"></p>
Precision is improving but can still be completely thrown off by certain light conditions in much the same way LiDar struggles with smooth surfaces.
Increasingly industry pairs vision systems for photogrammetry with laser systems to balance the benefits of both.
<p><a href="https://www.autodesk.com/products/recap/overview?term=1-YEAR">Autodesk ReCap</a></p>
<p><a href="https://www.agisoft.com">Agisoft Metashape</a></p>
<p>iPhone and Android apps for photogrammetry and now LiDAR scanning have multiplied over the last 2 years. The primary driver is product placement, however some open source options are making way for both art and art preservation</p>
<a href="https://www.myminifactory.com/scantheworld/">Scan the World</a>
<p><a href="https://projectmosul.org/">Rekrei</a></p>
<p><a href="https://www.adobe.com/products/aero.html">Adobe Aero</a></p><p><a href="https://www.adobe.com/products/aero.html">Adobe Aero</a></p>
<p><a href="https://www.scandy.co/apps/scandy-pro">ScandyPro</a></p>
<p><a href="https://www.bellus3d.com/faceapp/">Bellus</a></p>
<p><img src="img/bellus.jpg" alt="Bellus"></p>
<p>Intrinsics and extrinsics parameters</p>
<p><a href="https://en.wikipedia.org/wiki/Levenberg%E2%80%93Marquardt_algorithm">Levenberg–Marquardt algorithm</a> or damped least-squares algorithm (dls) are used to minimize the error across 3d coordinates. This procedure is typically called <a href="https://en.wikipedia.org/wiki/Bundle_adjustment">bundle adjustment</a>.</p>
<p>Groundwork camera properties and standards for USGS photgrammetry surveys.</p>
<a href="https://www.sciencedirect.com/science/article/abs/pii/0031866373900069">Welch 1973</a>
# ML for Photogrammetry
<a href="https://www.pix4d.com/blog/machine-learning-meets-photogrammetry">Pix4D</a>
<p>Improving accuracy while scraping information on the contents of photogrammetry data sets.</p>
# Open Source Photogrammetry
# Light Field